Mercedes 300D Suggestions

fezo · January 2009

That's certainly a good first guess. You got a temperature gauge in that? If it barely lifts off the bottom of the gauge it's probably the thermostat stuck open.

benzsilver · January 2009

I once had this problem on my 300 cd. There is an electrically-operated valve between the battery and the back of the rockerarm cover.You can identify it by its water hose connections. the technician took it apart and either cleaned it or put a kit in it. he said it corrodes with time and does not open to allow hot water to flow through it to heatercore. Good luck, as I believe you can easily solve this problem. Had the technician not shared and explained the process, I would have been puzzled too.

lwoolard · January 2009

Thanks for the information. I am changing the thero. tomorrow and I will check out the valve and see what i can find. The temp on the car does run cold and the temp does not change when you turn on the heat setting. It also takes it a while to warm-up.

burdawg · January 2009

The servo valve is the part your thinking of. It's a black plastic box with electrical connectors and hoses (vacuum & water) connections to it. On climate control II it controls everything, heat, cool, vent outlets, etc. The buttons on the control panel override it to some extent, but your dead in the water without it. It usually can't be fixed, and is costly to replace.
It may not be your problem, it's possible something else is. MB has a good manual for the climate control, unless your very familiar with the system you really need it.

lwoolard · January 2009

OK, I changed the thermostat. The one that was in there was actually broken and turned sideways. So It did need the thermo. However it did not fix the heat. I think the problem is the auxiliary pump. If I am correct, this part pumps the water through the servo and into the heater core. The water is getting to the aux pump and no farther. Now I do not have the time to order another one because it is going to be 15 degrees F here tonight. Is there anyway to bypass the pump so I can get heat until I can get the part. Any help is greatly appreciated. :confuse:

burdawg · January 2009

The auxiliary pump only comes on below certain temperatures (I don't recall what) and doesn't block the flow of hot coolant to the system, it only assists. Quite typically they go out and you don't know it. I doubt if that's the problem, since it would still put out heat even if the pump was bad, just maybe not well in real cold conditions. Remember that these were designed in Germany where cold weather is more of a factor than hot weather. There's a sensor mounted to the servo valve (on the bottom?) that senses the temperature of the coolant and keeps the climate control off until the coolant reaches the operating range, that is possibly your problem, but 9 out of 10 times the problem is the servo valve. Otherwise I would look at the control assembly (the buttons on the control panel), since vacuum leaks can occur there also. Vacuum is real important with this system, and unfortunately there's potential leaks all over the place in a car this old. I had a 1980 280se, and the climate control along with the central locking system were the things that kept me busy on it the most. I can't even guess how many times I had that climate control manual out. The person that bought it from me got a good deal, since it included all of my notes in the margins!
Sorry if I'm a little fuzzy on some of this, but it's been a long time, and I sold my MB manuals some time ago since mine is long gone.

lwoolard · January 2009

Thanks burdawg for the info. I don't know much about these servos only what I have managed to find online. I did see that there is a heater valve underneath what they call the ornamental grill, which is under the windshield wipers. It looks like it is beside the wiper motor. Now I know that hot water is getting through the Auxiliary water pump(the water line to the pump is warm and the bottom of the pump where the water go through is warm) and the lines to the servo(small hose that goes from the Aux water pump to the servo) seem to be warm as well. So here would be my next question. Is there a valve in the servo itself that allows hot water to get to the heater core or is that valve( the one that opens to allow water to go through heater core) actually under the ornamental grill beside the wiper motor? I hope this isnt to unclear. Please any help would be great.

