1987 300TDT cranks but doesn't start and other fuel system questions
 

I changed the large canister fuel filter on my 1987 300TDT, and now the engine will not start up. The engine cranks over, and it seems as though it wants to catch but it doesn't run. I have tried cranking the engine for over ten 20 second periods (with 5 minutes breaks in between), but it never catches. I have tried cranking the engine to the point that the battery is now drained. I'm charging the battery up so I can try starting the engine again, but I am worried about draining the battery again without being able to start the engine.

In order to minimize the cranking time and lessen the air in the fuel system, I poured the fuel from the old filter into the new filter. According to the Mercedes shop manual the OM603 engine is self priming. So how long is it supposed to take for the fuel system to prime itself? Is there anything else I can do to get it to start up? :confused:

I also have a couple other fuel system questions:

There is a diesel fuel heater/thermostat after the prefilter on the OM603. On my 300TDT, the previous owner bypassed the fuel heater/thermostat. I'm not sure what is wrong with them. The price of the fuel thermostat seems to be over $130. I'm not sure what typically goes wrong with the diesel fuel heater/thermostat. Is there a common failure mode for either the fuel heater or thermostat? Is there a way to repair the thermostat? I also live in California, so I was wondering how important the fuel heater is in warmer climate?

Finally, before I changed the fuel filter, the engine seemed to smoke on a cold starts and run rough for a minute or two after which it seemed to smooth out. What would cause this? My first instinct is that the glow plugs are not all working, but a mechanic that worked on my 300TDT for the previous owner supposedly replaced the glow plugs. Any ideas? It happens regardless of the ambient temperature.

Thanks in advance,

-Steve

Pausing 5 minutes between 20 second tires is a little long. Whatever progress you make will be negated by time. Try 10 second tries 10 seconds apart. The manual says to crank continuously for a minute or something like that. I can't see how that's not asking for trouble.

You might help your injection pump along. Crack the the lines into the injectors while you crank. When fuel leaks from a fitting, tighten it and crank again. It'll probably catch before you get fuel out of all 6 fittings but I find that if I don't help the priming along for each cylinder it can take a while of rough idling before it smoothens.

Oddly enough my 2 SDs never needed priming after replacing the fuel filters.

I was tempted to bypass the fuel thermostat when it sprung a leak. In my case either the plastic end piece cum fitting or the o-ring cracked when I replaced all the fuel lines. Turns out there's an inexpensive repair kit available at the dealer that includes both pieces. I needed it ASAP so I didn't check FastLane.

My SDL is that way when it's cold. I find that going through a couple of glow cycles, leaving the key in the on position for 10 seconds after the glow light goes off, works wonders. The glow plugs are pretty new and resistance checks out. Could be any of a number of things causing the cold start roughness. Lazy glow plug, lazy delivery valve, low compression in one cylinder, etc. Check the resistance through the glow plugs and consider new delivery valve seals if they're original. Otherwise, live with it.

Sixto
95 S420
87 300SDL

There was quite a discussion about someone having difficulty getting one of these engines re-primed awhile ago and it should be in the archives. Also by dumping the old filter oil into the new filter I wonder about some junk in the filter being transfered like water in the bottom of the old filter etc. It might have dosed your pump. Should really only put clean fresh fuel oil into the new filter. Hopefully you got it running before reading this note or the archives help.

Or Diesel Purge.

Sixto
95 S420
87 300SDL

Just a note of interest. I got the idea of pouring the fuel from the old filter into the new filter from the "Mercedes-Benz E-Class Owner's Bible". The "Mercedes-Benz E-Class Owner's Bible" is written by Stu Ritter who is technical editor for the Star Magazine, as well as 25 year MBZ repair shop owner/technician. At the time I thought the idea was good, but I seem to be getting a different opinion from everyone else.

Thanks for the replies so far though.

-Steve

What model?
 

What exactly is a 300TDT? is this a Turbo Diesel Wagon? Or is it just an '87 300D? I have seen the TD designation, and the DT designation, but never used in conjunction.

SteveM.

- PS - let 'er crank. Get a good jump start and crank for 30-45 seconds.

Jetmugg,

A 300TDT is a turbdiesel wagon. The 300DT is the turbodiesel sedan. The "T" tacked onto the end stands for Turbo. Mercedes-Benz uses this nomenclature when referring to the different models.

-Steve

Thanks.
 

