I just purchased this 1987 300TDT and it is my first diesel car (I do own a diesel tractor). It has 96,000 miles on it. At start up it runs rough, as if it is only running on 4 cylinders and it smokes alot. After about 1 minute it runs perfect.It runs better if I cycle the glow plugs twice before starting it. I thought I may have a couple of bad glow plugs but in the complete set of reciepts I got with the car, I noticed all the glow plugs were replaced two years ago....Any ideas?

It is so easy to check glow plugs. The shay tree way, and it works just fine, take a 12V headlight and make a terminal to put the headlight between the glow plug and the headlight. Turne the key on, and if the light lights up good, you have a good glow plug. If the light is dim or doesn't light at all, the glow plug is bad. The best way is buying a test light that tests ground. But it sounds more like you need to adjust the valves. A Merecedes diesel will smoke really bad when the valves are tight, and start bad too. That no compression thing play a kay roll.

Two years is plenty long enough for one plug to go bad, it depends on the use not the time. If the car was started many times a day and driven in cold climates where the GPs cycle extra long then you can certainly burn them up in 2 years, plus the fact that one may just have been defectived from the beginning. You symptom is classic GP failure, start there and see if they are all good...if so you can start fooling with valve adjustments.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Thanks for the help! I've learned alot....

To my knowledge the 603 engine does not have adjustable valves, they are hydraulic. If there is a problem with tight valves then you may need to perform a valve job but that is another story............ Start with the GP's as suggested.

If you need to look further than the GP's there are other items which contribute to cold start problems. You may be required to do some inspecting and adjusting...............no biggie!

there are quite a few posts on the forum regarding this starting issue with the 603 engine.i recommend a search.beleive me yu are not alone

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon

Yeah, you are right. I guess I overlooked the year.

No foul