Mercedes-Benz W124 coolant loss – where to find the leak
Mercedes-Benz W124 is losing coolant but no leak is visible – where could it be leaking?
Common places are the expansion tank cap, the top and bottom of the radiator, hose clamps, the block heater O-ring, the heater pipe O-ring and the water pump seal. The leak often shows only when the engine is warm and under pressure.
How do you locate a coolant leak in a Mercedes-Benz W124?
Check the engine warm and running, also from underneath. A water pump leak shows from the hole at the base of the pump. Coolant can run along structures far from the leak point, so dry the areas and follow where the wetness starts. A small crack in the thermostat housing also leaks only when warm.
Can the expansion tank cap cause coolant loss or temperature fluctuation?
Yes. The rubber seal and spring of the cap wear, so the pressure drops and coolant escapes or boils too early. The number on the cap tells the pressure, for example 140 means 1.4 bar. Replacing the cap is cheap and worth trying first.
How can you tell that the head gasket has leaked?
Signs are foam or grey oil under the oil filler cap, pressure in the cooling system, bubbling coolant and white smoke from the exhaust. A workshop can confirm it by measuring exhaust gases in the coolant.