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 a control panel.
2. If you noticed that the engine long gets warm to working temperature (according to indicator indications), the thermostat, possibly, is jammed in open situation. In this case it is necessary to replace the thermostat.
3. On the other hand, long warming up can be a consequence of lack of the thermostat. It could make specially or inadvertently (forgot to establish after repair). Do not use the car without the thermostat. The control system of the engine will keep the engine in a 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 перегрет, the thermostat, probably, 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 familiarize with the recommendations provided in the section Diagnostics of malfunctions of Introduction.