Strange Coolant Related Query - burst tank.

Post by **t1m-m** » 20 Sep 2006, 18:54

Looking for some help.

My T25 has been bubbling air in the expansion tank for about six months - it doesn't use any coolant and wasn't overheating.

Was suggested that my pressure cap could be opening too soon perhaps hiding an overpressure problem caused by a blown head gasket or cracked liner. So I borrowed a used pressure cap (thought to be good). took the van for a run - still bubbling in the expansion tank but still not overheating.

Tried bleeding system at the front rad' bleed screw - whilst doing so the coolant temp shot up - and the rad fan, which has always worked previously when in traffic, didn't - Coolant pressure tank then blew up like a balloon and burst.

Oh! I thought - looks like a head gasket I thought - boo hoo.

However in desperate hope that it wasn't so I bought a new pressure cap and a new pressure tank - & lo no more bubbles in expansion tank and no more overheating under normal and up hill driving as before (tho' still need to fix the now failed rad fan because temp rises as it should when in traffic).

Any ideas why my pressure tank may have exploded if not a blown head gasket or cracked liner??? And why should it have seemed to have fixed itself??????????? (Don't beleive in things 'fixing themselves' - not logical).

Thanks in anticipation.

Post by **kevtherev** » 20 Sep 2006, 19:00

vans fixing themselves....it's well documented

Post by **Dan Wood** » 20 Sep 2006, 20:16

Physcis in action maybe?

Water not under pressure boils at around 100 degrees.... (antifreeze will probably change that a bit but you get the idea!)

Water under pressure can be hotter before it boils.

So my theory is you had a sealed, pressurised system (maybe with some air in it?) and when you opened the bleed valve the pressure dropped enough to either:

1. Allow hot air in the coolant to expand rapidly....

or

2. Allow the 'superheated' water to boil suddenly, releasing large amounts of steam and blowing up your tank...

Maybe even a combination of the two?

Anyway, good news is it seems to be better now.

Post by **t1m-m** » 20 Sep 2006, 20:38

I like the Physics in Action theory - sounds feasable. makes sense especially as (and I ommited to mention) that when attempting to bleed the front rad screw i unscrewed it a bit too far with the throttle wedged a little open - an action which resulted in a spectacular fountain of coolant. Result as you suggest rapid lowering of pressure and lots of air in the system. Here's the result (if attachment works):

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