I'll usually go a few days without driving my 240D, and when I do end up starting it up, the engine will knock for about 5, 10 minutes. Once it's on the road, though, it's fine. Is it normal for these old diesel engines to do this when they're cold/not warmed up?

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- 1979 W123 240D 4-speed, 390k miles

I'm not quite sure what you mean - knocking can mean so many different things.

If you are really concerned about it I recommend that you record the sound (video camera) and post it up somewhere so we can hear what you are talking about.

Instinctively I'd guess that the non return valve in the filter housing is letting the oil flow back down into the sump and so there's a fair amount of racket going on until the oil has been pulled through the engine again - however - it could also be injector knock - it could also be little end knock it could also be vacuum pump knock...

...you see what I'm saying? It could be lots of things! The best thing to do would be to get an experienced mechanic (who knows about OM617s / OM616s / OM615s) to listen to it. The next best thing => post up a video with sound.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

How many miles on the car? Since the knock goes away after five to ten minutes it may not be anything serious. To get yourself into a comfort zone have someone with a lot of experince listen to the engine and identify the noise if possible. Or at least try to identify the cylinder by loosening one injector line at a time. If you identify the cylinder try swapping injectors and see if the noise moves .

I am certainly not recommending it but if I was satified it was not a rod bearing I might consider giving the engine an italian tuneup.