Lexus RX 400h: Driving Tips & Tricks

PF_Flyer

Have a great tip on getting the most mileage performance out of your 400h? This is the place to share them with your fellow owners!

rocky7

Does anyone know if it’s normal for the RX 400 to shutoff if you stopped for a length of time.

I pulled over on my street to talk to a neighbor about our new car. During what I guess was 15 minutes the engine came on two or three times. My guess was to briefly charge the batteries.

At end of what I guess was 15 minutes the vehicle entirely shutoff. I restarted it right away. Only the battery seemed to be on. About 5 minutes later the car shut down again.

I started the car and was able to drive it home.

sinepman

Totally normal. The vehicle still uses power when in park (electrical etc). A/C has a particular high drain. Once the battery gets to a certain state of charge, it will automatically signal the engine to kick in to began the charge process. This protects the battery to avoid LOW levels of charge which would effect its life cycle.

rocky7

The engine kick in as it did a few times during the 15 minutes makes total sense. My concern was the vehicle shut down entirely after 15 minutes. Including radio, dash instruments, etc. It acted like after 15 minutes I needed to reboot the entire car. When it shut down after 5 additional minutes, I need to restart the vehicle.

If the engine came on periodiaclly to recharge thesupplement the battery drain or recharge, that makes sense. Not to have the vehicle shut down entirely first after 15 minutes and then aftrer 5 sdditionl minutes.

hongcho

My concern was the vehicle shut down entirely after 15 minutes. Including radio, dash instruments, etc. It acted like after 15 minutes I needed to reboot the entire car. When it shut down after 5 additional minutes, I need to restart the vehicle.

This does not sound normal, does it? Have you talked to your dealer about it?

Interesting...

Hong.

wwest

You can avoid the extended warm-up by turning the climate control completely off. Even if there is no heat "demand" the engine water jacket is still used to heat, moderate, the A/C's cooling level.

I think I have seen a note pertaining to our Prius that says you can set the A/C to run in "demand" mode wherein it does not need the re-heat pass through.

headless

I got my RX400h last week...one of the first at the dealership and in the area. I was so happy to get it...but since then, I'm SO disappointed...

I don't know how upset I should be at this point. I filled up my tank at 301 miles and checked to see I am only getting 23.4 mpg. This is downright horrible for a hybrid.

I don't understand it. I am not running the car hard and am accelerating as I would under 'normal' driving conditions.

I spoke to my car dealer and they said to allow 1000-2000 miles for a breakin period. I don't recall reading this in any of the reviews, as it appeared that everyone else was getting 27-31 mpg right 'out of the box.' I don't know what to do at this point? Should I sit and wait another 1000 miles to see, or should I contact Lexus and 'demand' they take the car in and see what the heck the problem is. My miles are a mix of highway and light traffic...

I have a few topics of interest:

1. The electric motor rarely if ever runs on its own. Any acceleration and the motor kicks in....and I'm not gunning it...if I'm under 5 mph, maybe it's only the electric...but otherwise, unless coasting, it seems like the motor is running...
2. The battery meter is NEVER full...ever.
3. The V6 seems seriously inefficient...whenever I accelerate, it looks like I'm under 10 mpg...my 1997 Infiniti does better than this!

I had such high expectations for this vehicle and I am so disappointed. I simply don't know what to do and everytime I get in the car, I'm stressed out with the crappy mileage my hybrid is delivering. Had I known it'd be so low, I would have opted for another vehicle. I am not impressed with Lexus at this point...this is my first one...at this rate, my last...I would like to get the posted mileage so I can really feel like buying a hybrid was well worth it....

Any good advice out there for a disgruntled new Lexus owner?

Thanks,

Headless

cyclone4

If you are sincere in what you state (I have no reason not believe you at this point) and you are not some kind of a MB guy trying to discredit Lexus, then I would say that something is wrong with your RX400h. Bring it to the dealer asap and have them look at it closely. As far as the battery meter is concerned, I don't think that it's neccessarily suppose to show it as totally full.

headless

I am not trying to discredit Lexus...in fact, I had a $1000 deposit down for this car for about a year...been waiting what seems like forever for this SUV...

I was soooo excited to get mine but after driving it now 300 miles, I have yet to see any of the hybrid benefits...

The salesperson keeps telling me to wait for the breakin period of 1000-2000 miles, but I'm finding it harder and harder to believe I'm going to go from 23 to close to 30 mpg...just seems like a leap of faith...and every time I get in the car, I'm stressed to even look at the mpg...I'm simply NOT a satisfied customer up to this point in time!

