Coolant leak: causes, risks and affected cars

A falling coolant level means a leak. It can be visible (puddle, traces under the engine) or internal, when coolant gets into the engine and burns. Either way, a loss of coolant must be dealt with quickly to avoid overheating and head gasket damage (Fiches-auto, Audi A4).

The most common causes

The water pump

This is the most cited cause. On recent engines, its plastic housing can crack, as on third-generation EA888 engines from the Volkswagen group (GetCarwise, Audi TT). On the Audi Q3 1.5 TFSI, water pump failures are reported between 30,000 and 60,000 km (CarVerif). Caradisiac also notes water pump leaks on the Alfa Romeo Giulietta (Caradisiac).

Plastic hoses and pipes

On the Audi A6 3.0 TDI, fragile plastic hoses split from 80,000 to 120,000 km, for a repair of €400 to €900 (CarVerif). On the BMW X5 V8, the plastic coolant pipes under the intake fail without warning and can only be reached after major dismantling (GetCarwise).

Radiator, expansion tank, coolers

On the Chevrolet Trax 1.4 Turbo, diagnostic sources cite the radiator, expansion tank, hoses and water pump (GoodMecano). On diesels, the EGR cooler can also leak: see white smoke.

Cylinder head or head gasket

An internal leak, with no visible trace, points to the cylinder head or its gasket. The 2.0 TDI 140 of 2004 and 2005 Audi A3s is known for cylinder head problems (Fiches-auto). Pressure in the system, bubbles in the tank or white smoke are the signs (Fiches-auto, Ford Kuga 2).

What to do

Check the level with the engine cold and do not drive with the level below minimum. Opening the expansion tank with a hot engine is dangerous: wait for it to cool (Caradisiac). If the temperature light comes on, stop: see temperature warning light and overheating.

Before buying a used car

Check the expansion tank level with the engine cold, and look for traces under the car and under the bonnet. Falling coolant, bubbles or pressure rule out a worry-free purchase (CarVerif, Ford Fiesta). Ask for water pump invoices.