If you have the owner manual for your car you will find that the light may "flicker" at times on idle if the engine is warmed up and you're either stuck at a long red light or stuck in traffic and cars are not moving or moving slowly. The same is true on Henry J automobiles. If the temperature gage is working and it does not start going up, don't worry about it if it goes out with higher revs. It's a reflection of sender calibration.