Is it normal in a cold car (off for many hours) for the coolant level to rise slightly into the coolant reservoir when the radiator cap is removed? It rose maybe 1/4 of an inch but I thought there is supposed to be no pressure when a car is off and cold car.
If there’s even slight pressure this is what I’d expect to happen. Is this a pressurized coolant reservoir when the engine is hot?
Probably. If the reservoir was vented all the time, the level in there could vary any time, not just when the system was depressurized.
My WAG, when cap is opened, hoses slight contract raising the coolant level in the reservoir l