May 25

Mercedes Thermostat Replacement

Auto Repair, Car Costs, Car Maintenance


We recently serviced a 2006 Mercedes C280 with a check engine lamp concern. Although the vehicle drove fine there was a trouble code indicating the engine was not warming up properly. Modern cars have fabulous monitoring of engine, emission and fuel systems and can tell us many things that are not operating properly.

On this vehicle the concern while driving was barely noted: heat in the cabin was good and the temperature gauge read a warm engine. With the scan tool connected I did see that the engine was in fact not reaching operating temperature. After confirming that the sensor was reading correctly, I proceeded to remove the thermostat for inspection and there the cause was found. The thermostat was stuck slightly open as shown in the photo. It’s just a millimeter but this makes a huge difference.

A thermostat should remain fully closed until the engine coolant reaches a high temperature, around 85C when it opens and allows flow to the radiator.
The reason the Mercedes (and most other vehicle’s) engine diagnostic system monitors coolant warm up is because it is critical for an engine to warm up to proper operating temperature quickly. Once proper operating temperature is reached, combustion efficiency is maximized, pollutants are minimized and fuel mileage is maximized.

Once this repair was completed the engine warmed up quickly to proper operating temperature. A benefit to our client is that she will save money on fuel, which helps to offset the cost of repairs.

Mercedes Thermostat Replacement
new thermostat on left, defective thermostat on right: note the 'gap' at the arrowhead

About the author 

Bernie Pawlik

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