Hey guys, this started several weeks ago when I started my '95 E320 wagon: very brief squeal from the engine bay. It doesn't do it every time it is started, however, it is becoming more common an issue and is lasting a bit longer - we're talking maybe 2-3 seconds. As acceleration is increased so is the squeal, conversely, it stops when letting off the go-pedal.

Battery tested at 12.x volts not running. With engine running (nothing electrical engaged other than the auto climate control in AC mode) it shows 13.68v. Thinking I should be seeing something north of 14 - 14.5v...


Voltage regulator maybe? Testing procedure?


Thanks for helping diagnose


Dale

__________________
Dale

Time to change your drive belts.

Along with a belt change as suggested you may want to adjust or simply replace the belt tensioner while you are at it.

A cheap but effective tool to have in your toolbox is a mechanics stethoscope. This can help you sort out specific noises while the car is running. Check all accessories for undue noises, such as alternator, water pump, power steering pump, air pump and AC compressor. Any one oc these could be contributing to the noise and a stethoscope will help pin point the problem

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)

Slippage rarely happens with a serpentine belt, even if it's worn. Reading 13.68 volts at idle isn't necessarily a problem.

You may have worn alternator bearings, a weak belt tensioner, or a bad idler pulley. Where I would start is by removing the belt. While it's off, check the idler wheel for trueness and make sure the bearing turns smoothly without wobbling. Idler pulleys tend to wear into a cone shape, so inspect for a tapered rolling surface. Also make sure the tensioner has good tension. Spin the alternator pulley by hand, and feel for roughness. Finally, check the a/c compressor and power steering pulleys for smooth operation, as the belt ties all of this together. If you can't find any other problem, install a new belt.

Is the 13.68 reading taken with a stone cold engine or one that's warmed up?

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

It was warmed up. Had been out for a while and did it when arriving home and in the garage.


Dale

__________________
Dale

It has the 'squeal' of a bearing failure...


Dale

__________________
Dale

I failed to mention in the OP, that the car had just been in for service at my indy shop. I trust my indy a lot, but I'm not sure he id'd this one. He said he didn't/couldn't get it to 'squeal' so he checked serpentine, the tensioner, and adjusted it, AND...


Said that what I was hearing was the air pump making a racket and he went ahead and disconnected it to render it useless. Well, it wasn't the air pump I was hearing because IT did not make a squealing sound! (Reminder to self: call indy shop soon to inform them of a misdiagnosed problem.)


Unfortunately I don't have time until later this week to delve into it but wanted to get some ideas as to the direction to start. Thanks for the input it does help me out!


Dale

__________________
Dale

Very likely the tensioner. Really lousy design. While you have the entire front of the car apart, do the water pump, idler pulley above the smog pump (a new one comes on the tensioner), radiator and other coolant hoses, and a new belt. Wonderful way to blow $700.

All this was done by me three years ago so I'm a bit reluctant to assume all that is ready to be replaced. I used all OEM parts and some MB if I'm remembering correctly.

Dale

__________________
Dale

Get one of these and being extremely careful with moving parts listen to anything that contacts the belt.

__________________
07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126

This.

Get one of these and being extremely careful with moving parts listen to anything that contacts the belt.

__________________
07 E350 4Matic wagon, 06 S430 4Matic, 99 SLK 230
retired W210 (x3), W124, W126

"All this was done by me three years ago so I'm a bit reluctant to assume all that is ready to be replaced. I used all OEM parts and some MB if I'm remembering correctly."

All this was done by me four weeks ago and the new alternator died, dead as a hammer, no output. That's why I'm getting rid of mine. Tiredof working on it once a month. Take the belt loose and see if you can spin each individual component to see if you have a bearing going bad. If not, it's a bad belt or a bad tensioner.

Car or alternator? My assumption is you are referring to the car. The reason is because I'm beginning to get these thoughts popping in and out of my head. Whenever the daily driver is nearly 25 years old with 187,xxx miles on the clock - STUFF happens, and seems more often nowadays. Then I start trying to guess what I would replace it with and since car payments are not an option, I'll likely keep this one on the road.

Fairly certain my alternator is original so if it's bitin' the big one, I got my money's worth from it. Good luck!

Dale

__________________
Dale

Car. Sick of working on it once a month, at least. I just bought a 2012 Ford Flex Titanium, so the 300TE is available for $3000 firm. I have spent over TWICE that on it in the past year in parts alone. I have had all the Mercedes prestige I can stand for one lifetime.