Regular Plus vs Premium Fuel - Which is really less expensive?

mwhunter1mwhunter1 Member Posts: 5
edited March 2014 in Toyota
I recently read where a company had finished a long term test with the FJ which ended with around 18,000+ miles on the odometer. "Combined" MPG during their driving came in at 17.3 MPG. I know that some people will be able to get 18-20, but for this post, let's stick with their 17.3 MPG for the purposes of seeing what's better: Buy mid-level gas and try to save some money but lose commonly acknowledged 2 MPG by using a lower octane fuel, down to 15.3 MPG, and suffer performance; or buy the more Expensive but recommended Premium, and get 17.3 MPG.

I priced gas recently up here in the Northwest and Regular Plus was $3.59.9 a gallon while we were being soaked for Premium at $3.69.9 a gallon.

Now if an FJ driver bought $100 worth of Regular Plus @ $3.59.9, he would end up with 27.78 gallons of gas, and at 15.3 MPG, would be able to drive 425 miles. That equates out to .23 1/2 cents a mile.

But if an FJ driver bought $100 worth of Premium @ $3.69.9, he would end up with 27.03 gallons of gas and at 17.3 MPG, would be able to drive 468 miles. That equates out to .21 cents a mile with the benefit of added horsepower and probably better operating conditions for that expensive engine.

If my numbers are right, it doesn't seem to make sense at all to run anything but Premium in the FJ's as in the end, you go more miles for less money.

Am I nuts or do you agree?


  • tidestertidester Member Posts: 10,059
    I think the error bars on that 2 mpg are probably much larger than the per mile cost you calculated! Also, people don't usually buy gas by the dollar (though that may change as we head toward $5/gallon). They buy it by the tankful.

    If I recall correctly, the capacity of the FJ gas tank is about 19 gallons so, using your numbers, you would get about 290 miles on a tankful of regular plus while being able to squeak out about 329 miles on a tankful of premium.

    Now the average car owner drives about 38 miles a day. Notice that 329 mi - 290 mi = 39 mi which means that you would be driving to your gas station for a refill about one day sooner when you use regular plus. Surely, the cost of driving to and from the gas station and the value of your time should come into the equation as it amounts to about 8 extra trips for fill-up every year! This is based on 1 tankful a week for the premium. :)

    Having said that, those costs aren't the ones you should be concerned with. I recommend following the manufacturer's recommendations for fuel since that is what the engine is designed for and other performance and engine durability issues arise when deviating from those recommendations.

    tidester, host
    SUVs and Smart Shopper
  • mwhunter1mwhunter1 Member Posts: 5
    Hey Tidester,

    For the purposes of my post, which was to challenge the common assumption that some owner's think that it's "cheaper and better" to run Regular fuel in the FJ vs the recommended Premium, I didn't think that what container (fuel tank) it went in would be important; More the total dollar amount paid for how many gallons of fuel consumed to propel the FJ for a specific amount of miles.

    I think the numbers I came up with easily show that it makes more sense to fill the FJ's tank with Premium and be able to travel more miles for less money than a driver would by running Regular fuel, under the assumption that it would be cheaper. It would not.

    When you say "I think the error bars on that 2 mpg are probably much larger than the per mile cost you calculated!", what exactly do you mean by that? That if a person uses lower octain fuel than the recommended Premium, that the MPG lost would be greater than 2MPG? If so, that makes my point even stronger.

    Having said that, I totally agree with you that drivers shouldn't try to circumvent the owner's manual and find a cheaper way to operate a vehicle they paid $30,000 for. Toyota didn't pull the requirement for Premium fuel for this engine out of the air. If they didn't know what they we're doing, none of us would probably buy their vehicles in the first place.

    Of the 4 Toyota dealerships I went to asking specific questions about the FJ and the Premium fuel requirement, I found it amazing that most salesman I talked to weren't aware of the FJ/Premium fuel requirement, but every 'every' salesman I talked to who was aware of the Premium fuel said that "...their Service Center people said that it's OK to run regular fuel in the FJ". Maybe their Service Center said that and maybe they didn't.

    And sure it's "OK" to run Regular gas. If you want to run your engine on a fuel it wasn't designed to run with, suffer performance and MPG problems, pay more per operating mile, and eventually possibly pay for any damage that long term use of a low octain fuel may cause to that very expensive engine.
  • kawagumbykawagumby Member Posts: 2
    Another viewpoint;
    lletin and my own owners manual that both state the FJ V6 will run on regular fuel. I have also read that the Tundra V6 uses the same engine and does not have the premium fuel filler note.

    It is likely that in order to reduce detonation during sustained open throttle conditions, the premium fuel is necessary, this engine utilizes a fairly high compression ratio. This would affect the horsepower ratings that are used to advertise one vehicle vs another brand when under comparison. The horsepower difference is less than 5, as I recall, and would likely only come into play at higher rpm's. Premium vs regular fuel should not impact fuel mileage if there is no detonation, or other kinds of combustion chamber flame propagation anomalies, IMO. This, of course, assumes that the engine is not subjected to heavy loads and that quality regular fuel is used, not the less desirable fuel that is sold by independent merchants. I use 87 octane in my FJ and it gets over 20 MPG always, and I've yet to hear any detonation (But I have also yet to drive at higher altitudes pulling a trailer, etc. - at which time I will use higher octane fuel).