benzsilver · January 2009

sounds like you are on the right track. hot water is getting to the distribution point, however the piston that allows the water to pass through may be stuck due to 1. corrision, 2. lack of electrical power to the unit, a).no power to unit itself b) no power to the switch that actuates the mechanism it self. I would go to the fuse box first. all fuses are identified and one can tell which fuse belongs to what. if you dont recognize a description, that is probably the name of the part thats causing the problem.no pun intended. otherwise raise the hood of the car, have someone get in car ready to operate all controls concerning HVAC , with engine idleing you observe the valve that i originally identified fo you. if you see now ch ange after each adjustment is made then the valve is defective due to one or more of the reasons mentioned above. good luck

burdawg · January 2009

If it's like my 280 was, and I'm about 99% sure it is, the valve is the bottom of the servo valve assembly. You can take the top off of the servo valve assembly and watch it turn back and forth while it's being operated like benzsilver said. I wouldn't try to take the valve apart. If you turn on the defroster the valve should turn to max heat (and the A/C compressor should be on if it's working), the other control positions may make it turn to lesser heat depending on the conditions. Check the vacuum connectors where they mount to the valve, if the rubber has dried out it may be leaking there.
I can't stress the need for the factory manual enough.

ryan77300d · January 2009

The part you're looking for is the mono valve, a component on these Merc's that fail like they're going out of style.

You can check the existing valve for function with a multimeter. Infinite resistance and it's pooched. They aren't too too pricey from the dealership, so it would be very benificial to just replace the mono valve and not have to worry about it.

burdawg · January 2009

I thought the mono valve was on earlier Climate Control 1 cars?

lwoolard · January 2009

That is correct the monovalve is on the climate control 1 cars. But I did get heat!!!!!!!!! This is how I got it. The servo is not working as I could not hear it at all when engaging the heat. But my servo is not leaking at all so all I did was buy a connector and tied the line coming off of the Auxiliary water pump to the line directly in front of it.(looking from the passenger side of the car it is the line on the right side of the servo) This bypassed the servo and i got instant heat. Now I only have heat, which is ok for the winter, so when it warms up, I'll open up the servo and see if I can free up the heater valve. If not I quess I can go back to the original hook-up or buy a new servo. Thanks for all your help.

By the way the fix only cost me $3.82. :shades:

lwoolard · January 2009

Another problem that I have noticed with the cold weather we have had is that my 1979 300sd has a hard time starting. I changed the glow plugs and no change. I went to diesel giant and learned how to test the relay and related things. I found out that my 2nd and 3rd glow plug are the only two working. The problem is in the wires. My question is does anyone know where I can buy a new glow plug wiring harness? I can not find one anywhere online. Thanks.

lwoolard · January 2009

Hi All no need for the wiring harness as I took mine off and replaced the glow plug end loops as the ones on mine were almost half way broke off. She seemed to fire-up well after I got everything back together. But the glow plug light still blinks for a while after she starts. Not all times but mostly when I first start her up, any suggestions as to why? The battery is new, the glow plugs are new and the wiring is good, also there is 12.5-13 volts coming off the glow plug relay so it is fine. I love working on this old beauty!!

brillanze · February 2009

I am having much the same problem. I have a 1983 300D (odometer was stopped at 317,000 mi) that I bought at an auction several years ago. I have driven it like crazy and done very little maintenance. However, I have noticed that I have a hard time getting it going in the mornings; it starts up fine, but does not respond when I put it in gear until it has been warmed up for at least 15 minutes. Sometimes if I re-start it, it runs better. But it runs very rough (especially after stops and up hills) until it really warms up, then it is fine the rest of the day. I suppose that I should at least change the glow plugs and probably change out the transmission fluid and filter. (I haven't done either in the 3 years that I have had it). However, I already have a running tab of about $4000.00 to restore this car if I want to keep it--I am worried that I am pulling low compression and will need engine overhaul -which I would not want to invest in this car. Any ideas? Shoud I count my lucky stars and part this car out? :confuse:

hpmctorque · February 2009

I'm not one for parting with a car early, but in this case, yes, I'd part with this car now. It's time, in my opinion. However, I consider Shifty and Fintail to be the real authorities on your 300D, so I'd defer to their suggestions.

