Air leaking noise from the engine bay

Just done a search but can't find anything that is related to my noise problem.

Came home park the car and notice air leaking sort of noise coming form the engine bay from the right hand side to be exact between the battery and the plenum. The noise was there for about 5-7 minutes after the car has been turn off completely. I looked for any lose hose etc but can't find the culprit.

There is no oil, water or fuel spray etc just sounds like air is leaking from somewhere

Any one has any idea? what is it cause and solution?

 

That would be leaking from the brake booster I would guess.

 

After 5 to 7 minutes it won't be air. More likely a pin hole leak in a coolant line.

Can't see steam? Try using a torch in a dark garage.

You can localise the noise by putting a short length of hose in your ear and probing the engine bay with the other end.

Still not sure? While the noise is there, remove the radiator cap ( very carefully ) and see if the noise stops.

 

Break booster hmmm will check that

No there is no steam what so ever but I will try to remove the radiator capp carefully ans see if it stops

 

I didn't think about a coolant leak, could be that. With the brake booster, after the noise has stopped give the brake pedal a push. If it's really hard on the first push then it is likely a leaking booster/piping for the booster.

 

Yes. aircon still works fine

Coolant leak hmm can't see any sign of the water etc.

Car been parked for about two hours now so went and press the break pedal and yes it was really hard pressed few times still hard. Fire up the car again press the break pedal again and its soft now. Turn off the car completely no leaking noise now.

So that confirms Break booster is the culprit?

 

Any chance its the fuel system?

 

well if its the fuel line I could see the fuel leak or at least smell the fuel before the car blows up.

So don't think so.

 

One possible reason why you don't have a hiss now is because the engine is cool, i.e. the coolant system is not fully pressurised.

Yours is a TT yes?

 

i was thinking more along the lines of the fuel line still being under pressure. and what you can hear is the FPR.