2a radiator cap issues

Hey guys. So iv got an odd one. Noticed the other day my temp got quite a bit high. Got home to notice steam coming out the front. There's me going oh fish sticks. I let it cool. Take the cap off and it needs topping up. So I thought maybe it just got a bit low as it does sometimes happen with cars and got a bit warm and steam from inside the system came out via the cap. Not Un heard of.

Next day I get to work and the exact same thing happened as I park at work. Steam coming out the front. Turns out to be bits of water around the outside of the radiator boiling to steam. So I think weird. Squeezed the top pipe to feel for pressure and as I squeeze I can hear air coming out from the overflow pipe just under the cap. So what it sounds like is the cap not making a pressure tight seal. No pressure in the system meaning it's getting hotter than it should be if my understanding is correct (that the pressurisation of the system helps stop the water from getting too hot) please correct me if I'm wrong here by the way.

Anyhoo my obvious next reaction is to check the filler cap. Maybe it's gone? Well I know the cap isn't very old. Less than a year. And looking at the seal, I cannot see any wear of tear etc. Same can be said for the filler neck. Looks fine. And the spring for the cap is good too.

So basically I need someone to explain to me what sorcery is at hand here? I don't mind buying a new cap as they aren't that expensive but I'm puzzled by the fact I can't see anything wrong with the less than a year old one.

And I really do not wish to buy a new radiator after seeing how much they are.

By the way. On mine the overflow pipe has snapped off. Are the filler neck repairs that you weld on worth my time?

Aaaaaaaand.......

How hard is it to get out a sheared off thermostat housing bolt? Before anyone says it. Yes it does leak from there due to the third bolt not making a seal, however due to my prior knowledge of this iv kept my eye on it for some time now and can say that it barelyG

Do you have the correct pressure cap? Maybe get one of each pressure and see which is happier. A cap can often look fine but behave as yours is - at least they're cheap. I assume your stud is broken off flush? If not can you get it with mole grips? Good luck

Is this one of the caps that has two seals?

If so, one breaks under pressure, and the fluid goes to the overflow. But then, when it cools, the other breaks, so it can be sucked back in (due to the vacuum created when the engine cools)

Horrible system, imho, but that's the way it is.

You need to find a cap of the right physical design, and then with the right 'pounds' pressure rating on the spring. Its not too hard to find one, but you just need to be sure the numbers are right.

Just your average cap. One rubber ring under a strong spring. Will go to halfrauds in the morning

Why are you buying from Halfords? They will not sell the correct cap. Try online at Craddock's they sell them for about a fiver.

I hope you aren't in a hurry if you order from Craddocks. I've placed 2 orders with them in the past couple of months, first order took 3 weeks! and I am on week 2 of the second order may be getting close to week 3 now.

Stormintrooper said:

No pressure in the system meaning it's getting hotter than it should be if my understanding is correct (that the pressurisation of the system helps stop the water from getting too hot) please correct me if I'm wrong here by the way.

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pressure increases the boiling point. doesn't make a difference to the temperature of the fluid. if you don't have pressure or antifreeze (which also raises the boiling point) then you'd get localised boiling and evaporation (steam)

I know I keep praising Famous four BUT they never fail...delivery quite often next day! Not weeks
Also
Always have or can get required part
And
Knowledgeable and helpful

LordOWar said:

I hope you aren't in a hurry if you order from Craddocks. I've placed 2 orders with them in the past couple of months, first order took 3 weeks! and I am on week 2 of the second order may be getting close to week 3 now.

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I got one from car spares ltd in the end as a temporary fix. I'm fairly certain my thermostat isn't always opening because on the odd occasion after a few bumps in the road I see the needle drop back down to normal

Got a few bits and bobs on the way from paddock. Cap. Thermostat. Overflow pipe. Speak g of which. Does the expansion bottles lid need to make a tight seal or just enough to stop fluid sloshing out?