In the case of the arrow in the forbidden sector you are dealing with the closing of the thermostat, when the coolant is forced to circulate in a small circle. The engine is overheating from the fact that the main part of the heat remains in the engine. In the second case, you see the opposite pattern. Because of the constantly closed thermostat the engine on the contrary is not enough heat and therefore you face excessive fuel consumption. A faulty thermostat will have to be removed, but only after flushed coolant.
Now you need to remove dirt, scum and bring order to the hole in the valve. But before that, check the thermostat. To do this, put it in a saucepan with the water and start to heat on the tile, after having prepared a thermometer with a scale, designed for temperatures in excess of 100градусов C. during the test, you need to fix the temperature at which the valve opens, and what is the resulting hole size. You should pay attention to the temperature marked on the valve body of the thermostat. From Vazov she is usually 81-85 degrees, and some cars – 92-93 degrees.
There is another type of check of the thermostat – the size depending on the degree of heating. To do this, you should be armed with Vernier caliper and measure the distance between points in a cooled and heated state. The difference during the measurement, generally at least 7 mm.
Wait until the thermostat has cooled, and check to see if the valve closed completely. If you find that the thermostat is malfunctioning, do not attempt to fix it, and go to the nearest auto parts store and buy a new one.
If the store will not the thermostat for your car, then you know that you can do without it. Take a piece of thin plastic cut from a circle and make a few holes, then put this simple device in place of the thermostat. As a result, the circulation in a large circle will be difficult and will resume the flow of warm water into the heating compartment, and to ensure that the operating temperature of the engine.