Some drivers check out the fluids, but they get it wrong most of the time when they do it. For this reason, the radiator cap is made of a special 2-way valve that releases the pressure to the expansion tank. By nature, as the pressure is being released towards the expansion tank some coolant escapes with it to the expansion tank. This increases the level of the coolant in the expansion tank and reduces the same amount in the engine block. The most critical part about reading the automatic transmission is, unlike all other lubricating systems in the car, most car manufactures service manuals indicate that the reading should be taken while the car is running.

Source: The Star February 25, 2021 11:01 UTC