mk3 ABF coolant* boiling over

[aminorthreat1]

ever since i flushed and replaced the coolant in my 16v after being driven hard for 5-6 miles the coolant boils over and out the expansion tank. engine temp is normal, so i was worried it was the head gasket. so ive done everything, compression test, cylinder leakage test, and checked for exhaust gas leaking into the coolant. none of which indicated a leaky head gasket. i did manage to squeeze some air out of the pipes once the hole thing had cooled down and i had encountered an airlock when changing the anti-freeze. but with the amount of air i've squeezed out and amount ive topped up the coolant im fairly sure i've got rid of the airlock. so now im thinking theres maybe a block in the radiator? anyone else have any ideas?

[VWstevo]

ever since i flushed and replaced the coolant in my 16v after being driven hard for 5-6 miles the coolant boils over and out the expansion tank. engine temp is normal, so i was worried it was the head gasket. so ive done everything, compression test, cylinder leakage test, and checked for exhaust gas leaking into the coolant. none of which indicated a leaky head gasket. i did manage to squeeze some air out of the pipes once the hole thing had cooled down and i had encountered an airlock when changing the anti-freeze. but with the amount of air i've squeezed out and amount ive topped up the coolant im fairly sure i've got rid of the airlock. so now im thinking theres maybe a block in the radiator? anyone else have any ideas?

Hi mate

mite be the water pump buddy mine doing the same and i've just done my head gasket and timing etc. Got a new pump today so fitting it tonight. It because the engine is getting to hot and the pump is not opening the thermo quick enough so it pushes the hot water back and out of the overflow on the expansion tank.

Water pump £21 includes Vat from GSF

[aminorthreat1]

cheers mate, ill look into that. also just had a thought, is the PAS and water pump ran off the same belt? coz my PAS belt is slipping on full lock and needs tightening. i know theres two belts down there (besides the timing belt) one runs the alternator and the other runs the AC compressor.

[VWstevo]

cheers mate, ill look into that. also just had a thought, is the PAS and water pump ran off the same belt? coz my PAS belt is slipping on full lock and needs tightening. i know theres two belts down there (besides the timing belt) one runs the alternator and the other runs the AC compressor.

I'm not too sure buddy, I changed the thermo the other day and the power steering pump and I didn't see the water pump attached to the PAS. Have you tried tightening it up mind did the same and I tightened it up and it was fine.

[aminorthreat1]

just had a look, the outside belt drives the PAS and waterpump, im guessing the bottom one is the PAS pump (the one with the tensioner) and it looks as if its fully tightened. i'll have to jack it up to get a proper look since the things on its arse with a vr6 splitter so acces isn't easy, so i could be totally wrong lol. but i'll have a good look at it this weekend.

[AudiA8Quattro]

First try changing the expansion cap.

[jezza16v]

+1, sounds like the o ring in the expansion tank cap is perished or 'nipped'.

[aminorthreat1]

is that a common fault on them? ive heard something about the pumps having plastic fins which are pretty weak, cant remember if that was the mk3's or not tho.
the cars been sat a good 3 hours and the engine is cool but the coolant is still right to the top of the expansion tank, it was filled to just above min.

[AudiA8Quattro]

How long does it take for the pressure to build up from cold?

[aminorthreat1]

few mins, not long. maybe 5. sometimes the temp gauge can take a while to rise as well but i was thinking thats just the new coolant, but 4 miles normal driving before it climbs?