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Need a little help on this one guys! Been trying to figure this one for awhile now and have had no luck. About to pull my hair out!

1988 e28 528e 12/87 super eta auto 60k miles

Intermittent squeal/whine from engine bay only after car is driven 20+ mins and is at full running temp and stopped at idle or in park. She cranks up and runs fine and is normal on short trips.

Changed all belts multiple times, timing belt multiple times and have all oem in there now thinking this was the issue. Pulleys all seem correct with no play. Have taken AC belt off and used stethoscope on power steering and alternator. Noise origin seems to be around top front of head but not certain.

Also have replaced water pump, coolant temp, tested for vacuum leaks w/ smoke test, fan clutch, thermostat, run fuel injector cleaner, new spark plugs, spark plug wires, boots, cap, rotor, coil, power steering reservoir, coolant bottle and cap, trans mounts, gebo and adjusted valves… and more that I can’t think of.

Only thing I can think of that is left is the muffler has seen better days and probably has some rot inside?

No idea! Here is a video - might need to turn the volume up a bit for to be able to differentiate the squeal and whines.

https://streamable.com/2jbsh9

Let me know if I can provide any other information and thanks for the help!

That's a tough one. Have you tried getting it up to temp, removing the fan belt, and running it for a few moments? If the noise is gone, since you have replaced the water pump, that'd likely mean the alternator (even though you said you didn't think that was it).

It really is! Good suggestion, I haven’t tried removing it after it’s up to temp mainly because I haven’t been able to think of a time efficient way to approach while it’s still warm.

But also in the back of my head why would the alternator make any intermittent noises after getting to temp? Wouldn’t any of the parts in the alternator to fail generate a noise regardless of temp? The noise will go right away with even the slightest amount of throttle.

The alternator is a mechanical device, and components in that mechanical device change clearance as temperature changes, and any lubricant in bearings changes viscosity when temperature changes. Changing RPM changes the harmonics of the system.

Another excellent point. With not having any current issues with the alternator think I should try to change the voltage regulator and brushes first? Then move on to bearings and try to rebuild it or just bite the bullet and buy a Bosch and give the factory one back as a core?

Well, you need to see if it's making any noise before throwing parts at it.

Shawn D. wrote: Nov 18, 2024 5:49 PM Well, you need to see if it's making any noise before throwing parts at it.

^^^^ THIS ^^^^

1st 5er wrote: Nov 18, 2024 6:03 PM [quote="Shawn D." post_id=<a href="tel:1537118">1537118</a> time=<a href="tel:1731970173">1731970173</a> user_id=6419]
Well, you need to see if it's making any noise before throwing parts at it.

^^^^ THIS ^^^^
[/quote]

Well yeah… Per my original comment: A stethoscope was used and I advised “Noise origin seems to be around top front of head” and said that I did not think it was the alternator.

As I’m sure you are aware that belts and pulleys can effectively transmit sounds to different parts of an engine. So I was looking for something I might have missed. As everything has been checked in the front of the head that I can think of outside of the oil spray line or passages are blocked, but this seems far fetched.

The parts replaced is also general maintenance, just advising what has been replaced as a reference.