Hi! Im driving a '76 123 200 diesel Mercedes. Despite its age, the car has been performing well, judging from the performance standards set in the manual. Its a beast of burden. According to the manual, our driving conditions are characterized as 'severe' (stop-and-go traffic, tropical temperatures). I drive it everyday in these conditions!

The problem is, after reaching operating temperatures (more or less 80C), the car will not start if you turn off the engine. That is, there is no problem if you start it when the engine is cold, but if you try to start it after driving for about 30minutes, the engine will just turn slower than usual and will not start. The only recourse is to wait for about 30minutes for the engine to cool down. Or you can push-start it. Either way, its been really irritating.

So, trying to solve that problem, we 'overhauled' the engine (Yep, overhauled it according to specs!). We replaced all bearings and gaskets, but not the piston rings, because they're quite alright and are expensive. We installed a stronger battery, replaced all fuel filters, had a change oil and filter. However, despite these efforts, the same problem arose, though this time, it seems that the engine cranks more easily.

What could be causing this? My car still uses the old type of injection pump which doesn't use vacuum to turn the engine on or off so it aint probably vacuum related (it uses the cable-type to push or pull the 'lever').

I haven't had the injection pump calibrated, so that might be it, though I do not know what might cause it to fail.

Could it be the starter motor? Why?

I need help. I usually do the repairs myself, if I have the tools for it. Im on the verge of a nervous breakdown! I love this car and I am not about to sell it or give up the ghost! Thanks!