Overheating probs, scratching head

[whytie]

Had an overheating issue, at knockhill on Sunday.

After the first run the water in the expansion tank was pressurising and overflowing, temps were also sky high and was revving on its own. I let it cool down and topped up the water then blead the system. I let it idle for ages and all was well fans were on ect. I had also lost 3rd and 4th gear so day was over.

We drove the car home and all temps were spot on and that was about a 1 hour journey. I went out today to take the gearbox off and noticed there isn't really anything in the expansion tank. Took radiator cap of and looks pretty empty? First guess would be head gasket but the oil looks good especially after a hour journey home.

Don't think water pump as it must of been working on way home? Can't see an obvious leaks? I'll borrow a pressure tester tomorrow and test for leaks.

Any thoughts?

 

[GTI_R]

sticky thermostat maybe

 

[whytie]

It drove there fine, wasn't until flying round track it went mental. Then drove home fine. But it's losing water somewhere

 

[pulsarboby]

if you cant see any visible leaks then its more than likely blown a head gasket.
you dont always get oil and water mixing as it may have blown between cylinders in which case itll pump water straight out the ex valve and youll lose water
or likewise a blow between waterway and cylinder will result in same thing

try doing a compression test with one plug removed at a time then do it again with all 4 plugs removed and see if theres any difference between 2 readings
or do a cylinder leakage test or chemical test which will also indicate where prob lies

 

[Ghostie]

Put a pressure tester on the rad once topped up and look for the drips and if it's loosing pressure . If you can't see no drips on the floor remove the plugs and look in cylinders , try it with engine both hot and cold that will find ur leak

 

[PobodY]

Put a sniffer test on the radiator. - If there's exhaust gas in it, that's a bad thing.

 

[whytie]

if you cant see any visible leaks then its more than likely blown a head gasket.
you dont always get oil and water mixing as it may have blown between cylinders in which case itll pump water straight out the ex valve and youll lose water
or likewise a blow between waterway and cylinder will result in same thing

try doing a compression test with one plug removed at a time then do it again with all 4 plugs removed and see if theres any difference between 2 readings
or do a cylinder leakage test or chemical test which will also indicate where prob lies

what do you mean ex valve?

 

[Mr B]

colour difference of plugs & piston will be a give away if cylinder/cylinders drinking water well.
Many leaks can occur only when hot & under pressure thus little visual evidence early on in stationary/idling inspection.

 

[GTI_R]

what do you mean ex valve?

ex = exhaust

 

[whytie]

ex = exhaust

get yeah.

Ill pressure test it tomorrow but im sure there's no leaks. It's all a bit odd.

Think ill drop engine to do the gearbox this time, that way if I have a leak or need to do head gasket it will be easier.

What a pain in the ass, I just fitted a clutch to it on Saturday the day before. Was hoping to sell the car after Sunday.

 

[Fast Guy]

I've had plenty of the cooling hoses leak and only one of them (big one with spring in) has been noticeable, the others have been very sneaky and I've only known I had a leak when I heard a gurgling sound after switching off.

 

[vss irvine]

check the hoses first and the water pump when its out. Unless your 100% dont change the head gasket. In 14 years ive only ever done one headgasket. (apart from engine rebuilds).
Rad cap is another favourite. Buy a new one.