    I suspect that the referenced FJ used in the long term test would tend to driven much harder, as would be normal for such reviews. If so, the difference between regular and premium fuels would be much larger than would be experienced by most daily drivers.
  • steverstever Guest Posts: 52,454
    What about fuel types & gas mileage? discussion.

    It's not limited to the FJ, but there's more food for thought to chew on there.
  • tidestertidester Member Posts: 10,059
    When you say "I think the error bars on that 2 mpg are probably much larger than the per mile cost you calculated!", what exactly do you mean by that? That if a person uses lower octain fuel than the recommended Premium, that the MPG lost would be greater than 2MPG? If so, that makes my point even stronger.

    No, I was suggesting that if the error bars are large enough then the the "real" difference in mileage between the two types of fuel would actually be smaller and, thereby, any savings would be somewhat exaggerated using the 2 mpg figure. We do know that even slight changes in driving behavior, road conditions, tire inflation and so on can often result in more than a 2 mpg benefit or penalty. It's difficult to get precise figures for gas mileage that take all those factors into account so the uncertainty in those figures probably matters.

    Nevertheless, you do raise an interesting point!

    tidester, host
    SUVs and Smart Shopper
  • oy812oy812 Member Posts: 3
    I just recently bought a 2007 FJ Cruiser and am getting only about 200 miles to the tank. I live at the top of Maine where the average speed is 50 miles an hour. I have tried both high and low octane fuel and it doesn't really seem to make a difference in how long my tank of gas lasts. That is about 10.5 miles per gallon, or 1 fill-up per week. I am just wondering if there might be something wrong with my FJ. It has 12000 miles on it and the TRD rims with BF GoodWrench T/A tires. Looking for some answers if anyone can help me out.
  • oy812oy812 Member Posts: 3
    This was an EXCELLENT review of high and low octane affects fuel economy!
  • mwhunter1mwhunter1 Member Posts: 5
    I was just reading the Owner's Manual for the 2008 FJ, and at least in 'that' manual, it says the required fuel for the FJ is 91 octane.
  • jcostajcosta Member Posts: 1
    I have a 07 FJ auto TRD and have only run three tanks of fuel two of which to report on. I have registered on First tank $45.15 @ 13.18 gal 253 miles for 19.2 MPG. Second tank was $45.50 @ 14.31 gal 278 miles for 19.42 MPG. I run mostly back streets 45 mph tops. When I run on the highway 70 to 75 mph. Reg gas 87 or 89
  • fhrabetinfhrabetin Member Posts: 34
    Keep in mind that this vehicle has an "S" shaped fill tube which confounds most auto fill pumps in Oregon, premature click-off. A very slow fill can help this. When I top off I can add up to 3 gallons, +/- 0.5 gallons. Ambient air, temp of vehicle gas tank, how cool is the gas storage tank can all confound this. I'm not sure I've covered all the variables.
  • steverstever Guest Posts: 52,454
    They let you pump your own gas in Oregon now?
  • mnfjhuntermnfjhunter Member Posts: 3
    I own a 2007 Fj with manual trans. I use 87 octane fuel and average just under 15mpg. I never gained more than 1 mpg ever while using the 91 octane fuel. In the winter my mileage was only 12-13mpg. I have the TRD Rims with BFGoodrich T/A tires on it as well. Roof rack,skid plate, the works. Everything an TRD edition would have other than the paint and exhaust. These reports of people getting over 20mpg is B.S. I think. I have to fuel up after only 250 miles tops. I could squeeze another 20 miles, but I don't want to be stranded on the side of the road. I now have 25,500 miles on mine. It drives great in the Minnesota winters. :confuse:
  • tnbluefjtnbluefj Member Posts: 3
    New to this forum. Just wanted to say I have an '07 FJ, bought in Feb of '07 - I now have almost 25,000 miles. Own a home in TN and in FL so do a lot of Interstate driving. I only use REGULAR fuel and always get over 20 mpg hwy. I just returned to FL from 3 weeks in TN and my best mpg was 24.77. My average with 5 tanks was 22.28. I keep my tires aired up, air filter is a K&N, no luggage rack, no other mods. I usually drive the posted speed. On I-75 will drive 72-73 mph., over that and mpg will drop considerably. I do not quickly take off from stops and try to be careful with accelerating into traffic. I have tried several tanks of premium and noticed no difference in my mpg. So I know you can get decent mileage per tank, but you just have to pay attention to your driving habits. And if it makes any difference, I am a 52 yr old female.
  • sparklemahnsparklemahn Member Posts: 11
    Just picked up a brand new 2008 FJ 6 speed stick. The extended owners manual specified 91 octane gas. Mobil has 93 and 89, so if I fill up with the same amount of fuel but switch off between 89 and 93 octane, I will average 91 octane. If the manufacturer calls for 91, you should use 91! Do not complain later if you have engine trouble, ok?
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