Mercedes 300D Suggestions

amonra22 · June 2005

Mr Shift right,
took my 300dt into the mechanic for a valve adjustment and with that a new valve cover gasket, had waste gate hoses replaced, and vacuum valve replaced. also new over flow hose. the loss of power on any kind of hill is now worse than before, it feels like you are dragging an anchor behind you. Was driving thru the Caldecot Tunnel and while i was driving thru Orinda/Moraga up the 24 I was at 35mph with constant pressure on the gas peddle. Question, does each cylinder have a fuel injector or is there only one? And, do you think that if I replace the injector should I also replace the injector pump?

Mr_Shiftright · June 2005

Geez, I don't see how it could be WORSE by doing those things properly.

Why don't you take the car over to European Auto Repair in San Rafael---they know what they are doing. You can't be replacing things like an injection pump without really diagnosing things, that's way too expensive for "guessing".

koolfrog · June 2005

I plan to tow an utility trailer behind my 300D : What is the towing capacity of this car ? Where can you buy a hitch at a decent price ( not much help on the WEB !) ? :confuse:

turbomaster · June 2005

Hey i have a 1987 300D Turbo. I bought about 10 years ago, it now has about 200K miles on it. I was wondering, does anyone had any advise on how i could improve performance on my car? how about a blow off valve? would that do more harm than good? Thanks

Mr_Shiftright · June 2005

I'm not sure but I would think not very much....probably no more than the weight of a few passengers. I presume you aren't going to weigh the trailer down very much. This is after all, just a passenger car with less than 100 HP. I also bet the towing capacity is in the original owner's manual if you have one.

There are speciality shops that can fit you with a hitch I think. You should try your local Yellow Pages.

Mr_Shiftright · June 2005

Your car should perform decently as is....short of radical modifications I can't think of much you can do to an old turbo diesel....maybe modify the turbo for more boost but as you know, that is risky on an old engine, as any deficiencies in head gaskets or valve seating or piston ring sealing will be amplified with more boost.

Maybe you could rig up a cold air intake, use synthetic oil, inflate your tires, adjust the valves and time the injection pump---that might give you a little boost and better throttle response.

turbomaster · July 2005

Thanks for the tips

Mr_Shiftright · July 2005

Well I'm not a diesel expert so maybe some diesel freak knows some tricks, but I just can't think of any that are safe or economical.

benzboy1 · July 2005

My mechanic told me I had severe blow-by. I went through the car, changed vacuum hose, oil, transmission fluid, and any other part could find to change. My blow-by is not so sever. Can you turnaround blow-by?
I also think the timing is off. My mechanic tells me it to much trouble with a car that has Sever Blow By. And that I need a new engine. :shades:

Mr_Shiftright · July 2005

No, blow-by is a terminal disease. It is caused by worn piston rings. YOu can test the severity of the wear by doing a cylinder leakdown test or compression test. You need special equipment to do this on a diesel.

Injection pump timing doesn't "go off" very easily, so I'm dubious about that diagnostic. Only a real expert should ever attempt injection pump timing.

tijolo · July 2005

hello
I recently bought a 1978 mercedes 300D with 80,000 miles. When I am driving on the highway for a while and then get into stop and go traffic my oil pressure drops down. Most of the time my oil pressure guage reads at the top, 45 lbs per sq in. When it is problematic it will drop down to around 20. The pressure only drops when the car is stopped and in gear. I have been dropping it into nuetral and that has seemed the take some of the load off of the engine.
One other sign of oil pressure issues is the the air filter has oil that has been pushed up into the filter housing. It drives extremely well and has no problems. Is there anything that I can/should do to help this old mercedes along?
thanks
jonathan

Mr_Shiftright · July 2005

All that sounds like a perfectly normal 300D to me. That's what they do, it's fine, as long as your oil pressure is near the top when you are on the highway.

As for oil in the air filter housing, you just have to keep that clean. Old diesel engines are kind of dirty nasty things or SEEM to be--ever notice that your engine oil is dirty ten minutes after you've changed it?

New diesels are way more sanitary.

Again, just wipe out the housing and keep those air filters fresh in there by rotating them away from the oil scum. I used to change my oil every 3,000 miles and the air filters once a year regardless.

telordd1 · July 2005

I have an 83 300D. The door locks work but about every 5th time I shut off the car, the door locks will not work. Also, the engine won;t shut down every 5th time as well so i have to pop the hood open and manually shut down the engine. Where do I start? My mechanic is orering the part to fix the engine shut off..is there a possibility this will aslo fix the door lock problem?

Mr_Shiftright · July 2005

You have vacuum leaks somewhere is the problem. From what you say, it must be a big leak since you are knocking out the door locks AND the engine's normal vacuum-driven shut off valve.

