Why Do They Fail?

Expansion tanks are continually exposed to heat, pressure and coolant and can fail over time due to:

• Plastic becoming brittle through repeated heating and cooling cycles
• Hairline cracks developing in the tank body
• Cracks or damage around hose connections and mounting points
• Seal deterioration around integrated sensors and fittings
• Coolant contamination or incorrect coolant attacking internal surfaces
• Excessive cooling system pressure caused by another system fault
• Physical damage during servicing or component removal
• Expansion tank cap faults allowing incorrect system pressure

Symptoms of a Failing Expansion Tank

• Visible coolant leaks around the tank or hose connections
• Unexplained or recurring coolant loss
• Low coolant warning messages
• Visible cracks, staining or discolouration around the tank
• Coolant smell from the engine bay
• Wet areas or dried coolant residue around seams and connections
• Engine temperature running higher than normal
• Overheating if sufficient coolant is lost

Because small cracks can open only when the cooling system becomes hot and pressurised, an expansion tank leak may not always be obvious when the engine is cold.

Fitting Tips

• Allow the engine and cooling system to cool completely before removing the expansion tank or cap
• Identify the cause of the original failure before installing the replacement
• Inspect all connecting hoses, clips and fittings for deterioration or damage
• Replace seals and O-rings where required
• Check the expansion tank cap and replace it if its condition or operation is in doubt
• Transfer coolant level sensors carefully where they are not supplied with the replacement tank
• Use the correct manufacturer-specified coolant type and concentration
• Refill and bleed the cooling system according to the vehicle manufacturer’s procedure
• Check carefully for leaks once the engine reaches normal operating temperature