Hey people,

After some thoughts on what the cause of this could be.

Car gets up to temp and stays there fine, heater is warm.

Head checked/skimmed/HG replaced.

Coolant cap replaced.

System pressurises too much, meaning fluid is relieved from the header tank...

What would cause the system to do this?

Would I be right in thinking a broken up plastic water pump would create poor circulation causing a pressure build up?

Any help appreciated...

If the CTS is reading fine then it's probably not getting too hot causing excessive pressure, under ~1 bar you need to get a 50:50 mix to ~130'C to turn liquid to vapour.

Check the header tank cap is good and the seal is intact- start with the cheap stuff first.

Under what conditions does it happen?

I doubt that the water pump is the cause of this problem.

If everything else is in tact (HG is OK, no porous block or head, which is unlikely anyway) The most likely cause is that there is too much coolant in the system.

Do you have the standard radiator and header tank? If so, make sure that it is no more than at the 'minimum' level when the engine is cold. As the coolant warms up and expands, it SHOULDN'T go any higher than the 'maximum' mark.

if you have changed that rad and/or the tank, I would suggest that you allow it to push out what it 'thinks' to be excess coolant, note the level when it is cold and then in future do not top it up any higher than that level.

Regards.

Thanks for the replies.

So it's a totally standard car, standard rad/tank etc.

I topped it up Tuesday, and drove 20 miles to work, got in it to go home and level was low enough to put the warning on.

Topped it up, drove home - so that's 20 more miles.

Next day I did 20 miles pottering, around town; then fitted a new genuine coolant cap.

Drove 20 miles to work; then 20 miles back.

Thursday, another 40 miles, fine.

Drove to work and back again yesterday, another 40 miles, things are looking up.

Drove a mile to get fuel, fine, went from fuel station to McDonald's last night, as I pulled out the drive thru the warning came on - level was low again.

Topped it up, drove 20 miles to work this morning; fine; got in car to go home and level low again.

It's a bit inconsistent to say the least.

Driving is around 5 miles across town, if that, then b roads around 50-60mph, and about 8 miles a road.

Temperature is a bit inconsistent; it runs around 80 degrees, which is a little low but being cold and a diesel I don't know if this is about right?

I did notice it was fluctuating a bit today; never goes above 90 though, hovers between, but maybe this is just the stat opening and closing?

Just had it idling away now; and the small return hose to header tank appears to be bubbling, like it's mainly air, meant to be a nice steady stream of coolant isn't it?

After most journeys I will stop and you can hear the header tank "venting" like it's relieving pressure; it's a little hard to see if it's coming out the proper overflow or it's a damaged bottle.

The aeration in the small return hose is my concern.

IMO I think the pump is ok, aswel as the stat.

I thought VW cooling systems were generally good for self bleeding?

Any input appreciated. Might try a drain and a vacuum fill?

To add - it pushes it out and settles to a level when cold, this is below the minimum and throws the warning on.

IIRC if you let it warm up, then key off and on to reset the warning, as it's expanded the level is then ok and no warning, but I havnt tried running it like this for a period of time to see if it drops further.

This was after a drive, up to temp. Level had risen as I probably topped it up a little too much.

http://i963.photobucket.com/albums/ae114/h...5E275503934.mp4

I then proceeded to take the cap off with it running and release the extra fluid, which then settled down to the level in video, let it tick over with cap off for a few minutes with heater on full.

This video also shows the aeration I was on about in the small return pipe..any ideas?

http://i963.photobucket.com/albums/ae114/h...5E2B29ADE5C.mp4

EDIT:

Let it cool for a few hours, level was just on the minimum, started up and within 2 mins of idling the level had dropped down enough to put the warning on...I'm lost now...airlock ???

Edited 3 November, 201213 yr by harris.racing

the fluid is going somewhere! whats the oil level like?

if there are any leaks however small it will release as steam and can be hard to notice, will overheat as it will get locally hot and not get hot at the thermostat- so the coolant will get very hot and cause the pressure cap to open and release the pressure- even though the rest of the cooling system shows lower temps and radiator be cold.

Oil and coolant not mixing, coolant doesn't smell like combustion either.

It pressurises and comes out the header I think!

you must have a small leak on the header part of the system. is it coming out of the header but the bottom rad pipe cold?

water pump may also be at fault for this- a way to check is to see if it overheats on idle- if it does it on idle its not the pump, leave it running for a while. it is the water pump if it only does it under load.