socaltrafficas · February 2009

Hey, what are you complaining about, it starts, it likes to be warm (all old cars and people do), and you've hardly touched it. Maybe get the valves adjusted but if it's not burning a ton of oil (more than 1 quart every 3k) then let it warm up. Old cars are like and old wife, tired, saggy and slow to start, sure a new one would be fun but it's going to cost you!

fintail · February 2009

I don't know a lot about diesels, but if he simply wants to do a glow plug change and a tranny flush before making a decision, I'd say let him do it, those aren't very expensive fixes. A miled up W123 isn't going to be worth a fortune in parts anyway, so I think he should drive it until it has some kind of catastrophic failure.

Mr_Shiftright · February 2009

Sure no harm in glow plugs and trans service and a valve adjustment. My guess is that you need new injectors. They DO wear out you know.

You might try some toxic injector cleaner---not that whimpy stuff off the shelf, ,but something like BGK-44. Ask a truck diesel shop to recommend something and if he hands you a can while wearing a HAMZAT suit, that's the stuff you want!

But if a $250 investment does no good, definitely bail out of this car. You can buy these very cheaply right now due to the drop in gasoline prices and the apparent tailing off of the "veggie oil" craze.

rnugent · February 2009

I am looking for a (cheap!) 3rd vehicle, for hauling stuff from Home Depot, towing a small (less than 1000 lbs.) boat, back-up for the main vehicle as the 2nd (a Crossfire) won't fit all 3 family members, etc. Live in coastal Virginia, so, winters are mild, but, summers hot & humid.

Looking at 2 300 TE's, one w/about 100K and another w/about 145K. Questions: how can I tell if it is 4Matic? One claims to be, but, there is no badge that says so...is there a gage, controller, etc., in the instrument panel that tells me? If RWD, how to tell if it has limited slip diff, which is apparently an option on these?

Both seem to sag at the rear end, which could be problematic for hauling stuff...is this just a matter of replacing shocks or is there a likelihood of more involved repairs?

Any other items which I should have mechanic look at when considering these vehicles? Used to have a 300D sedan (1977), so, I am not a 'virgin' when it comes to older MBs.

thanks, ray

Mr_Shiftright · February 2009

You'd don't want a 4Matic. You don't even want to park on a street near a 4matic.

fintail · February 2009

If there's no badge, it's probably not a 4-Matic unless the panel was painted and the badge not replaced or something. I'd run it through a VIN decoder to be sure.

The sagging rear end is probably a defective load leveler.

As Shifty says, you probably don't want to mess with the early 4-Matic. Failure is almost guaranteed. The system wasn't done right until the 1998+ models, but those have their own set of issues.

rnugent · February 2009

OK, I get the 'no 4Matic' message. Don't have to hit me over the head w/a 2x4. I would be happy w/RWD as long as it has limited slip differential. Anyway I can tell if it has this feature before taking it to my mechanic? He will charge me $95 to do a full pre-buy insection, which is fine; however, I don't need to do that if there is no limited slip differential/traction control.

Thanks, Ray

Mr_Shiftright · February 2009

jack up both rear wheels. Put trans. in neutral (or put car on a lift). Spin one rear wheel. If the opposite rear wheel spins in the SAME direction, it's a LSD. If it spins opposite, it's not.

Sorry to beat you over the head, but failure to hear the 4Matic message can result in financial disaster for the buyer, so I wanted to make that pretty clear.

fintail · February 2009

I don't know how garbled the results will be, but run the VIN through This Decoder and it should tell you how the car is equipped.

rnugent · February 2009

Well, I dithered too long and the non-4Matic sold. Called last night to make arrangements to pick it up for my mechanic to look at and the seller said somebody bought it at lunchtime. Drove a couple of hours to see it, took one look and bought it on the spot. It was in very good condition exterior and interior, w/99K miles. There just was no record of where it had been for 11 years and I was puzzled by that, plus, the hvac blower didn't work, which meant I couldn't tell how well the ac system would work before making the purchase. I spent a lot on my 300D on the ac and never really got a good result.

