Radiator expansion tank cap - replacement for 3M5H-8100-AD

Radiator expansion tank cap

The expansion tank cap is an unassuming but very important part of the engine cooling system. Its job is to seal the coolant tank tightly and maintain the proper pressure in it. It works like a two-way valve - it releases excess pressure at high engine operating temperature and at the same time equalizes pressure as the system cools down, so the radiator works properly and the coolant does not boil prematurely.

When to replace the cap

Typical symptoms of a worn or damaged cap are a low coolant level despite no visible leak, air getting into the cooling system, the expansion tank overflowing and a tendency for the engine to overheat, especially in traffic jams or on long drives. Replacing the cap with a new, correctly fitting part eliminates these problems and restores proper pressure in the system.

Fit and installation

The product is a replacement marked with OEM number 3M5H-8100-AD and fits selected Ford models, including C-MAX, Escape, Fiesta and Focus in the listed production years. Installation is very simple - once the engine has cooled, just unscrew the old, worn cap and screw the new one in its place, with no need for specialist tools.

Material and construction

The cap is made of durable ABS plastic resistant to high temperature and contact with coolant. The twist-on closure ensures a tight seal and secure closing of the tank, and the low weight and compact dimensions do not burden the system.

Specifications