When turn engine off i can hear a hissing sound coming from under bonnet the end that meets the windscreen
Sound is completely normal on all Audi's.
Your A8 uses an Orifice tube to regulate the pressure between the two halves of your air conditioning system. A hissing sound is normal after a shut down as the system equalises. Usually lasts about a minute and is more noticeable on warmer days.
Location on an A8 is on the very right hand side of the bonnet just under the windscreen - that's where the hissing will be coming from.
SOURCE: '99 Chevy Silverado hissing sound under the hood.
You may have a disconnected or broken vacuum line. With the engine running, open the hood and try to locate the noise.
SOURCE: renault clio bonnet wont open
Get a second person to pull bonnet catch and you push up and down on the bonnet whilst catch is being pulled. 1, cable possibly stretched, 2, look at bonnet catch under the coloum to see if wire is attached, 3, try and lie under car and look up the back of the bulkhead to see the catch and release it manually. Hope that helps.
SOURCE: hi i have a audi tt 3.2 dsg
The problem with your car is that the oil drains back down into the oil pan after sitting. I have this problem at my work where we change oil. After each oil change there is no oil in the motor, it is all in the pan so every single car knocks something fierce when we start it up after adding new oil because it takes awhile to get to where it needs to be.
In your case, probably a seal in the oil pump or the pump itself. Once or twice this is no problem, but if it does it every day you are severely wearing out your engine components without oil flow.
SOURCE: audi a4 mixing water and oil together hissing,grey/brown foam
That is not true oil and water being mixed can come from many different places. Such as a bad radiator which would cause transmission oil to mix with the water also alot of audi's have a water cooled oil cooler which are a very common cause of oil being mixed with with water. These type of oil coolers are located under you oil filter. They have water lines hooked to them which cools the oil and when they go bad the water and oil will mix. So dont be convinced that its your head gaskets it could be but not as likely. You can pressure test your oil cooler to see if this is the problem just romove it an plug one off the inlet or with rubber plug which can be purchased at you local hardware store (I found mine at ace hardware in there specialty drawers where they have all there bolts) then attach a air hose to the other outlet pressureize the system and place it in a bucket of water. this should tell you if the oil cooler is bad but be careful not to ove3r pressureize the cooler this could damage it and caust it to leak. 15 to 30 psi should be plenty.
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Your A8 uses an Orifice tube to regulate the pressure between the two halves of your air conditioning system. A hissing sound is normal after a shut down as the system equalises. Usually lasts about a minute and is more noticeable on warmer days.
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