Boiling hot MK2

[TC]

Been trying to sort an overheating problem with my Digi '92 MK2 with 105K.  It's fine when it's standing, the water temp sits just below 1/2 way and the fan cuts in and out as it should and it's up to full pressure.  As soon as I drive it above about 50mph or find myself hitting a hill the water temp flys up and boils the system then empties through the overflow in the header tank.  The thermostat opens and the bottom pipe to the rad gets hot as well but would this get hot anyway as it backs up from the top of the rad?
Water pump works fine. Oil temp is fine.
Head gasket on the way out but no oil in the water and no water in the oil?
Any ideas as it's real

Cheers

[16v Matt]

If you're sure the thermostat is'nt buggered, then it sounds like head gasket time

[16v Matt]

BTW why do you say the h g is on the way out?

[TC]

thought it could be, suppose a pressure test on the water system would always tell.
Many Thanks

[TC]

Not sure, i've had 5 MK2's 8's and 16's but never really had a problem with over heating, just thought this may be one of the only other things it could be but it's got a nice history and low miles so in theory it shouldn't be but suppose you never know who's had their hands on it.

[Dizzie]

the large pipe on the bottom of the rad should always be hot when the engine is up to opperating temp...

sounds to me you have a bottle neck somewhere. when you idle the pressure of the water is low. when the engine speed increases it spins the water pump faster increasing the pressure the coolent circles the system. if it can't get through it could back up through the pipes and overflow the tank...

just an idea.

[TC]

Cheers,
It's also a little odd, or is it normal for a later MK2, not to have a cross over pipe before it runs through the bulkhead and through the matrix as earlier models have this and I know it can block easily as it's usually quite thin?

[Veedubgt18v]

nah its not normal to be missing the crossover pipe. sounds like your head gasket is on its way out, i had similar symptoms, get the coolant fluid checked for exhaust gas. but try replacing the thermostat first and back flushing the coolant system to remove any crap. see if that helps

[TC]

Nice one cheers will try that, sounds like it could be that time

[keefusg60]

I'd change the thermostat first, as it's cheap and relatively easy, and I had similar issues with mine and changed the thermostat in case it sorted it, and it did.