She (the salesperson) said that they (Lexus) cannot do anything with the car until the engine is broken in...however, she also assured me that if the car does not get the mileage that was posted by Lexus, they'll 'dissect' the car, and re-assemble it until it does what it's supposed to do...she remarked Lexus stands behind their products 100%...

I know Lexus is number 1 and has been for years...but that's not helping me right now...I'm just really stressed out that MY particular RX400h is performing well-below standards...almost like the Murphy's Law thing...here I was telling everyone I was going to get good performance and good mileage in my hybrid and my friend's Honda Odyssey is killing my mileage...I'm embarrased to tell anyone I got the hybrid...that's how pathetic it is (at least in my mind...23 mpg...come on!)

I feel 'stuck' right now...frustrated and angry that my 50k+ hybrid SUV is barely performing better than a RX330. I feel, to this point, I have wasted a lot of money.

Anyone else there with the same problems? I read EVERY review on the car...not ONE ever stated a breakin for good mileage...in fact, every review remarked mileage around 30 mpg. I'm NOWHERE even remotely close to that...as I said on earlier post, I feel, at this point, I've wasted my money...and am pretty bitter about it, if you can't tell...

I just need some reassurance that my car is going to get the mileage Lexus stated...as of this point, Lexus has not done much to assure me other than to tell me to drive it a few thousand miles before worrying about it...is this consistant with hybrid thinking? It sure isn't making me feel better about my over $50k purchase...

Headless!

cyclone4

I can tell you are in total agony. Officially, I don't think there is a break-in period as such. My dealer told me not to use the cruise control for the first 100 miles and that's about it as a break-in period. However, there have been some posters here that do indeed claim that the gas mileage will get substantially better after the first couple thousand miles of driving. Are you paying close attention to the consumption meter/screen so that it forces you to be very light with the accelerator? I'm confident that your problems with gas mileage will be rectified by Lexus in due time. Good Luck!

falconone

I also think you should wait for a decent break in period before you jump to conclusions. I've read some professional tests of the vehicle and it appears some of the journalists are getting expected mileage. I don't doubt what you're saying, but I 'd conduct a test after the break in period. Take a nice 60 or 70 mile drive at 68 MPH with cruise control on. Note what your mileage is over that stretch of road. Also take note of the prevailing winds and so forth. I bet you're going to get at least 27 or so MPG which you should be pleased with. As far as the battery is concerned, I believe it is operating normally. If it is anything like the Prius battery, don't expect it to be fully green all the time. Most of the time under normal driving conditions, it will be on the high side of the blue bars. This is an intentional design to keep the battery at optimum performance.

dmcmahon

Remember you won't get great mileage in highway driving; there, the gas engine is still having to lug around a 4500 pound SUV. The 30mpg figure was for city driving.

Bottom line is that Lexus positioned their hybrid system as a performance enhancement. If you wanted maximum mileage, a Prius might have been a better choice. I know, I know; too small, not luxurious enough; exactly the reasons I signed up for the RX wait-list.

Just in case anyone from Lexus reads this board, I think they need to refine their green car strategy a bit. The RX is a good first step. How about a crossover (Mercedes E350-like) vehicle weighing only 3500 pounds, and possibly with a more efficient V6 gas engine? How about a plug-in option so that you can keep the battery charged from AC and eliminate that "warmup/recharge" period some people are reporting?

Seems like I might just be better off waiting to see how the RX and other hybrids evolve over the next few model years.

gagrice

How about a crossover (Mercedes E350-like) vehicle weighing only 3500 pounds, and possibly with a more efficient V6 gas engine?

How about the "R" class MB? With the planned diesel hybrid I may just jump onto the hybrid wagon. Especially if it gets 40 MPG highway. It looks like it will be aimed directly at the RX400h. If you are more of a highway driver than city driver it may just be the ticket.

headless

Cyclone,

Thanks for your reply...agony...definitely...

I think I am being light with the acceleration...it seems that if I accelerate from a light on level ground, the engine will always kick in after a second or two...no way around that unless I want the person behind me beeping at me!

I did drive it on the highway a lot today but at a speed faster than 70 mph...in my area, I'd get run over at 70...the mpg kept decreasing until I figured I put enough 'higher speed' on the engine and backed off to about 68 mph and put it in cruise...the mileage did creep up from 23.5 to about 24.00 (on the screen)...however, when I filled it I found that the mileage divided by the 12.85 gal. I put in averaged 23.4 mpg...to my unhappy suprise...

I realize also that the hybrid engine (motor) will break in more slowly as the electric will help out from time to time...it makes sense that at very low speeds, the electric will help out...I always figured it'd run on electric only unless you hit about 20 mph...this is not the case...

May I remark at this time that the rest of the vehicle is awesome...the ride comfort, navi, stereo quality (non ML), adaptive lighting, etc...all perform per Lexus high standards...