I have a line on a couple '95 E320 wagons, both non-4Matic (See? I learn...) Any surprises about which I should be aware? Thanks for any info...

Raymond

Mr_Shiftright · February 2009

Well being aware of a malfunctioning HVAC system was a good idea---that can set you back thousands of dollars.

I'd say HVAC, engine or systems warning lights and various electrical glitches are what you should be keeping a sharp eye for. If I were buying one of these older Benzes, I'd take a long long test ride and I'll play with every knob and switch over and over again.

fintail · February 2009

That's the last year for the 124, those are good cars. The 124 is widely considered the last series to be built to a standard rather than to a cost.

As Shifty says, HVAC can be problematic...I think those cars can have wiring harness issues too. Window switches and regulators can fail - not grossly expensive, but annoying. As with any automatic of that age, proof of maintenance is something I would look for.

lwoolard · February 2009

Hi all. I just purchased a 1984 300dt with 206,000 on the clock. The car was garaged all its life and maintained perfectly as it is a two owner car. The previous owner bought it at 60,000 miles and owned it for 16 years. It sat in there garage for 2 years. The day I looked at it, it was 19 degrees F out with snow on the ground. I put the battery out of my 1979 SD in it and it started in not even one second with no smoke and did not shake rattle or anything ran perfect. I gave the owner $1,000 for it and drove it home. Now is the fun part. The only problem that I have is the door locks. They had been unhooked because they had quit working properly. There is no vacuum at all going to them but the passenger side front and the driver side rear keep locking when you pull the outside handle to open the door. I am ok locking and unlocking manuely but why are those two locks doing this. You unlock them manuely and you may be able to open the door once or twice then the lock goes down on its own. This only happens on these two locks, any answers would be great.

Mr_Shiftright · February 2009

You need to pop the panels off and see what's up in there. Maybe they disconnected not just the vacuum motors but also the lock linkages. Just unscrew the arm rest, the surround on the door pull, and the chrome surround on the door lock (on the edge of the door as you open it), then unscrew the lifter knob, pop off the panel and lift UP and it's off. Simple. Then you can observe what is going on in there.

It's not a good idea to disconnect the vacuum system. If it leaks, your engine won't shut off and your car won't shift correctly.

These little vacuum motors are rebuildable and you can get kits for them for not much money.

It's great that the engine starts right up. If a Benz diesel cranks and cranks before starting, that's usually a very bad sign.

lwoolard · February 2009

Thanks for the quick response I will do that. Yes it started right up as if it had already been running but I know it had not. I think its going to be a good car. It is the best one I have owned anyway. I did take the panel off the front door and there was a black plastic piece up at the top of the door down from the the stem that sticks out of the door, that the knob screws on. This piece seemed to be broken but i could not extract it from the door. I don't know what it is for it did not look to have any purpose at all. Any suggestions?

Mr_Shiftright · February 2009

I dunno. It's been a long time since I've been in one of those doors.

sfactor · February 2009

Hi -
Does anyone know what is the normal braking distance (from 60 MPH) for the 1981 Mercedes 300 Diesel?
Thanks -

Mr_Shiftright · February 2009

phew, that would be hard info to find---you'd have to call up Road & Track, speak to the librarian, and ask her if they have reprints of a road test from that year.

I can tell you, from owning two of them, that they stop pretty darn well for a big barge. I had to put mine "on its toes" a couple of times and it stopped as well as most contemporary sedans do today.

So if you're asking because yours isn't stopping well, then you're right, it's not.

Mr_Shiftright · February 2009

RE: Benz door locks mysteriously locking --

Well since you have the panel off, why don't you duplicate the situation where the locks misbehave, and watch what's going on in there?

fintail · February 2009

Is this for a W123 or a W126? I have some period info on the 126 at home I can look through if that's what you need.

lwoolard · February 2009

I did and it looked as if the vacuum element was sucking it down, I did'nt want to unhook the linkage as I think i will try to fix the system properly.

