Hi Folks,

We run a 1.4 Mpi as my 17 year old sons first car - so it gets a pretty hard life.

A few weeks back he had a sudden loss of power whilst coming home late one night, went out to investigate and found all the coolant in the water so towed it home expecting to find a head gasket gone. Pulled it apart and it had actually popped a core plug, one of the ones under the rockers, hence all the coolant in the oil. As I already had the head off, checked it was flat and there was no leakage obvious on the gasket faces, reassembled with a new head gasket. Back together and it ran great, better than before in fact, only concern was a slight squeal from the ancillaries belt when cold. Leave it ticking over until the fan cuts in, all working OK, coolant level steady.

Was then fine for a couple of weeks (probably about 400 miles in all) but during the last week has started dumping its coolant out of the bottle overflow. This is like a gross loss, after a 12 mile drive to work he was adding 1.5 litres and the same again on getting back home.

Suspected the expansion bottle cap so replaced the cap and the bottle, refilled and took it for a test drive up a long steep hill thats about 5 miles from our place. Runs OK with the temp gauge at mid point until just clearing the top of the hill when the gauge races to the stop (say 10 seconds from mid to max) red light comes on and we stop. All the coolants been blown out the engine block via the expansion bottle and it takes 3.5 litres to refill.

Back on the drive refill and bleed, leave car ticking over till thermostat opens, rad gets hot, fan kicks in. What next?

Changed the water pump today as thought it might not be circulating at full flow, but no obvious problem with the old one when I got it off (now that was a bigger job than I was expecting involving much cursing). Also checked the thermostat in a can of water and no problems. Took it back out for a test and dumped the coolant at the top of the hill in exactly the same was as before.

Only other thing I can think of now is that the head might be cracked.

Anybody else had anything like this or got any ideas what else to try?

Thanks

DC

The coolant is obviously being pressurized by combustion process, or the wrong anti freeze has been used at some point, causing a partial blockage in the water ways. If G10 AF is mixed with G12 or vise versa, it forms a gel like substance. Even reverse flushing doesn't always clear it. So you will have to have a pressure test done on the coolant system. If that's OK, suspect cracked head or even block.

The coolant is obviously being pressurized by combustion process, or the wrong anti freeze has been used at some point, causing a partial blockage in the water ways. If G10 AF is mixed with G12 or vise versa, it forms a gel like substance. Even reverse flushing doesn't always clear it. So you will have to have a pressure test done on the coolant system. If that's OK, suspect cracked head or even block.

As daft as it sounds... Are you sure it's not the thermostat?

Had a stat that had actually destroyed its housing - was fully closed.

Could be causing pressure build up...

I'd have the stat off as a first port of call to see what it's like first, and then probably have each water carrying pipe off, running water through each component to rule it out.

As silly a suggestion as it sounds... If you still suspect a blockage, run the engine with some water in the cooling system at idle, add a couple of scoops of dishwasher powder in with it - it should flush the system right out - drain. If it's really bad stuff coming out, rinse and repeat (sorry for the pun!)

Thanks for the replies.

Had the thermostat off yesterday and its working OK. Tested by hanging in a can of water on a camping stove and it starts opening at about 90C and looks to be fully open by the time its boiling.

While the stat was off shoved a hose pipe into the top hose to the rad and clear water runs out of the hose to the water pump which was also still off. Block and the heater are also clear.

Its running on pure H2O right at the moment (last couple of days only) as weve been getting through that much coolant lately its costing more than the petrol!

I was thinking maybe the heads cracked - pressumably this can only be diagnosed by removing it for pressure testing. Can a cracked head be repaired or is it replacement time? Given the age and condition I think having to replace would be enough to scrap it.

DC

I was thinking maybe the heads cracked - pressumably this can only be diagnosed by removing it for pressure testing. Can a cracked head be repaired or is it replacement time? Given the age and condition I think having to replace would be enough to scrap it.

Yes.

It has to be replaced.

Use a decent S/H head to save a fortune, I wouldn't even bother wasting money on a pressure test, just replace that head.

Yes.

It has to be replaced.

Use a decent S/H head to save a fortune, I wouldn't even bother wasting money on a pressure test, just replace that head.

If you're lucky, people on here may have a spare/old head knocking around...

...I do, but it's 'under surgery' so to speak, and will be going in my car - at which point i'd have a spare - but life keeps getting in the way and the timescales keep slipping.

What head gasket did you use?

And do you remove the thermostat from it's housing to test it? If so was the housing ok?

What head gasket did you use?

And do you remove the thermostat from it's housing to test it? If so was the housing ok?

^^ What he said ^^

Last housing I replaced, I noted that the housing on the inside had disintegrated. Skoda released a 'fixed' version later on that is much better.

Thanks for the replies.

Had the thermostat off yesterday and its working OK. Tested by hanging in a can of water on a camping stove and it starts opening at about 90C and looks to be fully open by the time its boiling.

While the stat was off shoved a hose pipe into the top hose to the rad and clear water runs out of the hose to the water pump which was also still off. Block and the heater are also clear.

Its running on pure H2O right at the moment (last couple of days only) as weve been getting through that much coolant lately its costing more than the petrol!

I was thinking maybe the heads cracked - pressumably this can only be diagnosed by removing it for pressure testing. Can a cracked head be repaired or is it replacement time? Given the age and condition I think having to replace would be enough to scrap it.

DC

It could be a core plug...

It's gonna eventually be a case of having the head off to check it. But if it's going through a lot of coolant it would either be a massive crack in the head, or a core plug.

What other mechanism can be responsible for over-pressurisation of the cooling system causing it to pop a core plug?

I guess it could be a cracked bore, but it's not very likely and it's even harder to test for.

Remember the OP has already fixed the core plug problem which was a symptom of the over-pressurisation, not the cause.

No, it has to be the head casting itself.

Fair point.

Hmmm... Could be air getting in somewhere that is then airlocking the system causing it to pressurise and vent...

Core plug could be down to corrosion, especially if G12 hasn't been used.

Core plug could be down to corrosion, especially if G12 hasn't been used.

What he said.

Go with that.

What head gasket did you use?

And do you remove the thermostat from it's housing to test it? If so was the housing ok?

Head Gasket was genuine part from dealer.

Dont see how you can remove the MPi thermostat from its plastic housing to test it? All seems to be integral and wouldnt want to risk damaging the plaggy clips. The stat is only about 8 months old, as the one in when we got the car had broken from the clips. This was replaced with the genuine part again so should be the updated version.

Definitly not a core plug as the system pressurises and holds pressure, even overnight. No evidence of any external leaks other than the from the bottle overflow and there is no oil in the water or water in the oil.

Is there any history of problems with the wet liners?

Looks like its time for the head to come back off :(

DC

Head Gasket was genuine part from dealer.

Dont see how you can remove the MPi thermostat from its plastic housing to test it? All seems to be integral and wouldnt want to risk damaging the plaggy clips. The stat is only about 8 months old, as the one in when we got the car had broken from the clips. This was replaced with the genuine part again so should be the updated version.

Definitly not a core plug as the system pressurises and holds pressure, even overnight. No evidence of any external leaks other than the from the bottle overflow and there is no oil in the water or water in the oil.

Is there any history of problems with the wet liners?

Looks like its time for the head to come back off :(

DC

There was an uprated head gasket from 'TEMAC' - Should be able to see the logo.

Also...

I've been told rather reliably from a friend that has a felly (which is pretty much the same head) that the torque settings for the head bolts are wayyyyy below what they should be, and should infact be around 50nm for the bolts...

It'd be interesting to hear what other people think on this...?