I was idling my 300d in the garage just after getting home on a short drive. It ran great and I had good oil pressure, etc.

I was adding ATF to it because it was low, and after I got the dipstick/lid back on, the rpms sort of hiccupped and I developed this rapping from the engine. Sounds like a bad nailing, etc, and it was accompanied by some whitish/greyish smoke at idle, which has never happened before. I took the oil cap off, and the blowby is no worse than before, but now I Have this knock.

It is not exactly consistent, as the cadence changes and sometimes instead of a steady rap-rap-rap-rap, I get a rap- -rap- -rap.....

Is my engine shot, or is there something else I can check?

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)

Begin isloating the noise:
---use stethoscope in various regions of the engine
--- loosen injector line nuts at the injector one-by-one


If you begin to suspect that it is the lower end (crankshaft bearings / rod bearings):

---pull the crankcase oil dipstick and observe the oil in a very strong light source, you may be able to see metal flakes in the oil

---drain oil and pull the lower oil pan off and inspect for metal shavings


If you have been burning unrecommended fuels, you may have destroyed a prechamber. The material is now bouncing around between the piston crown and cylinder head. Or enlodged in the piston crown and repeatedly banging against the cylinder head.

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Well, I started it again to begin the diagnosis process. I revved it up to see if it went away at higher RPMS, and it just stopped. No more smoke at idle, etc.

Could one of the injectors have had some crud in it that got blown out?

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)

Good and reasonable guess that perhaps one injector was stuck open. The additional sudden smoke indicated it was not a rod bearing at least anyways.

My experience with cars has been overwhelmingly with gasoline engines....thus when I start to hear sounds like that, I sort of freak out. I've had rod bearings go before on other motors, and I know this didn't sound like that, plus there was no loss of oil pressure.

It ran great on the way to work today...no smoking....now all I have to do is stop that transmission leak.

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1983 300D - 314,640 miles (not all by me) - Daily Driver --Sold--
1983 300d - 215,000 miles (approximately)