I have a BMW 320i (M50 with Vanos) from 1993 with 150.000 km on the meter, and I have the recent time as temperatures are dropping to below 0 C degrees in Denmark observed that when I start the engine from completely COLD condition, then SOMETIMES the engine starts with a radling noise (tak tak tak), which then quickly disapears after 1-2 seconds. It is not everytime that the sounds appears, and that puzzles me a bit.
I was thinking about the following sources to the problem:
1) The hydraulic camshaft chain tensioner
2) One or more of the hydraulic valve openers (even though I think the noise is too loud to come from a small valve and I dont hear any ticking from the valves at normal hot engine operation....but maybe)
3) Something in the clutch (it feels a little worn and you have to lift the clutch pretty high to make the car drive)
Both 1) and 2) are related to the oil viscosity at low teperatures, but what do you think? Am I completely wrong or does anyone else have other ideas?
As a background information I can mention, that earlier I have had problems with another radling noise originating from the lower part of the engine, but ONLY when the enigine was warm and had been driving with a lot of use of the clutch and ONLY at idle speed. But after I took it to a workshop and they used some engine oil system cleaning chemical and then added some new oil (0W30 full synthetic), the noise completely disapeared and have not returned. I then made the conclusion that the sound must have come from a dirty hydraulic camshaft chain tensioner not operating properly and therefore not tensioning the camshaft properly at idle speed. Becuase of the earlier problems with the camshaft tensioner, I am suspecting that it could be the source of the problem again.....what do you think???
Hope you can help me with some input.