I'm just hoping that I don't have to drive like grandma to get good mileage...if others have heard of longer breakins to achieve 27 to 31 mpg, then I guess I just have to wait and see...

BTW, the phone bluetooth is awesome...finally got my treo 650 to send my entire phone book into the car...by one-touch dialing my favorites, I can make calls while in motion...otherwise, no go...

Headless

headless

Crystal,

Thank you for your reply....

I am certainly over 17.5 mpg....as you can tell though, I'm getting impatient...I figured the great mileage would be achieved immediately...I guess I am finding that I am wrong with that thought...

I will check out the other forums you mentioned...I am glad I'm not the only one with this concern...I realize adapting to a hybrid takes time, but I figured 'normal' driving would still allow good mileage...I guess I'm just going to have to calm down and give it more time....as you said, 300 miles is not a few thousand and things should 'loosen' up with time...

Headless

headless

Falconone,

Thanks for the battery tip...I had a lot of things going through my head...like my particular RX was a dud...if it's normal for the battery to stick on upper blues or an occasional green, then I'm in the 'okay' area.

I did drive at 68 mph today on cruise for about 10 miles...my mileage indicator did go from 23.5 up to I think it was 24.0...but, when I filled it up, and did the math manually, it did only show 23.4 overall...that's why I was disappointed...

I guess I'll have to wait until I hit about 2000 miles to really 'worry' about it...

Most of my driving is in 25-50 speeds....is this 'bad' for efficiency? I am able to coast at times...and coasting is where the hybrids do best, right?

Headless

brightness04

23-24mpg average is not that bad. My 3.3L Highlander only got 16mpg when brand new, now it's up to 19mpg or so after a year and 17k miles. The per centage increase is the same 50%, whether it's 16 --> 24 or 20 --> 30, although the latter sounds better. In reality, if you drive the same 15k miles a year, the former (16 -> 24) saves more money.

cyclone4

Headless,

Hang in there! From everything we hear from all these knowlegable posters, things will get better with your gas mileage. Now, why I have been averaging more than 31 mpg in the city and about 27 on the highway while you have been averaging about 6mpg less, I have no idea. By the way, I have been doing normal city driving (stop and go, etc., etc.). I have now done enough of this to be confident in the results I reported on a couple of posts above.

headless

I never realized it could take THAT long to break in an engine...I realize the electric motor helps, so the gas motor may take a little longer...luckily, the RX uses cheapy gas...I'd still like to get it up over 27 mpg average...that's what I thought it would do 'out of the box.'

My friend's Infiniti FX35 uses 93 octane and gets combined 18 mpg...so, I guess with, at this time, 23.5 mpg and 87 octane, I'm not doing so bad...plus, the RX isn't giving up much performance...the thing is pretty fast...(yeah, yeah, and I'm not gunning it to test it all the time!)

Headless

wwest

is a function, strictly, of battery pack internal resistance to high inrush charging currents and the upper operational voltage and current limits of the solid state motor "drive" and energy recovery components.

Since the source of the regenerated energy, the drive motors, are not the primary limiting factors I would doubt if it would take anything more than a single 50KW motor to recapture all of the energy that CAN be recaptured in the RX400h during the most optimal slowing or braking circumstance.

For instance, quick, short distance stops would result in very little charge for the batteries.

It's most likely that learning to lift your foot, completely, from the gas pedal when you first see, realize, you wish to slow or stop will result in the best operational fuel economy one can attain. The heavier you apply the brakes the least likely it is that the batteries can accept the fast charging rate that a quick stop requires.

So, quick off the throttle and light on the brakes wins the day, fuel economy wise.

karkus

A 400h owner above said he was accelerating slowly but still getting bad mpg .. that's a common mistake when driving full hybrids (Toyotas and Fords). The best acceleration for good mpg has been described as "brisk". Don't floor it, but do accelerate reasonably fast. Unlike in regular automatic cars where accelerating quickly is not that great for MPG, full hybrids actually work better that way. Here's why: The engine is most efficient at high RPMs (true in pretty much all cars). So In a full hybrid, it is better to run high RPMs to get up to speed quickly, and then drive/coast with engine off (and just using the battery) instead of accelerating slowly which will run the engine at low inefficient RPMs the whole time.
This has been verifed by various Prius owners (and the 400h hybrid system should behave in the same manner). Some people even go so far as to use pulse driving - hit the gas, let it coast, hit the gas, etc. - but that's taking it a little far -just use cruise control and let hills accomplish the same thing for you.
Regarding the best speed for MPG - in a Prius it's 30-40 MPH (one guy got almost a 1000 miles on a tank at 35 MPH). I don't know what it is in a 400h but I'm guessing it's similar.
Another tip: Brake gently (or let it coast) - that puts the most juice into the battery. Hitting the brakes hard activates the regular (friction) brakes.

