As title really.

On the road/track the car doesn't get hot, even pulling 7k+ in 5th, and is fine sitting in traffic etc as long as you like, but once you stop and turn the engine off, it bubbles over quite a bit- Regardless of this though, temp gauge doesn't show it overheating (it does work, leaving the rad fan off shows that!)

Immediate thought was the header tank cap, so changed it for an uprated one and its the same problem.

Removed water cooling to the turbo and the modine to see if that had an effect- Nope.

The header tank and radiator is smaller than a stock Cossie one (Engine conversion), but while it deffo doesn't overheat normally, will this be why it boils over when the engine is off?

There's no swirlpot, but I don't know if they're a gimmick or not anyhow.

Any ideas? Doing by head in to be fair.

 

This is a strange one, hope you get it sorted,

 

Pressure test the cooling system.
Either it is leaking or there is an air lock.

 

Had this issue on my RS turbo, updated the expansion tank to a Baileys model and all was sorted.

It was the plastic thread on the expansion tank which was the problem.

 

not enough expansion volume in your system?

 

that's what i was going to suggest, especially if its a cooling system which has been thrown together with different parts from diferent systems

 

how about fitting en electric water pump on a timer to keep water moving after it's turned off to let it cool down longer without pressurising?

 

That was what my first thought was. I raised the header tank bottle as high as poss today too, to remove the chances of an airlock.

BUT today, on a 20mile drive mixed of normal and 7k rpm caning, while it didn't overheat, in fact the temp gauge didn't move beyond normal, it managed to (though mostly once stopped), totally empty the header tank (possibly more).

This mean it's actually a dead HG and it's getting gradually worse?

I got a trackday on Sunday! I can do a HG swap Fri/Sat if I can get the parts before then, IF it is that...

 

if your still driving it, cant you get it to a garage and have the cooling system pressure tested?

 

Not wanting to sound negative here but mine had the same issue, sat at normal temp etc. Pull up and it just overflowed everywhere rushing out the expansion tank.

Whipped the head off to find a nackard gasket. Fingers crossed its just an air lock tho...

 

Did some more 'testing' and pretty sure it's a HG now! Combined with a few other issues I reckon...

Basically, I switched the header tank that I didn't trust for an Audi 1.8T one, which has a pressure cap rating of 2bar!

Suddenly, no leaking out of pressure cap, but top hose was suddenly ROCK fucking solid, and it was actually pushing small bubbles and hissing from the gaskets around the water pump (the ones that join to the head and block), it was THAT much pressure!

Overheats now, and quickly too, HG is deffo gone.

Odd one though, overheats, BUT bottom hose is still as good as stone cold- Surely for it to get overheating hot, it'd all be hot as hell? I reckon either rad or something is partially blocked, or water pump is fucked, or something.

Shame now it's gone bad enough to not make it drivable to the workshop, feck.

 

Had similar on a Sierra years ago, the guy had fitted head gasket, radiator, water pump & thermostat. It was the return to the header tank blocked, drill bit through the return on the header tank. Fixed!

You've changed the header tank to rule it out though.

Have you had the thermostat out to test it?

 

Not checked the stat yet, but now I think back, this reminds me of when one of my old Mondeos stat's knackered up! I'll be replacing or removing it, maybe remove actually due to the use, or at least drill holes in it.

BUT stat or not, the shitload of pressure must be from the engine, so methinks the head gasket is proper blown now too.

 

Does appear so!

 

What about a blocked radiator?
If its hot at the top and cold at the bootom then does that not mean the coolant is not flowing through causing it to pressurise up and blow all the water out the header tank.

I would try taking both top and bottom hose's off the radiator and put a hose in the top see if anything comes out the bottom.

 

try running compressed air thriyvh a few of the components of the cooling system one at a time to find and mYbe blow out blockage, also try evacuating air from system before refilling so garenteing no air locks. goodluck

 

UPDATE!

Awesome news, and a good example of never automatically thinking the worst!

Today, just to see if it was possible to stop it overheating enough to drive it to the workshop, I removed the thermostat...

It was FUCKED, the inner section looked like a bullet fired from a gun, with bad score marks all along it where it had been scraping on the outer section trying to move.
It was a proper Motorcraft one btw.

Removed it, bled and refilled the system, all seemed fine.

Drove it for ~20 miles inc a few squirts (inc up to 5k in 5th) and it was fine, didn't get hot, didn't do a thing.

Once got back, turned it off and it didn't try to bubble over, the header tank level was as high as you'd expect it, all seemed ok.

After a minute we undid the header tank cap (bearing in mind this was a 2bar Audi 1.8T one so could go off like a bomb lol) and the pressure was very low, in fact less than in any time since I've owned the thing.

So yeah, it seems, it was purely a massively shagged thermostat that was getting worse,
and the heat alone was causing the pressure and bubbling and so on.

Good old YBs too, reminded me of another reason I love 'em- Most engines usually crap their pants at the first sign of overheating, but nope, it's loving it.

Hopefully at least, that is that...

 

sweet

 

Great success [borat]

I had a thermostat stick on my VR6 on a trackday, but it was showing red hot on the gauge, end of play.

 

that's the problem with the YB iirc that the temperature sender for the gauge is downstream of the thermostat so doesn't help with the diagnosis