Good working thermostats are critical to proper engine operation. This is true on both gasoline and diesel engines. The engine needs to warm up quickly and stay hot during operation to reduce internal engine wear. I thought you just had to see the last one I pulled out of a Mercedes engine. Talk about failure! I had a customer come in recently with a small leak in his radiator hose. He said the engine got hot but did not overheat. He also complained that after the incident the heater was not working very well.
Problem & Solution
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I thought to myself right away that he probably fried his thermostat. I replaced the hose and removed the thermostat housing. Sure enough the thermostat came out in pieces. This type of severe failure is not all that common but this is not the first time I have seen a thermostat go bad when the engine got hot. Anytime your engine gets hot from loss of coolant just replace the thermostat! Also, keep in mind that thermostats do not last forever. After only a couple years they can become sluggish and prevent your engine from running at peak performance. Remember - your diesel engine needs to be running at proper operating temperature for the diesel fuel to burn properly. Also, if the heater is taking a long time to warm up the car then consider replacing the thermostat. It is cheap!