Klanking noise

[echo63]

My 83 944 (80k miles) has recently developed a strange klanking sound. I read this board y'day and initially thought that it could be bad CV joints, but the klanking only occurs when the engine is hot (freeway speeds) at varying speed, and sounds more like a rapid succession of the injector . In the morning when I start up the car it is silky smooth, until I have driven on the freeway for about 5 minutes or so, and then the klanking noise appears suddenly. Once the klanking starts, it stays on even when I'm on a stop light. Also, I noticed that the aux fan coming on after the engine shuts off sounded rough (but not the klanking sound). Can these be related? Any thoughts or suggestions? Thanks.

Ed

[Bob's944]

If i were to take a guess on that one, I would be thinking that something gets hot enuf to expand and start hitting a resistance, whick could be a valve sticking after thermal expansion of the 2 dissimilar metals... steel valve and aluminum head. How's your oil? A good gunk out treatment might be all you need.

[Richard Foy]

Does the clanking vary in pitch with the revs of the engine, or with the speed of your car, or none of the above?

[echo63]

The klanking does not vary in pitch, but the frequency does vary with speed. I checked the oil and there's enough, but it's time for an oil change anyway. I will try the gunk out as well.

Also, is it normal for the fan shroud to be making a rough noise when operating? My fan had always been loud, but it always sounded smooth, until now.

[PorscheG96]

You said that the frequency increases with speed...what speed? The speed of the car or the speed of the engine? In other words, is the klanking faster at 5k RPMs going 50 [2nd gear] or 2500 RPMs going 65 [5th gear]? I'm gonna guess that it's related to your fan housing, actually. After 5 minutes of driving is usually when the cooling fans begin operating, and since you say one is running rough it could be hitting part of the housing, or something else. Just need 'speed' clarified before I can guess more accurately. -Trevor

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'92 968 Amazon Green/Tan 6spd coupe -- Borla muffler, tint, turbo S front splitter -- parked, pinion bearing.
'86 944 Black/Black 5spd, 114k and running strong!

[echo63]

Frequency increases with higher RPM. I also suspect that something maybe hitting the fan housing, and will post the result of my further investigation. Thanks.

[ae1969]

uhmmm timing belt loose? tensioning roller loose?... check tension... increases with RPM.... (never realized how hard it is to guess from other peoples stories)

[41V]

you need to narrow it down more... your first 2 ideas were cv's, then fan... that's 2 totally opposite directions. Since it happens at idle, then easy...open the hood and listen carefully. At least narrow down front/back/left/right. You can buy a $5 mechanic's stethoscope (just like a doctor's) at a parts store and poke around for the source.
Outside shot the water pump is going down.