Recently entered the W123 diesel world by buying a cheap 1981 240D 4 speed on CL. Relatively new to these OM616s, would greatly appreciate any wisdom you Mercedes experts have to offer.


The car's odometer shows 109k miles, but has been broken for some time. Previous owner estimates closer to 200k. It was cheap due to the engine needing a valve adjustment, according to the PO. The car was in decent shape otherwise, not much oil leakage, decent interior. I test drove it briefly and clearly could hear a tapping coming from the engine, which I assumed to be the valve train. It was directly proportional to RPM. The more load I put on the engine or higher RPM the louder and faster the tapping got. It almost sounded like really loud injectors.



Decided to buy the car and adjust the valves and pray that's the sole reason for the tapping. I live about 3 miles from the buy site and after some thinking decided to drive it home on surface roads rather than opt for a tow.


Drove it back and it seemed to be handling it fine until about 1000 ft from my house. Had to stop at a stop sign and felt the engine struggling to idle, wanting to die. I kept it going by breezing through the stop and putting the pedal to the floor, but there was one more stop sign before my driveway, and had to stop here because of a school bus dropping kids off. When I slowed this second time the engine stalled. No warning lights came on during the drive and oil pressure was fine. No overheating either. Tried to restart and the engine barely cranked, sounded like a dead battery. Decided to just push it home and figure it out from there.


Got it home and decided to jump it and see if i could it started again (maybe the battery really was dead, dying alternator I didn't know about?). Got it started, but quickly shut it off as the original tapping sound had now morphed into a much louder and more menacing tapping/grinding sound.


Worried I had caused some other internal engine damage by running the car without adjusting the valves, I did some inspecting. First I did the valve adjustment, which turns out did need to be done. This also revealed that at least the engine wasn't seized, crankshaft turned fine. I also dropped the oil pan to look for metal shavings thinking maybe something in there got shredded somehow. Oil was pretty old but no shavings found. Pulled the glow plugs thinking that may give some clue about what's going on (not sure if this is as effective a diagnostic procedure as it is in gas engines). There was a small ring of black soot on each one about halfway up the pencil.


Wanting to avoid starting it again until I know exactly what's going on for fear of damaging the engine even more. I'm doubtful that it was only the valves that caused the stalling and subsequent tapping/grinding. Maybe I exacerbated some pre-existing problem or caused a whole new one. I know there are about a thousand things that could cause a stall, but before going down that rabbit hole of checking fuel, ignition, and compression, I'm hoping this can be narrowed down a bit by someone who knows much more about these cars than me.



Any tips on things I can look for that might give me a clue to what happened? Would love to get this baby on the road soon. Any advice would be greatly appreciated.



Thanks!