Preheating indicator

Hello friends, I just joined the forum. My new vehicle I bought a 2012 model bipper tepee does not have a problem in the first start, but the preheating lamp does not go out, but when the engine gets a little warm, it goes out when I turn the ignition off and on. I will be glad if you answer

If the engine temperature does not remain constant, the thermostat can be 70 degrees when I go fast, it drops to 60 degrees.When I go a long way, I squeeze 2 cardboard into the front grille of the vehicle, it goes at 90 degrees normally :)

Welcome aboard. probably the glow plugs or its role may be a problem. If the temperature falls too low while moving, it is a situation with a sliding thermostat.