When removing the radiator cap after not driving the car for 2 weeks it is like opening a can of coke it is still holding pressure, stuffed cap ? Suggestions ?

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That's why it's good to be.............ME

Is it definitely high pressure escaping when you open it or possibly low pressure drawing air in?

If you have an overflow with a return-type cap, it could be that the heat is forcing the water out, but when it cools the water is not allowed to be drawn back in again, creating the relative vacuum. From maybe an incorrect cap or a knackered cap?

I just wouldn't expect it to be HIGH pressure, as even if it got hot and created high pressure, cooling would return pressure to normal. If the high pressure let water out when hot, you'd actually expect it to be in relative vacuum when it cool if if doesn't have a coolant overflow/return reservoir and cap.

But that's just my initial thoughts, let's see what others think.

Either way, I'd replace the cap and see how it goes. They're pretty cheap.

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

If you do replace it make sure you get one of the correct length. I once drove a Mini for the first time and wondered why it was overheating badly. Turns out it had just been fitted with a short neck cap instead of long so the sealing rubber ring on the cap didn't reach to the mating surface in the radiator neck. Hot water was simply gurgling out the overflow tube.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

If renewing, measure the depth to the sealing lip that the cap sits against.

Tridon spec sheets recommend CN1390 which in my experience is too shallow and incorrect length @ 31mm. I use Tridon CR1390 @ 34.5mm depth. [1390 = 13Psi/90kPa]

CA1390 is also too shallow; CB & CC are small connection bayonet type.

F

No overflow and definitely pressure out it is a 50 mm alloy radiator.

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That's why it's good to be.............ME

Not something weird like head gasket leaking combustion pressure in the coolant passageway? That's probably a stretch...

Sent from my Pixel 2 XL using Tapatalk

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

I would like to think not , pump , radiator, head gasket , hoses etc all replaced about a year ago.

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That's why it's good to be.............ME

I am having the same issue with my 50mm radiator,
It does not suck the water back in when its cool and the radiator it self still holds pressure.
I purchased a new cap and hoping it will fix it all.

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http://www.flickr.com/by_dan
Current: 1970 Mini K 2014 Focus ST
Past: 93 Rover, 64 850, 97 Rover, 66 Deluxe, 66 Moke
81 Austin Estate, 2006 R53MCS, 66 Deluxe, 1978 Clubbie
2014 Land Rover Defender 90

Have you got a regular cap or a "recovery type" cap? The regular caps will push out coolant and it air takes it's place. The recovery ones will allow coolant from the reservoir to be sucked back in

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Recovery, Has the 2 seals.
Maybe its an excuse for me to do an engine rebuild.

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http://www.flickr.com/by_dan
Current: 1970 Mini K 2014 Focus ST
Past: 93 Rover, 64 850, 97 Rover, 66 Deluxe, 66 Moke
81 Austin Estate, 2006 R53MCS, 66 Deluxe, 1978 Clubbie
2014 Land Rover Defender 90