Finished the engine swap just now and everything is fine apart from the coolant keeps boiling, I'm just using water at the moment as i knew there would be a few leaks. What leaks there were have now been fixed, if i run the car for about 4 minutes the coolant starts to boil until it blasts out the over flow or if the lid is off its comes out like a volcano its damn right dangerous!

Iv tried bleeding it from the heater valve and tried squeezing the radiator pipes but it keeps doing it..

What could be causing it? Trapped air? Theres no steam coming from the exhaust so i dont think its a problem with the head/gasket.

you should check the thermostat first could be not opening,and is the fan cutting in?should cut in twice to prevent overheating.

Take the thermostat out ??

It does this before the fan even thinks about cutting in! I'll go back out in a minute and take the stat out see if it still does it.

The thermostat is new

Keep the ideas coming!

sounds like the thermostat is stuck shut or the tank cap isn't sealing.

yeh MK4 polo engines have problem with thermostat elbow they brake inside !!

timing all ok?any ideas of when the water pump was last changed?good oil pressure?

I'm using an ABU engine now and a mk3 GT thermostat housing (brand new) so it should work perfectly.

i had this exact problem not too long ago

and it was the thermostat

Sounds hopeful, i'll take it out in a minute once i can feel my hands

Ok stat is out and it still does it!!!

Its not coming out of the cap on the coolant bottle but the actual pressure release valve!

Any more ideas, look like the head gasket has gone.

water pump impeler fooked?

I took the water pump off and there were no broken bits..

I really need to diagnose this now.

blocked rad?

Rad was working fine before and the bottom pipe is cool and the top is warm so that shows its working.

With the water hot enough to boil over, you would expect the bottom hose to be warm aswell, no?

Suggesting the thermostat?

just to add after its done its boiling thing and i have turned the engine off you can hear it making some really wierd noises, like gurgles if thats the right word? So maybe trapped air but how the hell do i remove trapped air, having tried bleeding it with the heater valve and running it with the lid off.

the bottom hose is cool, thats with the stat removed. I didnt check it with the stat in.

Also I'm just using water at the minute as i didn't want to loose antifreeze from a leak, surely this isn't normal though. I know the antifreeze stops the coolant from boiling too early but iv heard of people using water all the time without problems?

Ash

I can't see that being the issue, i used just water for a couple of years

mine was doing this a second ago

turns out the plug to the fan motor came disconected somehow

Even if the thermostat is new it could be faulty? Or have you used it before with no probs?

mine was doing this a second ago

turns out the plug to the fan motor came disconected somehow

What so it overheated?

I'm going to get some new clocks tomorrow so i can see what temp its boiling over at and then go from there. It may be that the engine is running hot, the only reason for that would be the dizzy timing as its not been set yet. I have been running it with the thermostat out and it still boiled over.

that is really weird , have you tried squeeking the hoses ??