1987 300TDT cranks but doesn't start and other fuel system questions - PeachParts Mercedes-Benz Forum

swogee · #1 05-31-2005, 12:34 AM

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?

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