About half the time I start my 1993 968, there's a loud screeching sound that is exactly like a belt is slipping. The screeching lasts for about 30 seconds, reaching a crescendo and cutting off like someone flips a switch. Both belts (power steering and alternator/air conditioning) are good and snug. It's not related to the A/C, because it will screech with the A/C off.

Today, I was driving the car while it was doing its 30-second screech, and the screech got really loud and cut off. When it cut off, I could feel a distinct increase in power from the engine, as though whatever was screeching was loading the engine. Since I've ruled out the A/C, I figure that there's a problem with either the alternator, power steering pump or water pump. (The water pump is driven off the back of the timing belt.) Everything seems to work okay while the car is screeching -- there are no dash warning lights for a weak alternator and the steering feels fine. I can run the A/C or not run it, and it doesn't affect the screeching.

I have a few ideas about how to troubleshoot this but wonder if someone out there has experienced the same thing and can point me toward the problem. Thanks!

Bob Kovacs

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It sounds a little like a problem I have. When the car have been parked for a long time, my cooler-motor sounds like a chicken on drugs :D
Maybe you should check the air intake cooler motor, im not sure what the english word for it is, but its just ind the front of the windscreen, and behind the torpedo wall.
I think you're talking about the heater motor, which is right at the base of the windshield. I had a screechy heater motor in my 1978 924, which I was able to disassemble and lubricate.

The problem in my car is definitely not the heater motor. A big clue is that a bit of power is restored to the engine when the screech "snaps off." It has to be something that would significantly drag the engine, such as a belt-powered accessory.

But thanks for the suggestion!

Bob Kovacs
It's probably the alternator belt because it's supposed to be pretty darn tight. IIRC, the P9201 belt tensioning special tool is supposed to read 2.5 for balance shaft belt, 4.0 for timing belt, and 9.0 for alternator belt!
I don't have the tool but the problem I have is more than just belt tightness. When the screech snaps off, there's a bump in power. The feeling is identical to what happens when the A/C switches off in a car with a smaller engine. Whatever is screeching is dragging the engine.

Thanks for the tightening specs, though!

Bob Kovacs
I hope you find an answer, Bob. I may be having the same problem. Not sure. I get a screeching when I first start the car in the morning. The voltage has now dropped to about 10 volts on the car meter. I was out driving with my wife last night, and the voltage started dropping the same time the Anti Lock Brake light came on. Shortly after that, the red and white exclamation light came on, but would dim out if I gunned the engine and come back on if I let it idle. This morning, I started the car to see how it was doing, and it ran OK with the voltage back up to about 13 to 14 volts. Then, it suddenly began producing lower voltage (around 10 or so volts) again. The engine also began to run a bit rough. I'm hoping that someone may have an idea as to what happened?


Monte Olsen
While very new to this car, I have also had this similar sound but mine fades away after a little driving.

i thought it was the A/C belt since it also cycled, but I did a rough check around and it seem to be more likely coming from the alternator, or in that area. It would fit if you are also seeing charging problems.

Now, exactly what with the alternator I am not sure, but could possibly be bearing wear and it could be intermittently seizing/dragging? Is alternator bearing failure comming with these? (Remember I'm new).
Hi Sprocket,
I'm a new guy to this, too, so I guess we're both in the same situation. I love this car, and I knew things would pop up. It's my first Porsche - something I've wanted for many many years. I did pop the hood and looked at the alternator, and it was spinning right along with the belt turning. Now, that doesn't indicate anything with the internals, so maybe that's where the problem is. If I discover something new, I'll post the information here. (I'm going to take it to the shop tomorrow.)

Thanks for replying.

Monte Olsen
Thanks for all the comments. I'm also leaning toward the alternator but didn't get a chance to test it this weekend. I'm hoping to check later this week to see if there are any charging issues. I thought the voltmeter was a little low (around 12V) when it screeched the other day, but I will put a more accurate voltmeter on it to get a better idea of what is going on.

Shouldn't a dash light come on if the alternator is not producing enough power?

Bob Kovacs
Interestingly, on my car that did happen but it was intermittent. When the light first came on, the ABS light also came on. Yesterday, no lights came on when the voltage fell.
do not trust the voltmeter in the dash. check with a more reliable one, as you stated. if the volts are low, warning bulb could be burnt out. have had to replace several bulbs in the 6-spd, as well as replacing main dashbulbs w/led's, replaced bulbs and odometer gear on tip.
my v/meter shows low on both 968's but is actually arnd 14 last time I checked.
a/c -alt. belt does have to be tight, I replaced mine recently due to a chunk ripped out of it and had to retighten twice (i do not have the 9201 tool, but luckily can compare to 2 other cars.) to stop squeal. if you do get the tool, remember that belt thickness does matter. I saw your article on your webpage, you seem to be pretty knowledgable, you prob. have a wkshop man., but as a reminder, do not forget to loosen the adj.rod mounting bolts before doing any adjustments, and tighten after!
Hi Kevin,

Thanks for your information. I'm going to do as you suggest and replace the bulbs in the dash myself. That all looks pretty straightforward (I hope. ), and run a voltmeter to see what is actually happening. I can say that there does seem to be a problem. When I took it to the mechanic this morning (I gotta start doing some of this work myself), when the engine revved, the volts dropped. When the engine didn't rev, the volts went up. I'm thinking it is a belt. I felt the belt, and it seemed tight, but I've made that mistake before. That tool might be the way to go.

This is a fantastic forum. It's reawakening my desire to do a lot of the work myself.
Thanks for the tips! I should be able to check the voltage today or tomorrow... I only hope it will do the screech so that I can tell if there's something about the voltage connected to the screech.

In my case, it is something besides a slipping belt. When the screeching noise stops (after 30 seconds or so), there is a distinct bump up in power. Something is bogging down the engine and causing a belt to slip. Once the bog goes away, so does the slipping belt and all is normal. I'm still leaning toward the alternator but it could be the power steering pump, for all I know.

Bob Kovacs


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