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Old 07-01-2008, 11:13 AM   #1
mrk45
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Default A hissing noise when shut off....

This is a strange one...new ZO6....less that 500 miles...I get home and put the car in the garage and turn it off. I hear a 'hissing' noise coming from the engine compartment....sounds like there was a leak in the cooling system. Opened the hood....no evidence of a leak anywhere and the coolant level is where it should be. Made an appointment with the dealer to take it in tomorrow to get it checked. It sounded like it was coming from the rear of the motor area...my initial thought is that it might be collected liquid from the air conditioning system running onto one of the exhaust pipes. The noise went away after about 30 seconds.

Any thoughts or prior experiences with this type of problem?

thanks,
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Old 07-01-2008, 11:27 AM   #2
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Mine did that and even though I didn't go to the dealer, it was decided it was the water from the AC dripping on the hot exhaust pipe, it still does it occasionally.
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Old 07-01-2008, 11:27 AM   #3
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Two things can make that sound. A/C refrigerent squeezing through the orifice tube as the system equalizes pressure. Or evap core condensation dripping on the exhaust. Both perfectly normal, don't sweat it.

I wouldn't take it to the dealer, last thing you want is those grease monkeys touching the car. Nothing is wrong. Run it with the HVAC system off then shut the car down, just to prove it's a norma A/C sound after shut off. All my cars do it. The high side runs at a real high pressure, when you shut the motor off, the pressure bleeds through the orifice tube to the low side until the pressure equalizes.

Last edited by Michrider; 07-01-2008 at 11:30 AM.
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Old 07-01-2008, 11:33 AM   #4
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Occasionally I get noises when I park my car.
The noise only occurs when the front of my car is lower than the back.
The noise sounds like liquid hitting a very hot surface which generates a hissing sound (vaporizing the water).

I think, in my case, it is the water from the air conditioner hitting the exhaust system.
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Old 07-01-2008, 11:48 AM   #5
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Quote:
Originally Posted by Michrider View Post
Two things can make that sound. A/C refrigerent squeezing through the orifice tube as the system equalizes pressure. Or evap core condensation dripping on the exhaust. Both perfectly normal, don't sweat it.

I wouldn't take it to the dealer, last thing you want is those grease monkeys touching the car. Nothing is wrong. Run it with the HVAC system off then shut the car down, just to prove it's a norma A/C sound after shut off. All my cars do it. The high side runs at a real high pressure, when you shut the motor off, the pressure bleeds through the orifice tube to the low side until the pressure equalizes.
+1. All of my cars do this as well. The cobra is especially loud. It almost sounds like a BOV.
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Old 07-01-2008, 12:23 PM   #6
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I agree with the others. Itís Ok you will be fine.
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Old 07-01-2008, 12:54 PM   #7
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Ditto here. I was told it is A/C condensation dripping on the exhaust. Like DaOtherOne said it only seems to happen when the car is listing one way ... supposedly the water runs along the frame in this case and then drips off onto the exhaust.

- Mark
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Old 07-01-2008, 02:14 PM   #8
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That's just the car taunting the Vipers. It does it while running too, you just can't hear it over the 427.
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Old 07-01-2008, 02:25 PM   #9
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Old 07-01-2008, 02:34 PM   #10
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I have had mine a week and it does it every time I park it in the garage.

It is hotter than hell

I am running the AC wide open

It is water on something hot

don't take to dealer
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Old 07-01-2008, 04:53 PM   #11
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It is AC condensation water hitting hot exhaust surfaces. I had it up on the lift changing the oil and saw it happening. Nothing to worry about..
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Old 07-01-2008, 10:06 PM   #12
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Quote:
Originally Posted by Michrider View Post
Two things can make that sound. A/C refrigerent squeezing through the orifice tube as the system equalizes pressure. Or evap core condensation dripping on the exhaust. Both perfectly normal, don't sweat it.

I wouldn't take it to the dealer, last thing you want is those grease monkeys touching the car. Nothing is wrong. Run it with the HVAC system off then shut the car down, just to prove it's a norma A/C sound after shut off. All my cars do it. The high side runs at a real high pressure, when you shut the motor off, the pressure bleeds through the orifice tube to the low side until the pressure equalizes.
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Old 07-01-2008, 10:23 PM   #13
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Quote:
Originally Posted by ByByBMW View Post
Mine did that and even though I didn't go to the dealer, it was decided it was the water from the AC dripping on the hot exhaust pipe, it still does it occasionally.


every time I use the A/C..........
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Old 07-02-2008, 12:08 AM   #14
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That's just the car taunting the Vipers. It does it while running too, you just can't hear it over the 427.
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Old 07-02-2008, 12:00 PM   #15
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Isn't he talking about bleed down from one or more of the combustion chambers as a result of turning off the motor? Valves closed, piston coming up on the compression stroke, engine shut off, air/fuel mix remaining and gradually exiting most probably seeping around the rings and into the crank case?
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Old 07-02-2008, 12:05 PM   #16
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Thanks for all of the replies. Took the car to my local dealer...whose Service Manager I know and trust...seems that y'all are correct in that the air conditioning system is what is causing the sound by the hi/lo sides equalizing. Not a problem...as noted by forum members.
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Old 07-02-2008, 12:11 PM   #17
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Does anyone else get the feeling that he doesn't trust us so much. ;-)
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Old 07-02-2008, 12:16 PM   #18
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I do trust the replies.....my only real concern is that I am leaving for a cross country trip next week and just wanted to be sure that there was nothing amiss with this new car and to get my concern on the dealer's records. Life is good!
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Old 07-02-2008, 01:50 PM   #19
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I know. Just messing with you.
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Old 07-02-2008, 01:50 PM
 
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