Radiator Cap changed level went up?

[Buddy]

In my experience this has never been seen before...

The car has been running normally ever since I change the thermostat unit a year ago, around a month ago I found that the radiator cap wouldn't unscrew until I warmed it up for a few minutes and then it would unscrew, so one to be changed at some point, the level had dropped a few millimetres and so I ordered a new cap and it came, fitted it this afternoon took it for short run about five miles and returned home everything seemed normal until I opened the bonnet and I saw the coolant level was just below the cap, so it's cooling off and I will change the cap for the old one and take a short run. Does anyone have any ideas what could be wrong with the cap? First thought is that it's not made correctly for the pressure release so low pressure and the level will rise, duff cap.

 

[lfe]

If the cap is defective, it may not hold pressure and steam bubbles may form, causing the level to rise.

The pressure causes the refrigerant to boil at a higher temperature.

It is the center of the cap that makes the seal, check that it has the O-ring.

 

[Buddy]

I compared the two caps old and new for the height compared to the outer rim and the new one was about three mm less than the old item, maybe because it has a lower pressure setting, refitted the old item and drove it the same distance as yesterday the level remained where it was when I set off. So the problem is with the new cap, I'll look for the O ring thanks. For info this item was a brand called ROBUST sold on Amazon.

 

[lfe]

I bought this one last year and it works well, for the THP engine

febi bilstein 37600 Radiator Cap for coolant expansion tank, pack of one,grey|black : Amazon.co.uk: Automotive

febi bilstein 37600 Radiator Cap for coolant expansion tank, pack of one,grey|black : Amazon.co.uk: Automotive

www.amazon.co.uk