cyclone4

This is certainly interesting information. To this point in the testing phase with the RX400h, I have been accelerating rather slowly in city driving and getting surprisingly good gas mileage. I will have to try your method to see if there is any improvement.

tsotsi

I am still waiting for my hybrid and am trying to learn as much as I can from this forum. It seems to me that the secret to the hybrid's better fuel economy around town is in the way the driver brakes. Unless the gear(?) selector is in B, I understand there is no regeneration while coasting so the battery gets recharged when the brake pedal is pressed. But if it is pressed too hard, the conventional brake pads kick in, cutting down the time for regeneration as well as wearing out the brakes. So for maximum fuel economy, the driver should press the brake pedal hard enough to get maximum regeneration, but not hard enough to engage the brake pads. That way, the battery will be charged and ready for the next acceleration. I assume the conventional brakes have to be used to come to a complete stop.

But since I don't have my car yet, this is all theoretical for me. Can you owners tell me if there is some way to know -- from the gauges or from feel -- when the conventional brakes kick in? Does the regeneration slow the car fast enough so that you are not holding up traffic? Are you folks who are getting good fuel economy watching your braking? Are you using "B" in town? This is all new to me and I have the feeling some of you have the answers.

karkus

This advice is based on Prius driving, but it should apply to the 400h since it has a similar (but more powerful) hybrid system.
Yes, it is best to brake lightly or not at all. If you let the car "coast", the car will slow down a little (to simulte the behavior of an automatic) and charge up the battery a little. (Real coasting actually requires you to hit the gas just a tiny bit, but it may be hard to achieve). Pressing the brake lightly will charge up the battery more quickly, but since you spend less time slowing down, the total amount of charge stored will be similar as if you let it coast. Pressing brakes hard will use friction brakes as well. You can't tell how much friction brakes are being used. Yes, the friction brakes are used to come to a complete stop.
Anytime your foot is off the gas pedal, the engine should be OFF (unless it's still warming up) although at high speed it may actually be spinning but without fuel. That's part of the reason why it is best to accelerate moderately fast (not slowly) - about as fast or a little faster than most cars around you.
The B gear should only be used on long, steep mountain descents, where you have to ride the brakes for a long time and the battery would fill up anyway (at which point it will no longer accept more braking energy). In all other situations, the B gear is bad for fuel economy.

Worst 5 things for fuel ecomomy:
1) Short Trips
2) Cold weather
3) Short trips in cold weather (The WORST!)
4) Going over 70 mph
5) Hard braking

Top 5 reasons things to do for good fuel ecomomy:
1) gentle braking
2) 30-50 MPH
3) warm weather (~70 F, no A/C)
4) moderate acceleration
5) long trips

drivetrain

After about 200 miles, we've likewise been getting 23-24 mpg -- not bad, but not yet great. I'm not worried about this because (a) it doesn't make sense to reach even tentative conclusions about long-term mpg experience until a car has been driven at least several thousand miles, (b) the car's comfort, luxury, and driving performance are all outstanding so far, and (c) Lexus has been marketing the 400h much more as a performance car than as a low mpg car. Most important of all, my wife absolutely loves the 400h. Better mileage after the car has been broken in will be a plus, of course, but the fact that she is so happy with the car makes it a worthwhile choice for us in any event. If you're truly unhappy, though, you can always sell the car, probably for a hefty premium over what you paid for it. Judging from eBay transactions, some buyers who don't want to wait a year to get their 400h seem willing to pay $5K or more above MSRP to get one right away.

headless

Drivetrain,

I don't agree with you on Lexus's presentation...

It was meant to be a luxury, performance, hybrid SUV....with hybrid meaning very good mileage, decreased emissions, etc...

If this car came out with a 23 mpg sticker, do you think there'd be a waiting line for it? Didn't think so...

No matter how you wish to spin it, this car was meant to get very good mileage WHILE delivering increased power, extra goodies, etc...they were supposed to go hand in hand...

It seems that while Lexus delivered on the goodies and performance (for the most part), it has missed (thus far) the boat on the excellent mileage...

Whether that changes much is yet to be seen, but I'll betcha many of those on ebay would not be buying if they knew the car was going to fall very short of mileage claims...that's a very big deal...

When you introduce a new technology, you want 'the best.' The RX400h is thus far turning out to be a nice luxury SUV, but at a high price...we all paid that high price not for the navigation, bluetooth, and other goodies we can get elsewhere, but for the hybrid technology that was supposed to deliver very, very good numbers...there's simply no way around that!

