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Old 11-22-2008, 01:07 PM
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Loud Squeal -- Alternator Upgrade Question

A few days ago my car started making a wild sounding squeal, really loud. It lasts for just a few minutes after turning the car on, then goes away, though now it seems to last even longer than a few minutes. And it's only when pressing the pedal and going about 10-25 mph, so I can't open the hood and listen. It sounds like it's directly in front of me, towards the front or middle of the engine. I sprayed some belt dressing on there and it hasn't helped. The belts are relatively new and the tension feels fine.

This started right around when it got cold and right when i did the violet wire mod on the glow plugs. I can't imagine how it's related though. Could it be something other than the belts? The other thing I've noticed recently is that the battery light stays on after starting the car. It goes off when I rev the engine. Could this be something other than a belt?
1980 300D, 128K

Last edited by kenstfelix; 11-25-2008 at 05:47 PM. Reason: title not specific enough
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Old 11-22-2008, 02:00 PM
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Rollin' on 16s
Join Date: Dec 2005
Location: Vancouver WA
Posts: 6,528
It sounds like a belt, probably the alternator belt since it is only after starting when the battery is being charged after the starting load. Mine is doing the same thing, belt tension seems OK on mine too.
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine
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Old 11-22-2008, 10:23 PM
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Does this mean the battery's getting low? Or I'm putting too much strain on the alternator?
1980 300D, 128K
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Old 11-22-2008, 10:48 PM
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Posts: 897
Small exhaust manifold leaks can also manifest with a squeal which goes away as the manifold heats up and changes shape. Check all manifold bolts for tightness.

Chris W.
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Old 11-22-2008, 11:34 PM
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Join Date: Jun 2008
Posts: 343
About 70% of the time it is a loose or bad belt. 25% of the time it is an accessory bearing (usually idler pulley). The other 5% is, well, other.

A belt you can feel with your finger. Accessories you can often tell by raising the hood but sometimes it takes a rubber hose to the ear. Try the easy checks first.
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Old 11-25-2008, 03:40 PM
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Join Date: Mar 2008
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I reconnected the purple wire to the glow plug relay and it stopped the squeal. I guess my alternator just couldn't handle it. Unfortunately, now my car is starting rough again. Is there anyway to make this work? I don't want to stress my alternator and destroy it. Would I have to get a high output alternator or something?
1980 300D, 128K
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