Mercedes S-Class W-140

1. Before removing and checking operability of the thermostat, be convinced that problems with cooling of the engine arose not owing to insufficient amount of cooling liquid or a weak tension of a driving belt. Be convinced of serviceability of the indicator located on the control panel.
2. If you noticed that the engine long gets warm up to the working temperature (according to indications of the indicator), the thermostat, perhaps, is jammed in open situation. In this case the thermostat should be replaced.
3. On the other hand, long warming up can be a consequence of lack of the thermostat. It could be made specially or inadvertently (forgot to establish after repair). Do not use the car without thermostat. The control system of the engine will keep the engine in the warming up mode longer time. During this time the engine will consume bigger amount of fuel, and the fulfilled gases will contain bigger amount of harmful impurity.
4. If the engine overheats, touch the top hose of a radiator. If it not hot, but the engine is overheated, the thermostat, perhaps, jammed in a closed position. Liquid does not get to a radiator and circulates on a small circle. In this case replace the thermostat.
5. If the top hose of a radiator hot, it means that the thermostat is open and liquid normally circulates on system. In this case study the recommendations provided in Diagnostics of malfunctionsthe Section Introductions.