Headless

marmadmax

We now have 685 miles on our 400h that we took delivery on 4/20. I reset the mpg calculator today. It was previously reading around 25.5 and that was probably 80%+ hwy miles. Today's adventure was a 55-mile round trip and consisted of about 10 miles city and the balance highway. The initial 5 miles city registered 32+ mpg and the reading at the end of the outbound portion of the trip was 31. The reading at the conclusion of the entire day's 55-mile trip was an even 29. I was surprised to say the least!

While driving, I made effort to be sure the electric motors operated as much as possible. I accelerated to speed slowly but steadily and when I got to speed I backed off the accelerator and the electrics then came on and seemed to stay on as long as there was no incline in the road. This seemed to hold true even at highway speeds when using cruise (63 mph). The current mpg went way up in these situations. In city driving, I made an effort not to tailgate, which permitted coasting instead of braking and accelerating when the car in front slowed or turned. I will be the first to admit that I altered my normal driving pattern somewhat - i.e., not sure I would want to go cross-country at 63 mph.

I also realize that computed mpg may not be accurate. Tomorrow when I fill up, I will get a better idea of what the real mpg has been for the past 360 miles. But, I am pleased to at least for now to have achieved near predicted computed mpg numbers.

cyclone4

This is much more like it marmadmax. As I have posted on several occasions (see my response to your earlier post), this is the type of gas mileage I have been getting. The last 55 miles you have been driving with the exact same style that I have been following. I am of the opinion that the folks that are getting "poor" gas mileage have not been following this method even though in their mind they are being careful.

I am very happy to hear of your success. I think that will be hearing a lot more of the excellent gas mileage stories in the coming days/weeks.

headless

To drive that way almost sounds 'fragile.' I understand you and cyclone are being as careful as possible, but can you really enjoy the car if you have to drive it so gingerly? What's the point of having performance if you can't utilize it? Do you think Lexus built the car so we could slow-poke around at 63 mph on the highway??..or accelerate as if we had a 2 hp engine? I'm not trying to offend you, but anyone reading your post would think we were all 'handicapped' by our vehicles...

In my area, the limit is 65 on the highway, so you'd get killed at 63...

I don't know how you do not tailgate with stop and go traffic...I try to keep my distance, but the RX does coast a lot (I guess good for recharging battery)...so, I usually end up catching up to people...

As far as the 'fun' component of the drive...we all know the car has great performance...the thing is downright fast...however, if you utilize that performance, your mileage is going to really be bad...so, this begs the ole question: at what price mileage versus performance?

It stinks we have to drive so cautiously to get good mileage...takes all the fun out of driving...I have a BMW convertible, thank goodness...that's a fun ride! And, believe it or not, it gets the same mileage as my RX...The RX is not any fun to drive if you care about mileage...and this is downright shame...Lexus did not introduce the RX400h this way...they moreso promised performance with efficiency...well, they're wrong...choose one...you won't get both!

I don't think performance should be SOOOO sacrificed for mileage...esp. with a hybrid...maybe the electric should be more tuned to allow for more of that torque as RPM go up...meaning, no kicking in of gas motor for a little longer...will still give plenty of time for charging, esp. when coasting...

I think the darn thing loses the gas mileage with acceleration from stop when you're on any road over 10 mph!!!! If the electric could be tuned to give more low end torque, anyone could 'get up to speed' without killing the mileage...as it is right now, accelerating on any road over 10 mph will get you rear-ended if you gently accelerate to get up to speed...as I've posted earlier, I drive mainly on 35-45 mph roads...when you are at a light and need to accelerate, if you take your time, the people behind you are going to beat you...the RX shouldn't lose sooo much efficiency with this normal driving...I think this is what is killing my mileage at the current time?

Headless

cyclone4

Headless,

One of the MOST important points that marmadmax made is about tailgating. Avoid tailgating. If you do so, you can anticipate coasting and breaking a lot easier. As I stated before, you do not have to drive like an old grandmother, but you do need use a lot of common sense. It does not matter much at all to the gas mileage if you accelerate to the desired speed at a moderate/constant rate. What matters a lot is what you do after you attain the desired speed. Nobody is asking you to accelerate so slowly so as to annoy the drivers in back of you. I will have a lot more to say about my wife's 400h and the gas mileage when I get to drive it a lot more this weekend.

headless

Cyclone,

I understand...get up to speed as quickly as you want...then coast as much as possible...you think it's better to accerate sharply for 10 seconds then accelerate slowly for 15-20??? (to get up to speed?)

