Expansion tank replaced - twice - still leaking coolant!

Hi Guys,

I replaced my expansion tank a few months ago as I was leaking coolant.

The new tank + cap then started leaking too and was found to be leaking from the cap.

I've bought a new cap + tank and it's still leaking from the cap!

After a run (i.e. engine at full temp) there is a hissing coming from the cap.

However if you turn the tank so that the coolant is covering the cap (i.e. could leak if it wanted to) nothing comes out!? (Engine off)

All I can think of is that the system is slightly over pressurised and when I go round a corner abit of coolant gets out, however over a long trip quite abit comes out and it goes from max to min!

Ideas?

PS: Cylinders were pressure tested at 175-180 PSI IIRC (I was told this was fine, and normal).

Cheers.

When cold the level should be at min.  Hissing is normal, if you look at the underside of the cap you can see that it is designed to release pressure.  Do you have the correct cooland mix?

Coolant mix is something around 40% anti-freeze.

So the coolant level when cold should be min, so whats the max point for? When hot?

I will bring it down to the min level and see what happens then!

Yip, exactly when it's hot it should go up to the max. Mix sounds good to me.
Jj

hello guys! the coolant cap is ment to have a point at which it releases the pressure in the system to stop the rad or the tank blowing up! it sounds like a blocked sytem to me  i.e faulty rad try putting some rad flush through her if not get another rad! i hope this helped

Would be worth flushing the whole system out , and check water pump/ replace the thermostat and fan. Temp sender,   sounds like the cap is doing it's job , when engine is on idle with cap off is there a flow of water into the expansion bottle ?

mk1jim said

Would be worth flushing the whole system out , and check water pump/ replace the thermostat and fan. Temp sender,   sounds like the cap is doing it's job , when engine is on idle with cap off is there a flow of water into the expansion bottle ?

Yep.

It was flushed 6/7 months ago when I replaced a number of hoses and the thermostat and it was pretty much clean (a very small amount of particles at the bottom of the bucket).

Engine temp stays pretty much bang smack in the middle, doesn't overheat etc.

Hopefully it was just me overfilling it, I will see once I use it again!

Keep us updated, hope you sort it, also keep an eye on the regional section having another Bristol meet soon, if you fancy coming along

Cheers Rich

put a genuine vw tank on, see if that helps. i find that the pattern tanks are rubbish and leak!