New whistling sound from engine?

[Hans57]

All,

I just finished with my valve adjustment/plug oil change etc. the other day. She runs great, but I hear an on again off again whistle kind of noise from the engine that is difficult to explain. I hear it about 30% of the time while driving, and it goes on and off. It sounds like - WEEEEEEEEEEEEEEEEEEEEEEEEweeeeeee... Then it stops completely. Kind of like a mini turbo or muffled Dremel tool spinning at 10,000 rpm. It will start up again with no particular RPM needed. The pitch does change with the RPM, and it will quit as soon as it starts. It almost sounds like a vacuum whistle or something, and it seems to be coming from the left side.

Any thoughts?

[Don Plumley]

No real ideas. Sounds pretty loud for a vacuum whistle. You can try spraying carb cleaner on the vacuum lines to check for change in idle. Is it possible you have an airbox and/or inlet leak?

[Hans57]

I will look at it carefully. I have a mechanics stethoscope that may help me isolate it. I'll be sure to let you know.

Thanks!

[BoxxerSix]

Very similar sound emulating from my buddies 965. Turned out to be the fan belt tension switch wheel/bearing.

[Newsboy]

Check The alternator belt sensor wheel. The bearing could be on it's way out.

[Hans57]

That is two votes for the sensor wheel. I sprayed a bit of LPS-1 on the bearing tonight, I will drive it tomorrow to see if it quiets it down at least temporarily. Thanks and I will keep you posted!

~jeff

[Hans57]

Whistling sound gone! These cars do not like to sit around.

Thanks, and looking forward to some Springtime top down motoring! Until then, we'll keep her running on the dry days in the Winter!

[BoxxerSix]

Originally Posted by Hans57

Whistling sound gone! These cars do not like to sit around.

Thanks, and looking forward to some Springtime top down motoring! Until then, we'll keep her running on the dry days in the Winter!

Figured it was that damn little bearing. If it ever comes back and you don't want to replace the entire switch send me a message and I'll dig around for the website where I bought just a single bearing in the correct size. It was a $10 bearing vs a $70 switch.

[Sonic dB]

Is this a 993? There is some whistling which can occur with the emissions controls for about the first minute after a cold start...but then it goes off and is not a factor... this is common in a 993.

[Hans57]

Thanks Adam. She is a garage queen, so it may be a while before it acts up again. I will definitely take you up on your offer if the need arises.
Sonic, this is a '91 964. Not sure about the 993 issues.

[BoxxerSix]

Originally Posted by Hans57

Thanks Adam. She is a garage queen, so it may be a while before it acts up again. I will definitely take you up on your offer if the need arises.
Sonic, this is a '91 964. Not sure about the 993 issues.

Not a problem. I'll dig around here and pull out the slip I have for that bearing just to give to you anyway. If not I can just measure it again and find the part number. I've got a few busted fan switches here. The actual switch rarely goes bad. Bearing usually gives up the ghost first.

For future reference, I believe the switches for the 964/965 and 993 are the same. I've replaced a few before, and I think the part number Porsche now uses is a 993-106-035-00-M260 number anyway. IIRC there is a slight difference between a 3.3 965 and a 964/3.6T/993 switch body and how it bolts to the bracket on the fan shroud, but I think they still fit. I had to swap a newer switch into a 91 Turbo before and I think I had to finagle it a bit to fit thew bracket properly. I know the NOS 3.3L switch and 3.6/993 switch have different wheel "arms" but still function the same.


-Adam

[Hans57]

Thanks a million!

Happy New Year to you and yours.......