I won't deny that 'timing' exactly how far you can coast is a learned art...it's gonna take time to figure that out...it's a shame we have to do it that way...that is where the car excels with mileage numbers...

I'm going to space the vehicle more and 'touch pump' the accelerator...being used to my Infiniti and BMW, I usually coast with foot on the pedal a bit to maintain speed...on the hybrid, that simply kills your mileage...

Are we to assume that the hybrid was configured to coast more than the average vehicle...meaning, less engine braking???...hence the need for the 'B' gear...or 'engine braking' gear, should we need more engine braking power? It seems like this car can coast a lot if you're level...

I will continue to work on the coasting issue...hilly areas aren't too good for this car either...my area has lots of rolling hills in 35-45 mph limits, with lights...seems like when I have to stop and start again, esp. up hill, I get killed with the mileage...no way to coast when you have a .5 mile slow uphill climb...

I'll have to assume highway at 70 mph will get about 26 mpg...will have to try that in cruise to see...

I'm hoping engine breakin will also 'ease up' gas motor issues and get me over 25 mpg as opposed to the crappy 23 tops I'm getting now with normal mileage....

Also, it's super hard to get the car to accel. in just electric alone...basically impossible, if you're already moving along...the gas kicks in every time...even if you just touch the gas...

Headless

cyclone4

I doubt it was configured to coast more than the average vehicle, but who knows for sure at this point? The "B" gear should be used only for mountainous terrain. I think that the "B" gear will actually result in worse MPG.

As far as acceleration is concerned, it is better to just accelerate smoothly to the desired speed period.

hongcho

Just one comment...

In my area, the limit is 65 on the highway, so you'd get killed at 63...

I am in San Jose, CA and I understand what you are saying. However, if you stay off the fast lane (the right most lane), that's not going to happen. You feel you are going to get "killed", but that's because you are thinking like the person who's going to kill on the other car.

Anyway, with 400h, one probably needs to choose between "performance" and "fuel efficiency". As someone said, there is no free lunch.

As far as the performance of 400h, you can't really compare an SUV with a convertible coup, can you? If compared to 330, I am sure it can "perform" with the price of low to average fuel efficiency.

Just a thought.

Hong.

tsotsi

Still waiting for my hybrid, cyclone4, and I hope your research will help me understand how to drive my hybrid sensibly, when I get it. Straighten me out where I go wrong. My understanding is that in city driving many people suggest coasting. But when coasting isn't the battery charge/discharge a wash? Doesn't the battery only get recharged from slowing when the brakes are applied or the selector is in "B?" Let's say I want to gradually slow down (I am not a tailgater). Is it better to select "B" or gently apply the brakes or is it the same? When applying the brakes, is there a way of telling whether or not the conventional brakes are in use so as to avoid losing some of the regeneration? On the two-wheel drive model (which I have ordered) I wonder if the conventional brakes always operate on the rear wheels since only the front wheels are slowed by the generator.

Sorry to have so many questions, but I have the feeling that fuel economy depends on knowing how the system works. Since I don't have my car yet to experiment with I am going crazy trying to figure things out. You seem to be willing to try different techniques in order to optimize the use of the electric side of the hybrid. It is nice that a person can drive these hybrids just like any conventional car, but I am fascinated by the other possibilities.

cyclone4

Yes you do have a lot of questions. Unfortunately, I cannot answer most of them. Coasting definitely helps a lot on gas mileage. Don't select "B" unless you are in mountainous terrain. I don't think you need to worry about the battery being recharged because of coasting. The system takes care of itself. Don't ask me how. I don't know the intricacies of the system. And, frankly I don't care exactly how it works. All I know is that in my case anyway, with the 400h that my wife and I own, I am very pleased at the results I am getting by following some common sense rules of driving to attain the best gas mileage. Incidentally, my wife has not been getting the MPG that I have been able to get. This is primarily do to the fact that her office is only about a mile or so away from home. Therefore, she makes a lot of 2-5 minute drives. Therefore, she gets worse gas mileage due to these very short trips when the vehicle is in the warm-up mode.

As far as your question about braking is concerned, I have no clue. Perhaps someone like "wwest" can answer this question and a few others that you have to your satisfaction.

tsotsi

Here is a direct quote from Car & Driver.com's May 5 blurb on the Prius:

"That “B” position will flummox those too timid to crack the owner’s manual. It stands for braking and provides the lower-range gearing required by our government, but in this position the car starts regenerating energy the instant you lift off the accelerator. Conventional piston-engine braking even kicks in at higher speeds. Prius enthusiasts will revel in the B-mode’s efficiency when driving in stop-and-go traffic where hybrids return their best economy. In addition to saving fuel, B-mode often negates the need to use the brake pedal. The faithful will surely get 400,000 miles out of their brake linings by planning ahead, leaving room to slow down, and eking every last scintilla of momentum out of each milliliter of fuel."

