Car: 1989 Volvo 740 Turbo with M46 manual gearbox.

Only on really cold days, when I start the car there will be a momentary whine as the engine gets up from starting speed to idle. Then it would go away. Now its even colder and at around 2k to 3k rpm there will be a loud whine too. It goes away after the engine has heated up to about 1/3 running temperature. It sounds close like it is near the firewall, but I haven't checked under the hood for the noise since it goes away before I intend to check it. It's not in the transmission since I have put in the clutch and gotten the noise with just the engine going at 2k to 3k rpm. It sounds like a bearing going bad. I know that there is a pilot bearing in the clutch, but I don't know what the does. I only know of a throw-out bearing. But I don't understand why it would make noise independent of the transmission speed. The really weird thing is that it goes away once it heats up. On a day above freezing, the car doesn't even whine on start up. So any thoughts?

 

Well, if you get the noise when the tranny isn't in the picture pretty much points to something on the engine. What you describe commonly is an accessory bearing. For me, most commonly the alternator. Oh...the pilot bearing mounts inside the rear of the crank shaft. The nose of the transmission's input shaft rides in it. I have had them make noise but rarely.

 

I put a new alternator on last year. My old one's bearings were really noisy. I could be crappy quality "advance auto" bearing special. I'll do some checking and make sure it's not the steering pump too.

If I understand the pilot bearing right, it should only make noise when the clutch is disengaged if it is bad. When the clutch is engaged, the bearing spins with the transmission input and the crank shaft and bearing is effectively doing nothing. If that's true, that rules that out.

Thanks.

 

But...the crank is always turning when the motor is running. The input shaft nose is always in the center of the bearing. They can make noise regardless but...it is seldom the case. A/C clutch?