[c4koh]

All,

Since yesterday, my 92 ZR1 has developed what I can only describe as a very resonant "parping" noise above 3500rpm, and only with the secondaries (full power) on. Power seems somewhat reduced, but the car is certainly quicker with the secondaries on than with the power key off. The sound sorts of bellows throughout the entire car, and sounds like it's not breathing / exhausting right...

Background -
The engine ran very hot yesterday (261) as for some reasons the cooling fans were not coming on and I did not notice, though it was only a short journey. I got home, due to hearing the "parping noise" and then tried to listen to the engine when still, but the noise isn't discernable at a stop. It was while doing this check that I noticed the engine was hot, but I can't be sure if it had been hot earlier or just at that time.

The cooling fans seemed to come on no problem today, I did some wiggling of the relays to test them (shorting the A-B pins on the ALDL) and maybe that fixed a loose connection. Don't know, but they're on now and engine was fine heat-wise.

Other than running hot, there is a slight vacuum leak hiss (has been for a while, was not apparently affecting anything) from under the plenum.

That's all I can describe. I'm going to comb through the forums to understand more, but any quick hints as to what I could / should check? Could I have blown a head gasket (would it give these symptoms) due to the heat? Will check oil for chocolate milk froth, and coolant for oil shortly...

Any help appreciated. Will write back to the thread as and when it's resolved (these forums are great when you read a problem and the OP posts the resolution :-) )

Thanks all.

Steve

- Edited to add:
Car is stock.
No service engine light on.