Diesels have no ingition so the only way to shut them off is to shut off the fuel. Benz does this by engine vacuum....so, vacuum loss = engine stays running.

Replacing the vacuum shut off switch may or may not cure your problem, depending on whether the switch itself was causing the vacuum leak or was merely affected by the vacuum leak.

If that doesn't do it, then you have to go on a "hunt" for the vacuum leak.

richie123 · July 2005

hi i have a problem with my 1974 mercedes 300 D. Everytime i try to start it i cant. I have to put a special liquid ,my friend gave me, that goes in the air cleaner. Somebody told me that it was the gas pump but i havent been able to find it anybody knows where it is?

Mr_Shiftright · July 2005

Once you use the staring fluid, does it run then?

If it does, then I would suggest that the first thing you need to do is probably replace your glow plugs if this hasn't been done in the last two years.

And you'd better be careful with starter fluid in a diesel.

If it won't start even with starter fluid you might want to have a compression test done to see where the engine is at.

richie123 · July 2005

thanks Mr_ Shiftright for ansewring my question but why you told me to be careful with the starter fluid isi it bad to use it in a diesel?

tijolo · July 2005

my dash lights are out in my '78 300D. Maybe its a fuse...but my blinker lights shine bright on my dash. It seems like a simple repair...but I don't have the knowledge yet. Also, would you suggest a repair book. Thanks in advanced.

zero3k · July 2005

You may want to check the rheostat (the dimmer) contacts. Try shorting them with a paper clip or wire (so that the two "pins" on the back of the dimmer are connected via the wire.. this is the setting for "full bright".) If this does not work, and your center console lights are out as well.. then one of the solder tracks most likely came up. Take out the dash panel, and break out the multimeter.. testing for connectivity, and looking for any burned up tracking. If you find any, re-solder, and you should be on your way!

Mr_Shiftright · July 2005

Starter fluid is a great solvent for washing oil off cylinder walls, and also highly explosive. Too much of it could be harmful, yes. If it doesn't work after one or two good squirts, STOP. Remember diesels are operating on something like 22:1 compression ratios.

richie123 · July 2005

tanks Mr Shiftright for your help but i have one more question. Is there another way to start my car without usin the starter fluid? maybe with a powerfuk battery?

Mr_Shiftright · July 2005

Well diesels need strong batteries that is true but if your glow plugs are worn out you'll have a devil of a time. A diesel relies strictly on compression to ignite the fuel, and so when cold it is very unlikely that the engine can do this without the assistance of a warming component, like glow plugs.

Also, since this is a compression start engine, if any one cylinder is low on compression, this makes starting very tough.

richie123 · July 2005

thanks for all your tips they were very helpful

isellhondas · July 2005

Then, there was this guy I knew. We told him starting fluid was good for cleaning the junk out of his distributor cap.

I think you know what happened.

Mr_Shiftright · July 2005

Starting ether requires some respect that's for sure.

I have heard of the oil pan being blown off a motor but never verified that. But if you had a whole can of that stuff in the crankcase along with lots of raw gas and then you managed to find a spark....well......

Don't know if that could happen to a diesel....kinda doubt it, but you could wash the cylinders dry of oil. Ether is an amazing solvent.

stuartbell · July 2005

Our 1981 300 D with about 320K miles started smoking suddenly a few days ago.

I removed the fuel filters and found black fuel/water in the secondary. Replaced both filters and put injector cleaner in the secondary - no real improvement.

I removed and replaced the air cleaner - it was clogged and had a heavy oil deposit. Investigated further - there was some blow by - but no real oil burning - no oil needed between changes.

I loosened one injector feed at a time - looking for a non running cylinder. All five cylinders showed the same decrease in speed and roughness when loosened - and all recovered fine when tightened.

Ran thru the tank of fuel - topped off the tank - and removed the secondary fuel filter - black again. Drained it, topped it off with injector cleaner - and there is a bit less smoke - but still more than before.

Questions?

1. What do I look for now?

2. The transmission seems to shift up sooner than it used to - is the vacuum part of the shift controller? Our doors stopped working years ago and I suspect we have many vacuum leaks but don't know where to start to fix them. The breaks work fine so I feel the vacuum pump is working.

Thanks - clearly it makes no sense to put a lot of $$$ into the car - but I suspect this is something simple.

Mr_Shiftright · July 2005

What are you using for injector cleaner? If it's that $2.98 off the counter stuff, it's useless. Something like BGK44, or SWEPCO product, something SERIOUS might be necessary.

I don't know what to say about the filters but you may have a grunged up fuel tank if you haven't been using some kind of bio-cide regularly. All kinds of crap can grow in diesel fuel tanks and you need to kill it off...it's like algae, amazingly enough.

