No coolant pressure

The coolant system on my 20VT doesn't seem to be pressurising, even when red hot - I can remover the cap with no pressure release at all

The strange thing is the system is behaving as it should - warms up, sits at 84-86 degrees cruising & the fan cuts in at 96 degrees or whatever it is. I have changed the coolant & bled the system twice.

Obviously I suspected the Expansion tank cap, but there is no evidence of any hot coolant escape from the cap at all. Would it be worth replacing it anyway?

The radiator is getting tired (going to replace in next few weeks) but no serious coolant loss.

Anyone else had this? - is the car ok to drive with no pressure in coolant system? or is this normal

Thanks in advance

If there's no pressure in the coolant, it will boil at 100C instead of the 112C or so it's intended to boil at... below that temperature it will be fine - the system isn't designed ever to get that hot - but it'll be close to or over normal boiling point in a traffic jam on a hot day, or after a spirited run.

The likeliest culprit is the cap, but the question is: does the level in the coolant header get lower? If it does, that's almost certainly where it's going.

However, you do mention that the radiator is tired and has 'no serious coolant loss'. It doesn't take much of a leak - almost certainly invisible - to start losing water and therefore hot pressure. Might be worth pressure testing the whole cooling system.

Running with a leaky system will - depending where the leak is - tend to cause any excess fluid to leak out so that the system is 'just full' when its at normal running temperatures. You'll lose a little more each time... I'd be looking very carefully at the levels and temperatures if it were me as a hot alloy head can distort.

Thanks, yes I have no discovered the Rad IS leaking, down the R/H side as you look at it, on the Engine side. Surprised really as it's only done around 10'000 miles since brand new (over a few years!) & it wasn't a cheap one. Looking to order a new one now

Just ordered the alloy one off the 'Bay, had a Valeo fitted a few years back now and it is on it's way out. I did hear that some don't like the alloy rad as it does not 'flex' like the Valeo etc and therefore splits....don't know how true that is or whether I heard it correctly but given the lack of OE rads at anywhere near sane prices I have gone for the alloy one.