Mr_Shiftright · February 2009

Okay so the vacuum is NOT disconnected. I believe the driver's door has a master vacuum switch (controls all the other doors), so if that is malfunctioning, it could be locking the doors AS IF it thought you were turning the key in the door to the "lock" position?

Does this make sense? At least it's one possible cause.

sfactor · February 2009

thanks!

jameslei · February 2009

My workhorse of a 1982 300TD diesel engine is so keen to work that it won't switch off and I can walk away with the ingnition key in my hand. To get the engine to stop I have to lift the hood and hit a red button marked STOP on the accelerator linkage. Is there a simple way to solve this problem? I really don't mind that the doors have to be locked by pressing down the buttons in the 4 doors
because the vacuum-operated(?) system is kaput. I though that perhaps (with luck) there might be a rubber vaccum tube located somewhere and I could simply ligature it off so the engine will stop when I turn the ignition key to 'Off'. I'd appreciate any advice,
Many thanks,
Jameslei

zadams · February 2009

your engine will not stop BECAUSE your vacuum system is leaking. the vacuum system controls a lot of things including the fuel shut off, transmission functions, door locks, etc. which you may or may not know but just in case to clarify. you should look above your injection rail for a circular-ish metal object that has two vacuum lines going to it. one should be behind (windshield side) of the object and slightly difficult to access. check that line behind the shut off to see if it is disconnected. you have to find the vacuum problem or your tranny will shift rough, your fuel will not shut off with the key, your doors will not lock. do you have access to the online library? if so, you should be able to get a vacuum diagram and check your system for missing lines or leaks/disconnections. overall though, the system is way too complicated to solve over text. If you hear a air leaking sound when you are inside the car it may be as simple as one of your door locks leaking.

jameslei · March 2009

Thank you Zadams! Everything else seems to work OK except for the doors not locking when the driver's lock is closed and, of course, the engine not turning off.
How does one access the "Online library" you mentioned? Many thanks once again. James.

lwoolard · March 2009

Hi all my 1984 300d has just started giving me a little grief. There is a very loud scratching clanging scrubing sound coming from the rear passenger wheel. It is so loud that I can hear it inside the cabin of the car with the window closed. It is so bad that I am afraid to drive it. I took off the wheel and everything looks good and tight. What could this be? :sick:

Mr_Shiftright · March 2009

Possibly rear axle CV joint. If the boot is split open, then it's probably no good for sure. They are difficult to check without pulling them off, washing them down and inspecting them.

lwoolard · March 2009

The boots look to be in good condition. Could it have something to do with the emergency brake, It does not work.

jameslei · March 2009

Hello. I had a similar problem with my 1982 300TD passenger side rear wheel. AIt turned out that a bit of metal (maybe from the brake shoe) was rubbing on the disk. But I only found that out when I paid to have the shoes replaced - I had earlier taken the wheel off and could see nothing wrong. Good luck!
James.

Mr_Shiftright · March 2009

Oh sure you didn't mention that before!

lwoolard · March 2009

Sorry :confuse: I wasn't thinking correctly at the time. From all the noise it is making I am just happy that the rearend is still on the car. Hopefully it will warm up enough tommorrow that I can check out the emergency brake. Bye the way Shifty I have read alot about bypassing the egr valve and the 3/2 way valves on top of the valve cover. Is that a safe move? Some said they did it to help with vac leaks from the 3/2 valves.

burdawg · March 2009

If it's like the earlier cars, and I think it is, the emergency brake shoes are separate and are inside the center of the rotor on the rear wheels. You will have to remove the rotors to get a good look at them. If the e-brake isn't working you could have a broken part rubbing inside the center of the rotor.

Mr_Shiftright · March 2009

I never heard about doing that---news to me. Seems to me that vacuum leaks would be easy enough to seal. I never had any trouble with vacuum leaks on my diesel Benzes.

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