You may need to take a large fuel sample to see what you are pumping into that engine.

mateo5 · July 2005

I test drove an '85 300d today. It has some rust on the body, though I'm not all together concerned about it lest it's affecting the frame. The car has 142,000 miles on it. It drove well, except the brakes seemed a little weak. It shifted nicely and the owner said he replaced the AC about one year ago. He's the second owner. Anyway, I've never owned a deisel before, so I was wondering, when in idle, if a little shaking is normal. Like I said, the car seemed to run well. Also I was curious about the oil pressure gauge: When driving around 40 or fifty, will it be up around "3."
Those are my most basic of concerns. Thanks!
mateo

Mr_Shiftright · July 2005

Yeah some SOME shaking is normal on these older diesels. The oil pressure should PEG the needle at highway speeds or close to it.

As for rust, well if you aren't concerned, that's okay but keep in mind that this car would have to be pretty cheap if it has rust on it.

mateo5 · July 2005

that's what I'm wondering. I'm going to offer 750. It's not a TOTAL rustball or anything. A little around the base and some around the wheel wells. Also, by SOME do you mean a noticeable amount?
Can rust be repaired? Is it worth it? By the way, thanks so much for answering those questions.

mrslewis · July 2005

Hello, I have an '81 300D MB and I replaced the starter on 10/12/04. I was looking through the former owners invoices and noticed the starter had been replaced on 12/02/97 and 7/11/02. Shouldn't a starter last longer than this? It seems odd to me.

Mr_Shiftright · July 2005

Well no telling what kind of starter they replaced it with...maybe some cheapo rebuilt. Besides all that, even if it was a good starter---the starters on diesel engines work extra hard; and many people don't replace glow plugs every couple of years or keep up the batteries and so the starter has to crank and crank and really wears itself out against that huge internal compression on the diesel.

Mr_Shiftright · July 2005

By noticeable I meant "perforations"---that is, not surface rust but rust that has actually penetrated the metal and left holes. If it's that bad, no it's not worth fixing.

$750 sounds about right, that's what I was going to suggest actually.

tonys79 · July 2005

I just purchased a very nice '79 MBZ 300D with auto transmission. It runs great, but.... While the car shifts fine from 2nd to 3rd and from 3rd to 4th, it takes a LONG time to shift from 1st into 2nd gear. And once the car has gone into higher gears, it doesn't seem to want to shift back down. Is this a kickdown switch issue, or is there something else going on? Any help is appreciated.

Mr_Shiftright · July 2005

Sounds like your typical ornery 300D transmission BUT...having said that...I do believe that model has a vacuum modulator on the transmission and if this little modulator is leaking vacuum, or if any lines to the vacuum modulator are leaking, the tranny will shift funny, and in the manner you describe. So you should check for leaks in the lines first of all and if all else fails you could replace that modulator. I don't recall that it is particulary expensive or hard to do.

It's hard to say really since the transmissions in that car are kind of goofy, as compared to the way American transmissions feel, and shift.

And yes, there should be a kickdown switch, although it's pretty lazy. I always tell people to shift these cars manually up and down, since they are so grossly underpowered. You need to stretch the revs in each gear if nothing else for your own personal safety and to prevent a Range Rover from running over you from behind.

tonys79 · July 2005

Thanks, Mr_Shiftright. I'll check both the vacuum modulator and system, as well as the kickdown. Appreciate the help. Tonys79

hooptie · July 2005

quite possibly in the switch that dims the dash lights. I had the same problem and I took mine apart and cleaned it up and they work just fine now

indrit · July 2005

hi mr shiftright and everyone else. I live in Albania. recently i became owner of a 300 d automatic 1986 model and was searching for the car manual as the one provided with the car is in german and can't read. I thought it'd be easy downloading it from the web but apparently they're only offered through payment. can anyone help me download one for free?
the car is running well considering its 350k in 20 years on the road. engine's ok, (valves sometimes make that noise which is silenced as engine reaches the optimal temp). The automatic transmission works ok, had a problem with the a bursting pressure tube connected to the radiator but fixed it without serious damage. Sometimes when i charge (overcoming or hill) i see a blue fume in the back. well this might be quite usual for a 6-cylinder 3.0 L but concerned if that is caused by an engine power loss or oil consumption from worn piston rings or the fuel quality.

hail to the mercedes craftsmanship!

corv · July 2005

My 85 300D has a small leak of antifreez at the front bottom of the engine. I have looked at all the hoses and they appear to be good. Sounds like it is the water pump. I have owned it for seven years. This car has 334K miles on it. What kind of money and effort am I looking at? Thanks in advance. Ed.