Definately leaks out the header tank pressure relief thing.

Just drove back from work and was hissing and you could see where the excess coolant had ran down from the tank.

So why is it pressurising is the question.

Hoses both warm so assume stat to be ok.

It's diesel. Not sure how long will take idling to get it hot?

yes, i know its coming out of the header as thats the pressure relief- its doing its job- but i fear you are also leaking from elsewhere causing it to do that! its not leaking from the matrix is it? - they do tend to fail on older vws.

should take quite a while to get hot on idle as the engine isnt working hard- so if it doesnt take long then you have a leak from somewhere causing it to get hot and over pressurise the system causing the header tank cap to open.

if it starts to get mega hot well quick when you take it for a drive it will be the pump.

It seems ti me to be time to invest in a combustion 'sniffer' test, plus, maybe a compression test, that coolant has got to be going somewhere!

I know that you said there is no combustion smell from the coolant, but it may just be in this case, that the human nose isn't sensitive enough to pick it up.

I'm not quite sure what KiZ is saying, as I see it, the only reason that the coolant wouldn't get hot at the thermostat is if the level had fallen below that of the 'stat, unless I am underestimating the amount of water that you are having to top it up by.

Before you do anything too drastic or spend serious money, you could try running it without the 'stat in for a day or two, that way, at least you have eliminated one (probably unlikely) possibility for no actual cost.

Regards.

Have just that a bit of a better look.

Definately comes from header tank, can't see other leaks.

Top & bottom hose get warm, but also get hard.

Has been driven at sat ticking over for 15 mins and didn't go above 80 degrees.

If you rev it with the cap off, the coolant gets a bit "froffy" caused by the flow of coolant from the top return hose rushing in.

It has had head skimmed and a HG, but obviously this isn't a guarantee it's not the issue.

What would a compression test tell me? The leak must be fairly minimal if it is HG, no white smoke and tank doesn't bubble like a fish tank?

Just trying to think logically here...

If it builds up pressure, then loses coolant due to it expanding and going out of the "degas" tank..

So pressure caused by:

Coolant expansion, with heat...but isn't running hot

A restriction?

Just confused, the bubbles going through the small return hose may just go that way as its the highest point & air rises to it?

what i was trying to get across is that I've seen on 2 different occasions a small hole in a hose away from the thermostat and close to the header tank, this has allowed the coolant to steam away and created a hot spot which got the coolant very hot and created a lot of pressure- this in turn made the pressure cap open and release the pressure..... and the coolant.

the other thing i was trying to say was that an engine on idle will not get hot very quick! it will take an age unless therenis a problem like I've described above. if it doesnt get hot then the problem only exists when the engine is under load- thus making me think its the water pump which has failed as the water in the engine creates the hot spot which pressurises the system as the water flow wont get to the radiator to cool it down.

I have a new pump and thermostat anyway - got it with the car.

Kiz wanna earn some money? Haha

so you got a new pump with the car?

sounds like the previous owner knew this was the problem!

what car is it?

Yeah he was fully aware of the problem, I bought it off a friend lol!

Golf TDI, 90hp not a PD.

I've got the same engine in my skoda. AGR or ALH???

good luck with that! they are a common failure as the early mk4 golf tdi and 1.8t engines had a plastic impellered water pump - now all metal impellered!

its a timing belt type - means you have to use vagcom to time the diesel pump up afterwards- a bugger of a job i never want to do again I'm afraid - once was enough for me as space is a premium to get at the bloody thing and in this weather youd be best off taking it to a garage

Not sure on code mate, I'll have a look, where is it? Lol.

I do hope it is the pump but I still think its gonna be HG as just my luck!

Ah should only take 3-4 hours, got vagcom..should be ok

3.7 hrs for the waterpump, Autodata times :-)

on the V5 is the easiest place to look. or theres the data plate in the engine bay or on the block itself.

id have a sniff test done to see if the gaskets gone or if you keep driving it then it may keep overheating and do the headgasket again and/or warp the head

Its an ALH according to the reg plate :-D

Doesn't get hot though, which is odd. Unless its hot just not by the sensor lol.

Got a spare head anywho.

Where can i get a sniff test? How reliable are they?

3.7 hrs for the waterpump, Autodata times :-)

yer for a garage!!! do it without a ramp on your driveway in the cold and i bet that time goes up!

And yes nick, hot just not near the sensor! water isnt flowing so its hot inside the engine causing the problem. Most garages should have the equipment