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Duncan

I hear a very faint hissing noise after my engine shuts down, like very soft from the back of the engine... It lasts a couple of minutes.

Any idea what this could be?

Cheers,
Duncan
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1983 NA Alpineweiss since 2001
Peugeot 205 Generation

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Vac leak?

Coolant leak? Perhaps a pinhole leak in one of the heater core hoses, or head gasket at back of head?
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erstwhile owner of just about every 924 variant ever made

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Did you check for snakes?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Duncan · Posted: Thu Mar 31, 2011 7:07 am Post subject:

Yes I did. No snakes I am aware off.
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1983 NA Alpineweiss since 2001
Peugeot 205 Generation

!tom · Posted: Thu Mar 31, 2011 7:13 am Post subject:

Brake booster (and associated plumbing)?
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78 924 NA
5-lug

Duncan · Posted: Thu Mar 31, 2011 7:17 am Post subject:

Thanks for all responses,

I would like to stress it occurs after shutdown.
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1983 NA Alpineweiss since 2001
Peugeot 205 Generation

Ozzie · Posted: Thu Mar 31, 2011 8:06 am Post subject:

only fuel and coolant stay pressured after shutdown
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Lovecake · Joined: 04 Oct 2006 Posts: 15 Location: Brisbane, Australia

I had this hissing problem, and several others (very loud tappety noise at start up, deep warbling/rattly noise at around 2k rpm). Turns out the nuts holding the exhaust manifold to the head had come loose (the front one had fallen off

). Anyway, replaced/retightened them all and these noises, including the hiss, disappeared. Might be worth a try.
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'68 VW bug
blue 1979 924 N/A (wounded/parts car)
red 1982 924 N/A

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

mikebola · Joined: 07 Sep 2009 Posts: 361 Location: Parkside, PA

Duncan · Posted: Thu Mar 31, 2011 4:17 pm Post subject:

Can you explain to me how the brake booster can hiss?
The moment the engine stops the vacuum drops, I would think.
Or am I missing something?

I never focused attention on the brake booster, but will do that next time.

Cheers,
Duncan
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1983 NA Alpineweiss since 2001
Peugeot 205 Generation

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

There should be a check valve in the line to the brake booster so that it maintains vacuum regardless of what's going on with the engine...otherwise, you would lose brake assist when you were at WOT...
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erstwhile owner of just about every 924 variant ever made

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Yep, check valve. I can make my booster line hiss by wiggling the hose in the rubber fitting at the booster.

Dan, I chuckled a bit thinking of all the times I have been on the brakes at WOT!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Joes924Racer · Posted: Fri Apr 01, 2011 2:29 am Post subject:

Coolant hoses going to the heat exchanger or one of the other coolant hose connections along the line there in the back..
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.