Mr_Shiftright · July 2005

waterpump? That's not so bad. It's a dirty, disgusting nuts and bolt job, but you can do it. But while you are in there, on an engine with that many miles, you might want to replace every water hose that is a bit too hard or too soft, or shows any cracks, and it's also a good time to do the belts as you will have them off. Then you can go to the car wash and have someone hose you down. :P

hooptie · July 2005

I currently drive a 79 240 D manual tranny 28 M.P.G. interior is shot (horribly) as well as the body(hurts to look at it) however she runs very well (gutless) but she is dependible.I have an oppertunity to buy 3 300D cars for $1200 for all three! all are close to 200.000 miles all have automatic trannys none of them are turbo none of which run. one has an awsome body and interior (she is beautiful!) but oil pump puked on it, they say" the motor is not hurt" I call B.S. on that but I am sure that I can pice one good car together out of all three and have some parts left over. my main concearns about the 300 D are what kind of M.P.G.? how is the horse power compared to the 240 D. Is it like the 240 D on the freeway? What about putting the manual tranny out of my 240 D in it? will it bolt up? many mods? ( I have heard of many problems with the auto trannys.) if I came across a turbo car later can I put the turbo on the 300 D ? thanx for all your suggestions cal

hooptie · July 2005

by the way the 3 cars are 1977-78-79

hooptie · July 2005

by the way the 3 cars are 1977-78-79

Mr_Shiftright · July 2005

Well I don't recommend building a "Franken-car" out of the corpses of others. For one thing, you can probably buy a very decent 300D for the same price as all the money and time and extra parts you'll have in this project. For another, all you have here is worn out old parts from 3 cars, giving you, in the end, one worn out used car.

So I'd just shop for a 300D if that's what you want. Fuel mileage will be about 20 mpg city and up to about 26 mpg highway. Performance will be better than a 240D but nothing like a turbo-diesel. Comfortable cruising speed is about 70-75 mph and yes, you will still slow down going up hills. At high altitude, you'll have to get out and push. You only have maybe 85 HP there in a heavy car, so....

dyates773 · July 2005

I currently own a '79 300D. I bought it because mechanically it was sound and the body was perfect. I paid well less than $2K. The only thing I've fixed is the A/C. It now has 168K miles. I have very little money but a lot of effort into the car. Getting the A/C working, repairing vacuum leaks, changing all fluids, replacing the injectors, were all time consuming but the car was worth it.

If you want to turn three junkers into to one good car do it as a hobby not as a means of day to day driving. Look for a 300D in good condition, they're out there.
My daughter had a 77 240D that I feel was a clone to my 79 300D. Ran like a top (on flat pavement) but would not get out of its own way. Both had Auto trans that required nothing but filter and fluid changes. The 77 240D was junked after 280K miles because the body and frame was rusted beyond safe operation.

Good luck.

ronv1 · July 2005

My climate control unit only works when I turn on the defrost button. The whole unit used to work. I changed it and I'm still experiencing the same problem. Is there something that I need to check?

tijolo · July 2005

while driving out of town yesterday...70 mph. something makes a slight pop and then the temp gauge goes through the roof. I pull over, pop the hood and see that anti-freeze has sprayed all over the engine compartment. It seemed that it all came from the radiator cap. All hoses and everything else seemed fine. I was only a few miles from town so I filled it with water and crawled home. I didn't let it get too hot. But it was still much hotter than normal conditions. Same scene, antifreeze coming from the cap even though it was on correctly. Is that a typical story of a bad water pump??? Or something else? Should I have driven it home? Can I drive it a few miles to the repair shop if it needs more than I can do???
thanks

burdawg · July 2005

What did you change?

dyates773 · July 2005

The Defrost mode is the default mode for the control of the blower. It bypasses all of the components that control the fan speed.

Please give a litle more info about what component you changed. The main components are the pushbutton assembly on the dash, the Climate control servo under the hood (controls vacuum and hot water flow), and the fan controls.

Mr_Shiftright · July 2005

Doesn't sound like a bad water pump, no. You need to do a pressure test of the cooling system to see if there is a leak somewhere. The water pump could LEAK but that of course is only an indirect cause. I have seen rare cases where the impeller inside the pump breaks, so I won't say "impossible".

Once the car cools down, you should be able to run it and see if water is circulating in the radiator AFTER the thermostat has opened. Your thermostat could be stuck, too.

Overheating is a lot harder to diagnose than people thing. There are multiple causes:

coolant leak
clogged radiator
stuck thermostat
blown head gasket
cracked cylinder head (exhaust gases leaking into water jacket)
broken impeller in water pump
broken fan belt
broken electric cooling fan
bad sensors for cooling fan
crude in engine block
excessively lean fuel mixture
air blockage in cooling system
transmission cooler and radiator exchanging fluids through damaged tank
collapsing water hoses

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