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Replacing the Radiator Cap

Model: BMW Serie 5 E39 - Years 1995-2003
Part: Radiator

The coolant reservoir also serves as an expansion tank; when the pressure in the radiator exceeds the spring calibration of the cap (the number on the cap represents the calibration value), water escapes through the vent and goes into the tank. When the water in the radiator cools, the vacuum present should draw liquid from the reservoir. Damage to the cap or the thermostat valve beneath the cap could compromise this function and affect the proper operation of the cooling system. Once the engine has cooled, unscrew the reservoir cap and replace it with a new one: in the one shown in the video, the valve has detached from the cap.

Updated on 10 February 2026 by ScegliAuto

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