dull knocking noise at hot idle?
 

is a dull knocking noise at hot idle normal? oil level is on the money and was changed recently. the noise seems to be intermittant, it wont doesnt happen when the car is cold. is this the air pump possibly?should i start saving for a rebuild?
pete

Buy a stethoscope and trace it.

I have seen so many different things cause this. Worn bearings, wrist pins, piston slap, even valve train noise. I wouldn't run just yet but I would start listening and looking at the oil to see if you have bearing wear, loss of oil pressure and so on. You will find that a certain amount of slap is common with these cars and more noticeable at temps because the oil thins out and isn't as much as a buffer.

Piston slap can wear rings faster but not life or death. The RUF short skirt pistons slap so bad you think you lost a bearing! But considered normal.

Without hearing the motor I can only offer suggestions.

can i notice bearing wear by smearing the dipstick on a white sheet of paper? when should i start looking to rebuild? the car runs fantastic. the carrera tensioners have not been done ,would this be my noise?

What is your idle speed. FWIW, my 87 930 had the same symptoms. When cold, everything was great, however, when it got hot, it had a dull knock as you described. I took it to my mechanic and he told me that if the idle is below spec on some turbos, the intermediate shaft will sometimes make noise. In fact, my idle when hot was around 750 rpm. As he raised to idle up to around 900 or 950 rpm, the sound completely went away. No more issues.

Mike

Not really. You would want to send it in and have an analysis done then do it often to look to see if any levels are going up.

Chain tensioners can also make this noise. This is why it is important to determine where the noise is coming from first.

Get a stethoscope. I was amazed how good it was at locating noise. I only got a cheap one.