Coolant bubbling

[stevespic]

Help Please, Dose any body know what this may be... When i switch the engine off on my 944S2 i can hear the coolant bubbling... not everytime but may be 5 out of 10 times !

 

[Guest]

Try running the engine with the expansion tank cap off ( cold engine obviously)....Does the water bubble? if not, then its probably not head gasket etc, so I would suggest buying a new cap, as yours may not be releasing the pressure properly

I'm having a few coolant worries at the moment, but am gonna start with a new cap....

 

[sawood12]

Might not be coolant, but the fuel scavange system. There is a small pump that runs after you switch off and pumps fuel from the fuel rail back into the fuel tank. The noise can sometimes sound like bubbling I suppose.

 

[stevespic]

Thanks for the that information and advice, i have just been out and checked the coolant pressure cap and noticed that it has a very small split in the seal about 4mm long, when i realesed and removed the cap there was was no pressure build up at all which i guess is a good thing...

 

[John Sims]

ORIGINAL: sawood12

..... the fuel scavange system. There is a small pump that runs after you switch off and pumps fuel from the fuel rail back into the fuel tank. .......

Damn, you learn something new every day. Why do you get covered in fuel when you take the pipes off the fuel rail then?

 

[peanut]

cos you are supposed to remove fuel pump fuse and run the engine till she cuts out which relieves the pressure !
never heard of a secondary fuel pump ? what models is that on then ?

re the bubbling sound it could be air in the system due to the split but I would make certain that the electric radiator fan is still running for 10 minutes or so when you switch off the engine . If it doesn't the engine temperature continues to rise several minutes after you switch off. The increased pressure can cause bubbling sound in the pipes and heater radiator.
When this happened to me, soon afterwards my head gasket went ! £0000000 so I would strongly advise you check out your radiator sensor, fuse and fan operation

 

[John Sims]

ORIGINAL: peanut

....never heard of a secondary fuel pump ? what models is that on then ?....

Quite! [8|]

 

[sawood12]

ORIGINAL: John Sims

ORIGINAL: sawood12

..... the fuel scavange system. There is a small pump that runs after you switch off and pumps fuel from the fuel rail back into the fuel tank. .......

Damn, you learn something new every day. Why do you get covered in fuel when you take the pipes off the fuel rail then?

Because it only relieves the pressure in the fuel rail and doesn't totally evacuate the fuel pipes leaving them primed for the next start up. That's why you have two fuel pipes, one is the return pipe. You have to really listen out for it. I heard it once when the car was parked uphill and I could hear the pump and the scavanged fuel actually tinkling as it drained into the fuel tank behind me. I had to pop off to the toilet shortly after!

 

[peanut]

Thats curious I just took my S2 for a 25 mile blast and she was quite hot when I got back
I switched the engine off and could hear the engine tinkling but no fans ? ( mine has 2x fans like the turbo )
When I switched the ignition to aux sure enough both fans fire up big time like a helicopter.
Shouldn't they be direct fed from the battery so they run after switch off until the rad sensor switches them off ? Otherwise whats the point ?

 

[sawood12]

Yes that's what the fans are supposed to do so maybe your car wasn't hot enough to kick them in. There is nothing wrong with your rad stat as when it fails it fails safe so the fans will run until your battery drains. The tinkling noise i've heard before I think is coming from fuel being returned to the tank but i'm not sure if this is driven by a pump or just by the pressure in the fuel system equalising once you switch the engine off.