Has anyone tried this with their RX400h?

cyclone4

Here is what it states on the RX400h Owner's Manual: "Do not continue driving with the transmission in "B" for a long time. This may cause decreased fuel economy". It also states throughout this chapter that is used for braking. This to me implies that it should be used in mountainous terrain only. Also, does it not make sense that if braking is applied even when coasting, the vehicle will lose MPG? I think that the battery is getting recharged regardless even when coasting. Perhaps somebody that really knows the ins & outs of this stuff can explain it better.

karkus

I don't think the C&D statement is entirely correct. First of all, the Prius (and 400h I presume) will always generate a small amount of electricity when you let off the gas pedal, regardless of whether you are in B or D. Applying the brakes lightly increases the amount of regenerative braking, and then at some point pressing harder will involve more and more friciton braking. B involves engine braking (compressing air in the cylinders) so you will lose that energy instead of putting it in the battery (plus maybe there's some extra regeneration). Using B will NOT improve your MPG under any circumstance, as far as I know, and should only be used on very steep long downhills where you would have to ride the brakes so hard that the friction brakes would be activated anyway.
Ideally you would let the car coast as much as possible, but that's not always practical, and the hybrids recapture some of your braking energy. However, generating electricity, storing it, and converting it back to mechanical torque all involve some energy losses, so really it's not anywhere close to 100% efficient.
Full hybrids (Toyota, Lexus, Ford) improve fuel ecomomy because
1) Engine is off when coasting, braking, or stopped
2) Some braking energy is recaptured
3) Battery power is used primarily when only a little power is needed - in those cases it's more efficient than running the gas engine at low RPMs
4) Gas Engine is used primarily when it can run at high (efficient) RPMs

Also, I saw people comparing when the gas engine comes on. It depends on various factors:
1) Temp: The engine will always run more if it's cold, especially during first 5-10 minutes
2) The battery level: Low = engine runs a lot, in part to charge up the battery. HIGH=engine stays off unless you need lots of power. (The computer tries to keep the battery in the upper-middle of it's range whenever possible)
3) How hard you hit gas pedal, and whether it's uphill or down.

skyfish400h

I do not see any inherent contradiction between the C&D comments and the Owners Manual. Both could be true in certain cercumstances.

Assuming:

1) That there is always regeneration going on whenever your foot is off the acc.
2) There is more than one level of electric braking so that it can increase when the brake pedal is applied
3) The CVT allows seamless blending of the ICE and EMF torques in both acc and dec modes.
4) The D vs B mode determines whether or not the ICE is added to the mix for braking. In D it is only the EMF and friction pads, in B its all three.

The first one (1) just makes sense to take advantage of the cars inertia whenever possible. (2) seems plausible given that it works that way in the acc direction. We know that (3) is true from the Lexus literature bragging about the simple beauty of the CVT design. The last one (4) could be easily determined with some experimentation.

My breif experment wth the B position was that it did offer some extra braking when you let off the acc... although it was no where near that of a lower gear such as 2nd on an auto or dropping down a gear on a manual.

Now the effects of this would be highly dependant on the compression generated by the ICE and since the car was brand new, I would think that effect would become more pronounced as the rings seated and compression improved. Also, I did not get to try out the B position at freeway speed, only on surface streets (although I did have it up to 60 mph at one point

At low speeds the B position would help your MPG by applying extra EMF braking, at higher speeds where the compression of the ICE is used for braking your MPG may suffer some because energy that could have gone to the batteries is wasted as heat in the ICE.

tsotsi

To me, coasting means that the car is not being slowed down or sped up by the engine or motors. While coasting the battery may be getting recharged by the ICE, but not by loss of forward speed . . . since there isn't any (or much). Either (or both) selection of "B" or pressing the brake pedal sends a signal to the computers that the driver wants the system to slow the car and use the system for regeneration. It seems that since at high speed the ICE also comes into play to slow the car in the "B" position, it is probably better to use it for economy at city speeds. At highway speeds, descending a mountain, it mainly saves the brakes. For maximum economy you want maximum regeneration when stopping so, since while coasting the car is being slowed by rolling and wind resistance instead of regeneration, it is actually better to use the brake pedal or "B" than to coast.

That is what I am getting when I put all of the comments together. Yes? No?

skyfish400h

Coasting in the 400h or any car for that matter involves some slowing due to the engine(s). In the case of the 400h the EMF engines help slow the car and use that to charge the batts, and (depending on the D/B thing) the ICE engine uses compression to slow the car.

