Tonight on my way home from a very short drive to the grocery store, my 350SD started making a very loud squealing sound. It got faster/higher/louder with acceleration. My A/C has been squealing some for the last week or two - could it have something to do with that? The squealing tonight happened without the A/C on, though. It didn't seem to affect the power and nothing was overheating, no gauges going crazy or anything, but it is present at all times when the engine is running.

I did notice that the engine ran a little bit longer than usual when I shut it off, and then did the same thing again when I restarted it in the garage once I got it home. I didn't notice any smoke at all, though.

Any thoughts on what this could be? I just had a lot of work including new aux fans, fan clutch, t-stat - could it be related?

Sounds like the serpentine belt is slipping...thats usually what causes slipping....maybe the belt tensioner is having issues?

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Did you mean "that's usually what causes squealing" or did you mean slipping?

The serpentine belt was just replaced among the other work that was done - that could be it.

Yes. I meant squealing...sorry. I'm a little bit tired...

It is most likely the belt....either the belt itself or the tensioner....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Okay, now here's my question:

Is it unsafe to drive 10 miles to my mechanic with this squealing? Might I really mess something up, or should I have it towed?

Look carefully at all accessories while the engine is running. Make sure they are all turning.

Shut the engine off and feel all the pulleys looking for signs of excessive heat.

If you find any issues with excessive heat or one of them not turning whatsoever, have the vehicle towed.

If all pulleys are cool to the touch (do this test on startup), then you're probably safe to drive it.

Thanks Brian - I'll check it out before I drive it; I was planning to take it to my mechanic today for a tweak on my WVO system anyway, but not for this!

In particular check the A/C Compressor Pulley. If the Clutch has seized then that would cause the belt to squeal like crazy. You mentioned you had been having some squealing with the A/C on.

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Yes, it had been squealing some with the A/C on - so what is the prognosis if the clutch has seized in the A/C compressor? If it means I need a new A/C compressor, then it's a good thing it has started to cool down here in Vegas, 'cause I probably won't be getting a new one until next spring!

whens the last time the belts were changed? could be a belt loosing its grip, as they tend to do with age, and snap eventually... not that hard to put a new belt on

The serpentine belt was JUST replaced about 2 weeks ago when I had a bunch of work done inc. aux fans, fan clutch, t-stat, etc...

do what brian said

I just spoke with my mechanic - the problem is a defective tensioner; $96 for the part plus labor. I'm glad it's not something more problematic (or expensive!)

Thats a lot if he just replaced the shock.

I was going to say shoot it with water and see if the squealing went away.

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If the clutch fan axis isn't parallel to the crankshaft axis, there's considerable risk of the fan cutting into the radiator even driving 10 miles.

Sixto
93 300SD