Little Birds Chirping Under the Hood - PeachParts Mercedes-Benz Forum

bmeares · #1 02-19-2008, 01:19 PM

I recently was told by my shop to replace the fan clutch in my '86 190d 2.5 5spd. The a/c compressor is shot and was making a little noise, but not too badly. I replaced the fan clutch and while I was in there replaced the vacuum pump.

Shortly after replacing the fan clutch, I noticed a little squeal that happened any time that my foot was on the gas, but not at idle. This only occured for 15-20 minutes and then stopped.

Now, my car is making the "Birds Chirping Under the Hood" squeal, but only while the engine is slowing down to idle speed (not while driving) and only once the car is good and warmed up. It isn't present when I start up in the morning, but when I take my foot off the gas after 30 minutes on the highway, it starts up, and diminishes as the engine slows to idle speed, but is still audible at idle. If I idle for a little bit it will all but go away.

What could this be. Could a very slight pinch of the top of the fan clutch pulley (had some trouble getting the stripped bolt out when removing the fan clutch and ended up using vice grips) be making the water pump bearing squeal when the car gets warmed up? Could it be the a/c compressor bearing going out, though this wouldn't seem to jive with the quiet when cold, squealing when hot, but only at idle speed symptoms? Or something to do with the new vacuum pump?

Anybody got any ideas of where to look first?

THANKS!!

AdvisorGuy · #2 02-19-2008, 01:37 PM

Belt ? Belt tensioner ?

Grdenko · #3 02-19-2008, 01:52 PM

could have gotten some oil or grease on the belt while you were working in there. the noise might go away if thats the case. how long has it been going on?

bmeares · #4 02-19-2008, 03:22 PM

It has been a good 100 miles since I did the work, so probably not oil or coolant on the belt. I did a little road test over my lunch break and found that my previous description of when the noise occurs wasn't totally accurate.

The noise starts when the engine reaches full operating temp. right above 80 degrees C, and not before. It starts loudly when I shift gears and let in the clutch, right when the engine hits idle speed after coming down in rpm. It then lessens after being at idle speed for a second. It doesn't happen when the engine is warming up or at anything above idle rpm.

Hmmmm??

- Could it be the water pump going out on me?

SW · #5 02-20-2008, 12:54 PM

Is it in anyway related to when you push the clutch in/out?

JimFreeh · #6 02-20-2008, 12:59 PM

Quote:

Originally Posted by AdvisorGuy

Belt ? Belt tensioner ?

Sounds like belt tension. As you accerate/decellerate, the belt slips on the crank pulley, creating the chirp.

Jim

WINGAS · #7 02-20-2008, 01:09 PM

Tighten the belt is all.

bmeares · #8 02-20-2008, 03:14 PM

Thanks - there's no doubt that the belt could be displaying the symptom (chirping) - my questions is the cause of the slipping. It only happens at full operating temperature - Is there any logical way that the water pump is causing slipping when at temperature and swapping in a new one will fix it?

It would sound like merely a tension issue, but if that was the case, wouldn't the chirping occur regardless of engine temp?

bmeares · #9 02-20-2008, 03:41 PM

Quote:

Originally Posted by WINGAS

Tighten the belt is all.

I did notice that the shock is mushy - to tighten this sucker up, do I need a new shock, spring and tensioner tool - all had on ebay for about $100?

JimFreeh · #10 02-20-2008, 07:47 PM

Quote:

Originally Posted by bmeares

Thanks - there's no doubt that the belt could be displaying the symptom (chirping) - my questions is the cause of the slipping. It only happens at full operating temperature - Is there any logical way that the water pump is causing slipping when at temperature and swapping in a new one will fix it?

It would sound like merely a tension issue, but if that was the case, wouldn't the chirping occur regardless of engine temp?

Materials expand with heat.

Jim