Hissing from expansion tank

[danielz000]

Hi Guys,

I've been battling a coolant leak for a while, thought I'd finally fixed the problem (need to check the coolant again tonight) but last night after turning off the engine I noticed a hissing noise coming from the expansion tank.

It was the first time I've noticed the noise... The car had been driven for about 15 minutes...

Being the brave soul that I am I removed the cap and found that there was no pressure in the tank and no scalding on my hands.

Is this normal? Shouldn't there be pressure in the system and why would it hiss?

I don't think the tank is cracked (although I will recheck it...) but I've read a few things about a valves in the caps... Are they there to let off excess pressure? Is that what I heard? Should I expect the hissing to stop once the pressure has levelled off?

I'm a bit worried that some of the coolant could be evaporating and/or the system not performing as well as it should due to a lack of pressure...

 

[slayllian]

I have this exact same sound for a few seconds after I shut the engine down, not sure if its normal though? :?

 

[danielz000]

I have this exact same sound for a few seconds after I shut the engine down, not sure if its normal though? :?

Well it's a bit of a worry for me as I was lead to believe that the system was kept under pressure to enable the coolant to reach higher temperatures before boiling/evaporating...

 

[yippeekiay]

Get yourself a shiny new cap and seal...or just the seal as that's probably perished or gone hard with age and not sealing properly

 

[slayllian]

cheers yipp, i will try that myself! k:

 

[yippeekiay]

Don't actually know if it has a seal as I've never looked to be honest, pretty much assuming it has as that's the first thing I'd be looking at with any sort of leak from a cap/lid etc....lol.

This wisdom comes from many years of being on this wonderfull planet...pmsl ;p

 

[danielz000]

Don't actually know if it has a seal as I've never looked to be honest, pretty much assuming it has as that's the first thing I'd be looking at with any sort of leak from a cap/lid etc....lol.

This wisdom comes from many years of being on this wonderfull planet...pmsl ;p

Cheers buddy! Can you confirm there shouldn't be leaking/hissing? Any idea where I can get one of these shiny new caps from? ;-)

 

[martinthrapston]

There should be no hissing from cap when engine is running ,cap needs replacing if this happens.

 

[danielz000]

Cheers Dude!

Do they have a valve of some sort in them or did I imagine I read that?

 

[mix2000]

Yes they do have a pressure relief valve.

 

[danielz000]

Hi guys,

So I fixed too leaks on my Puma and have to concede now that there is at least a third... I did think it could of been the expansion tank as I could hear hissing coming from it but on a second inspection the noise appears to be coming from the air conditioning. Does that make sense given the location?

Unfortunately I'm still (slowly losing coolant), so if anyone can suggest a way for me to find the leak I'd be grateful... I can't see anything obvious which is leading me to suspect the HG or matrix but I find it hard to believe it could be either of these...

I was thinking to some how try and create pressure in the system while it's cold in an attempt to force a leak but stop it drying up, hopefully that would make it move visible... Any other ideas / suggestions?

 

[goodnitegirl]

Hi guys,

So I fixed too leaks on my Puma and have to concede now that there is at least a third... I did think it could of been the expansion tank as I could hear hissing coming from it but on a second inspection the noise appears to be coming from the air conditioning. Does that make sense given the location?

Unfortunately I'm still (slowly losing coolant), so if anyone can suggest a way for me to find the leak I'd be grateful... I can't see anything obvious which is leading me to suspect the HG or matrix but I find it hard to believe it could be either of these...

I was thinking to some how try and create pressure in the system while it's cold in an attempt to force a leak but stop it drying up, hopefully that would make it move visible... Any other ideas / suggestions?

Mine hisses after the air con has been on and you switch off, my air con man said it was normal and was something to do with the system pressurising or something. I initially thought it was from the coolant so got a new cap just to be on the safe side it was like about £4.00. :lol:

 

[slayllian]

Mine hisses after the air con has been on and you switch off, my air con man said it was normal and was something to do with the system pressurising or something. I initially thought it was from the coolant so got a new cap just to be on the safe side it was like about £4.00. :lol:

Since found out mine is exactly the same and occurs only after the aircon has been run :grin: