Well, the first thing checks the thermostat to see if it opens when it heats or removes it only to try, letting the water flow to the radiator, put a direct temperature pressure gauge to verify that it is not the manometer of your car that gives a bad reading, sometimes it has happened to me that after an engine reheating you kill your head because the temperature does not rise or rise too soon and what happens is that the sensor (pear) is that the sensor (pear) Reheated, that someone has disconnected this, or the cable is peeled and makes dough, or you have the wrong sensor, for example you have connected a bulb sensor in the gauge cable, the direct temperature manometers are cheap and they make them quickly with that you discard that it is not your pressure gauge in case the new manometer indicates that the temperature effectively this bad poor It is in charge of keeping the water passage closed until the engine reaches the appropriate temperature for the proper functioning of the engine. It also verifies that it has adequate oil pressure since it has damage on that side also serious