Depends on what the radiator cap is set to release at. I run a 1.3bar in my car so that equals to around 19psi release. Generally it stays under that unless the coolant temperatures really start to skyrocket. The factory cap is 0.9bar so about 13-14psi. Unless you drive the car extremely hard, the pressure should stay around like 10psi or so. Just a rough estimate. If anyone else knows for sure then please chime in!