Engine noisy when hot and intermittent

[Gman67]

HI,
I have a 02 C220cdi.

The engine on startup makes a knocking almost clacking noise. if i increase revs to around 2500 rpm, the noise disappears and it sounds smooth as silk, even back at idle. Once the engine heats up the noise returns again (sometimes) at idle but disappears once driving.

The mechanics at work can't figure out what it is and mercedes dealer keeps changing a pulley tensioner.

other ideas have been turbo bearings and water pump bearing.

Otherwise car runs fine, no loss of power etc.

This has been ongoing for 2 years, car now has 80k miles on it. Trying to decide to keep or sell the car and if i could figure out the noise i would keep the car another year.

Any help greatly appreciated

thanks

 

[BlackC55]

Is it a combustion knock? or more mechanical?

 

[Gman67]

sounds mechanical,but difficult to say. no smoke or performance issues. I am going to try to record it....

My mechanic friend says it makes a noise that sounds like a small compressor ( if that helps)


Thanks

 

[BlackC55]

MMM not really.

Record it and let us hear it.

Can you pinpoint to an area it using a long screwdriver held against your ear

 

[Gman67]

I tried recording on my phone (with technical support from my 10 yr old!)

Of course it started up and was purring away quietly. I shut it off and restarted and the noise was there. Almost sounds like a tractor! rev up and goes away. when it runs and then gets noisy, there seems to be a click then it gets noisy, like something turns on in the engine?

I'll try the screwdriver trick and let you know what I hear.

thanks again.

BTW the recording on the phone sounds terrible, don't think it would help.

 

[BlackC55]

I have had a think and I know what it is.

The freewheeling pulley on the alternator is seized causing the belt to flap and become noisey. You need a special too to remove it. The pulley can be replaced. About £70

 

[BlackC55]

Any luck yet?

 

[recycled]

you must be a genius to deduce that fault just from that description

 

[BlackC55]

I have been called worse!