Thread: TDI COOLING SYSTEM

Originally Posted by discorevy

You might want to test the cap , have you got bubbles in the expansion tank when running? , if it wouldn't normally boil with coolant then it wouldn't normally boil with water if everything is as it should be . obviously the boiling point of water is raised with pressure so if the cap is faulty it can't hold pressure , if your were to drop in to a workshop they could pressure test the cap and do a teekay test at the same time which would answer what you need to know .

The cap has crossed my mind, doesnt seem to be boiling as such and there has been no temp rise. Might just grab a new one any way as mine is probably 9yo.

A good cap must keep constant 1.4 bar in the system where the boiling point is raised to 123*C, it's calculated this way cos the gauge will stay at the middle untill 120*C where it goes up to the next level, the fact that the gauge stays at the middle without being corroborated with a suplimentary temp gauge to see the real temp is not an evidence that everything is OK cos you can run on pure water at 109*C with a good cap without even knowing it(as the electric fan should kick in at 110 to help cooling) and that's not healthy on a long run cos beside the HG it's ''tenderising" the injector seals too... that's why the sensor is fitted there cos the head is sensitive to high temps not the block

IMO using anything else than the recommended 50% OAT mix is not a good move regardless of ambient temps or any other theory

Originally Posted by sierrafery

A good cap must keep constant 1.4 bar in the system where the boiling point is raised to 123*C, it's calculated this way cos the gauge will stay at the middle untill 120*C where it goes up to the next level, the fact that the gauge stays at the middle without being corroborated with a suplimentary temp gauge to see the real temp is not an evidence that everything is OK cos you can run on pure water at 109*C with a good cap without even knowing it(as the electric fan should kick in at 110 to help cooling) and that's not healthy on a long run cos beside the HG it's ''tenderising" the injector seals too... that's why the sensor is fitted there cos the head is sensitive to high temps not the block

IMO using anything else than the recommended 50% OAT mix is not a good move regardless of ambient temps or any other theory

I agree, i had expected to remove the head but its running fine so may be ok with proper coolant mix and a new cap - fingers crossed.

That's all good , but in this case we're not talking about a td5 think the gauge reads different on tdi's and also think cap pressure is around 1.1 bar or so , O.P. was asking if it was OK to run for a short while with weak / no coolant until his problem is diagnosed ( which it is ). Otherwise I'd agree with you wholeheartedly sierra

Originally Posted by discorevy

That's all good , but in this case we're not talking about a td5 think the gauge reads different on tdi's and also think cap pressure is around 1.1 bar or so , O.P. was asking if it was OK to run for a short while with weak / no coolant until his problem is diagnosed ( which it is ). Otherwise I'd agree with you wholeheartedly sierra

...you are right off course, i missread the title and thought it's about Td5, i know noithing about TDIs...sorry

Originally Posted by damienb

Yes, pure water exerts a higher pressure at a given temperature.

I would have thought that a higher pressure at a given temp would make it less likely to boil.

The extreme example of this sort of thing is what would happen to a spacewalking astronaut whose pressurised suit fails.............. his / her blood boils in a very short time, even thought ambient temp might be - 50C.

Also, water boils at lower temps if you go high altitude mountain climbing.

DL

So a change of coolant and new cap and after a couple of weeks its mostly running fine apart from a couple of minor boils in exactly the same place on same bit of road, which is slightly uphill in slow moving traffic on the way home.
Put on a spare viscous unit which also passed the rolled up paper test (as does my original ) i still got a temp rise at the same place.
When i got home last night without any boiling and tested the VC again and couldnt stop it while engine was running, no coolant loss or temp rise but when i loosen the cap i get escaping coolant.

Should i be able to remove the cap without loosing coolant when engine is hot and running or is this a sign of gasket/bolt failure ?
There is no bubbling at all cold or hot.

Opening a hot cooling system cap goes against all common sense. DO NOT OPEN WHEN HOT warning labels feature commonly on these things for a good reason. Coolant WILL be forced out under pressure every time.