Strange engine noise when warm & poor compression results.
 

Greetings SmileWavy

My car has an odd noise when the engine is up to full operating temp. It's a high frequency (almost tinny) rattle/throb. It's almost like a vibrating heat sheild, although I've been all under the car and found no loose heatshields. It doesn't make this noise when cold, and when it does come on, it's not the usual lifter tick/clack. Doesn't sound like a bad rod bearing (knock knock) and it seams to dissapear when under load. If you leave the car for 30 mins or so then start up, it will be quiet, then after 5 minutes or so the noise returns.

Had the belts and rollers replaced last september. No water pump replacement to my knowledge.

Now, today I decided to do a compression test just out of curiosity. Numbers were

1. 145
2. 115 (ouch)
3. 140
4. 145

So bad compression on number 2. I'm starting to wonder if things are related. Could a possible broken valve spring cause this kind of noise? There was no oil on my plugs when I pulled them and theres never any excessive smoke from the exhaust to suggest it's burning oil or has bad rings.

The car doesn't lose oil. Oil pressure is in spec (5 bar cold 3 when driven for a while) Never overheats. Only thing I have noticed is the coolant sometimes needs topping up, but leaves no visible leaks on the floor, and no evidence of oil in the expansion tank.

Think the obvious next step for the compression results is a leak down test. But I was wondering if anyone here had experienced anything similar with this hot/cold noise?

Thanks in advance and sorry for the long winded post :cool:

possible roller or idle pulley at the front of the engine?

as for coolant, check at your head studs. also check the body of the turbo water pump.

Thanks Nynor.

Had the car jacked up today before I did the compression test and rooted around with a metal stethascope (long extension bar for a ratchet lol) and came to the conclusion the noise was loudest towards the front/belt cover area. Had the intension of pulling the covers after a multitude of other jobs but never got around to it.