Actually the 140 on the cap means 1.4bar or about 20psi. Some caps say 120 and that means 1.2 bar or about 17psi.

Haven't seen any 100 caps in about 20 years. That would be about 14.2psi.

Lower the level in the reservoir and see if there is pressure after it is cold. There should be a small gaseous pocket above the coolant in the reservoir even when hot. If the tank is full cold it will presurize just from thermal expansion as it heats.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician