Coolant over pressurising.

[JimR]

I have burst two hoses in a week on my 8v digifant, heater matrix return hose and water pump to metal water pipe (how difficult to change!), on further inspection, my coolant hoses are getting rock hard when the car is warmed up. I took the expansion tank cap off and there is a pink sludge in the bottle and all over the cap, I'm assuming this is causing a blockage somewhere, does anyone have any ideas of how I might flush it out or what may have caused it? I'll put up some pics in an hour to illustrate what I mean. Head gasket was changed 1000 miles ago and before I bought the car so hopefully can rule that out but is an oil cooler failure likely?
Thanks in advance
James

[Jimmyrallye]

Had this o my first mk 2 golf gti i burst pipes when i changed them it kept presure rising out the 2 little holes in the expansion tank never got to the problem of it ... Just carried a 2 litre bottle of water round with me

[dadrathers]

Just follow RJ's guide as here:

http://www.golfgtiforum.co.uk/index.php?topic=106380.0

[JimR]

As you can see, oil is clean so anyone's guess,
Cheers
James

[Bandit127]

As you can see, oil is clean so anyone's guess,
Cheers
James

My guess is that the coolant has emulsified oil in it and that has blocked the cap (which is actually a pressure relief valve).

I would get a test on the coolant for combustion products. If there are none there, I would flush the old stuff out and replace. Put a new cap on (about £8 from VW?) and see what you get.

I come from the old school, the way we used to test for a combustion to water channel leak was to take the cap off and watch the water level. If it goes up and down slowly you have a leak. HG probably.

You have 2 chances with that IMO and one of them is not good... 

[JC]

before the old doom and gloom HG monsters come in, dont forget about your Oil cooler can give the same symptoms 

[raferackstraw]

coolant can go to sludge if not mixed with water and used in engines in more temperate climates, its possible some has used unmixed coolant which inturn has blocked the cap.
give it a full flush

[JimR]

As you can see, oil is clean so anyone's guess,
Cheers
James

My guess is that the coolant has emulsified oil in it and that has blocked the cap (which is actually a pressure relief valve).

I would get a test on the coolant for combustion products. If there are none there, I would flush the old stuff out and replace. Put a new cap on (about £8 from VW?) and see what you get.

I come from the old school, the way we used to test for a combustion to water channel leak was to take the cap off and watch the water level. If it goes up and down slowly you have a leak. HG probably.

You have 2 chances with that IMO and one of them is not good... 

I have run it up without the cap, it just rises then boils over, if I run with the cap on it gets highly pressurised then spits the water out of the cap. I'm kinda hoping this sludge is maybe blocking the water channels in the block and creating the pressure, I'll flush it out and report back.
Any suggestions on any additives to put in?

[JMallows]

Not sure on this, i'm not great with these things! When i did my coolant hoses, i filled up the water, ran the car and it did exactl what you said, rised up and boiled over. I drained it out, filled up so the expansion tank had a bit of water in it, then ran it, you can see the air coming out the expansion hose, then eventually it stopped, filled up the tank and all good.

I think what happens is when you fill up, there is an air block, and as the air goes round it pushes the coolant, hence coming out the top of the bottle. If the lid was on, it wouldnt be able to escape cos of the sludge, and pressurise.

Check the link abovve, it sorted it for me

[JimR]

A bit of an update, that pink sludge is some remnants of oil, I mixed some in with some water and lo and behold, rainbows. I flushed the system with a hosepipe and a fair bit of sludge came out. After this I took the heater matrix return hose off, bunged the metal water pipe and ran the hose backwards through the matrix, ALOT of air came up through the header tank do I assume a fairly large airlock was causing my pressure woes. I've bought some holts 2 stage coolant flush and will run that through tomorrow and refill with 50/50 mix, hopefully that will be the end of it!!
Thanks for all the replies.
James