Hi Amarin,

Yesterday I got the new green cap for the expansion tank, so I removed the old grey one and replaced with the green cap (Volvo and both of them 150 kPa).

The engine was cold, so this morning I drove about 15Km and then parked the car back in my garage.

I checked all the hoses to the radiator, no leaks, but the level of the fluid went to the min.

This evening, after 8h the car was unused, I checked again, no leaks from the radiator hoses, however I have noticed some liquid leak from the tank, specifically from the small hose that goes to the radiator. No leak from the hose under the tank.

However, the shape of the tank itself (the side that looks at the exhaust manifold) has changed from flat to be slightly curved (like, a small belly), which has led me to think that the pressure was very high.

I started to slowly undo the cap, man the water from the min. level overflew and the pressure was huge indeed. I closed again and did the process again until the pressure was gone.

I do not know what to think at this point, but such a high pressure to warp the tank after 8h the car is unused, it is not normal.
With the old grey cap, I had leaks at the radiator hoses, and did not warp the tank.

What can generate such an anomaly?

Alessandro