I did a little searching and saw others using the "TDT" designation for turbo wagons as well. I guess I just hadn't seen this before. Do the letters 300TDT appear on the back of the car somewhere?

My 190D 2.5 Turbo reads "190D" on the left of the trunk lid, and "2.5 Turbo" on the right.

The E-class wagon with a turbo 603 engine should be a very good running car. Sounds like a nice one.

SteveM.

Well, I finally was able to get the engine to start after cranking it 3 times for 45 seconds with a minute or two rest intervals. I also had to to floor the accelerator to get the IP to purge the air out of the injectors and to get the engine to run initially because it wanted to die. The engine coughed and sputtered and ran rough for a minute or so until the air was out of the lines.

Once the engine was running I discovered a new noise, the tapping sound of a valve. I'm not sure, but I think one of my cam followers may be going out. Does anyone know how long the cam followers last on the OM603? The engine has 185000 miles.

Jetmugg,

The 300TDT E-class wagon with the OM603 is a nice combo. It will be even better once I finish fixing all of the broken items on it. :) (The previous owner was a cheapskate.) The 1987 300TDT was the last diesel powered wagon MBNA imported to the US. It would have been nice if MBNA imported some W210 chassis wagons with the OM606 turbo motor, but they chose not to for some reason. A W211 chassis wagon with the CDI motor would have been really nice, but unaffordable by me.

Thanks for all of the replies,

-Steve

The lash adjusters can last forever. They seem to like Mobil 1. Mobil 1 has the right detergents or whatever ingredients to clean the lash adjusters and the passages that feed them to get rid of tapping. It takes a few thousand miles of Mobil 1 to get results. I don't know if the lash adjusters become addicted on it from that point.

There's a procedure to test lash adjusters. I'm not sure if it involves pulling the cam which is a PITA in the 603. If you're going through all that trouble you might as well replace all the lash adjusters ($300?). Check the new ones before installing because the defect rate is surprisingly high regardless of source.

Sixto
95 S420
87 300SDL

"Is there a common failure mode for either the fuel heater or thermostat? Is there a way to repair the thermostat? I also live in California, so I was wondering how important the fuel heater is in warmer climate?"

The failure in the fuel heater is usually corrosion from the hot coolant that runs thru it, allowing water to get into the fuel (nasty!) and is the same reason its recommended to change antifreeze every year or 18 months religiously in these engines.

Every time I change filters in my 87 300D it takes a lot of 30 second starter motor turns before it starts to fire off and then runs rough. While it's running rough, I hear tapping and it takes a while for them to go away. The taps in my case is "nailing" injectors after having disturbed the fuel system. Injectors seem to be very sensitive from my experience and may be what you are hearing!

Thanks for all of the good posts so far.

I have had the 1987 300TDT for about 1 year now, but I figure that I have only put maybe a 1000 miles on it since I bought it. I have been running Mobil 1 Truck and SUV (aka Delvac 1) for only about 650 miles or so. When I first got the 300TDT I noticed it made a metallic knocking sound that was not the usual diesel knock. More recently before I changed the fuel filter I noticed a tapping noise at idle that has been fairly consistent. After getting the 300TDT started today, I listened for the tapping noise and it seemed to be coming from under the valve cover. In order to rule out the injectors I think I will drive the vehicle for a few hundred more miles and see if things quiet down. I did a search on lifter replacement, and I think the procedure according to GSXR is to warm the engine up, pull the valve cover and then press on on the lifters one by one. If they squish down, then they are bad. I would rather not replace the lifters, so I will give it some time and see what happens.

As for the fuel heater/thermostat, I guess I will need to investigate the parts further. Since the whole fuel heater assembly is bypassed, I have no idea what is bad and what works. I was hoping any heat exchanger/thermostat failures would be something obvious since I don't feel like hooking it back up and taking a chance.

-Steve

I just replaced all my lifters. You'll likely have to test each lifter when the lobe on the cam is in the relaxed position for each lifter. They will all squish down at some point, but a bad one will have little resistance to squishing down. It's not difficult to remove the cam properly, and a magnet will extract lifters with ease! It took me a couple of hours from start to finish, I had fun doing it!

When the belt tensioner shock Heim ends wear out it can cause alarming sounds like rod knock. With the engine idling, press on the shock with a stick and see if that clears the noise.

Sixto
95 S420
87 300SDL