The big difference with the 400h is that it should not be using any fuel for this, just the the compression of the air in the cylinders since the engine does not need to be "running" to be used as a brake.

To experience the difference between real coasting and simply letting off the acc peddel, try slippnig the gear selector into N... now that's coasting.

But don't try it on a down grade :surprise:

cyclone4

The Hybrid Overview Manual says that you will hardly ever see the battery status fully charged (green) unless you are driving down a mountain road. This makes sense since the battery is constantly being chaged while driving down a long mountain road. The typical status is "blue".

cyclone4

Short trips definitely give lousy gas mileage. I had the average up to 35+ when I was testing it around the city on a few occasions more than a week ago. However, my wife making a lot of tiny trips has since then, brought the average down to about 32mpg. This warm-up period really eats up the gas. I am convinced that as long as one does not have to make these very short trips this vehicle will do even better than the EPA estimate on city driving. But the reality of it is that some of us cannot avoid these short trips. Headless, I hope you read my response to you 4-5 days ago concerning my driving like an old lady and that's why I was getting this awesome gas mileage. Happy driving with the RX400h everyone!!!

wwest

hixon:

Your calculation method works just fine for averaging, but what if I manage to drive the vehicle for, say, 20 miles on batteries alone? For instance one of the posts was quoting fuel economy for a short 51 mile trip.

I'm really curious about all of this "special handling" driving techniques being espoused since our 2003 Prius doesn't seem to need any of that sort in order to render the stellar 42MPH overall that it has.

A "V8" powered RX that must be driven carefully, with "kidd" gloves, is that what the buying public really wants?

dylan hixon

Good luck getting 20 miles on batteries alone at any speed, let alone highway speeds, that post was a steady 55mph. The car wont go much above 15mph on electric only unless you have a very full battery, and accelerate very slowly (or go down hill). I fear that this is part of the performance otiented tuning philosophy Lexus has.

I will redo my calculation with the actual battery capacity if I can find it, but it sounds like I am a factor of two high. That would agree with my experience that the battery charge depletes pretty rapidly in electric only city driving. And in the future, I will correct for net change in battery charge when I test, altough the effect will be minimal.

Techniques like early gentle braking, avoiding jackrabbit starts, and use of cruise control are not special handling, they are basic common sense, and easy to do. The beauty of any hybrid system, like your Prius, is that it performs quite well when driven normally, and even better when only modest care is taken. If you want the big numbers though, you have to work on your skills and techniques.

eman5

Is there any reason or benefit to downshift to "B"? I haven't found any explanation for this transmission setting in my owner's manual.

PIREP: Only 450 air-conditioned, 50-50 city-highway, carefully driven miles so far, and only 20.1 mpg. Pulling to the right. Great car overall. Hoping the mpg will improve...

wwest

Enables engine compression braking, sort of a low power "jake brake" if you will.

Typically used as a way to save brakes from overheating coming down a steep mountain pass...

But be extremely carefull using it on wintertime adverse roadbed conditions, reserve your front traction patch for directional control, NEVER braking!

rx400_owner

Eman, It shouldn't be pulling. There was a post a while ago by someone who had trouble with that (I think it was this board but it might have been another one I read). It turned out the mechanic doing the prep had gotten the alignment wrong. The owner was told that the settings are different between the RX330 and the RX400 so the mechanic had made a mistake.

On mileage, did you reset the mileage meter after you got the car? The prep leaves it with a fairly low reading. Unless you are only making very short trips or have something very adverse going on, the mileage should be better than that even with AC.

You would only use B on a long down grade where the regenerative braking wasn't enough. B engages engine breaking - kind of similar to going to 2nd gear on a conventional transmission except from what I've heard, the effect isn't as strong. For instance I expect to use it coming down the Sierras or the Grapevine in LA.

eman5

Yep, I've reset the consumption meter several times. I'm taking it in to get the alignment and mpg checked (if it doesn't improve) when the license plates arrive. Will post f/u.

Thanks to you and wwest for "B" info. Does B add any juice to the battery, or does it only affect the ICE?

wwest

Basically the battery will still be charged using regenerative braking but not as fast as otherwise. Just remember to take it out of B afterward or recharging will be low longterm.

rx400_owner

"B" only affects the ICE and it will reduce the amount available for regeneration. I assume if you step on the brake while it is in B you will get engine braking plus regeneration plus, depending how hard you are braking, the brake pads.

If you just coast down hill with B on, I don't know if you get engine braking plus regeneration or only engine braking - I haven't had a chance to try it yet. It should be easy to tell if you are getting regeneration. The generator produces a slight whine and the power meter goes into the negative region.

I expect some time this summer I'll get it up into the mountains and get a chance to try out the B function.