Light Liquid Level Refrig

hello!.
The temperature needle is stable rises normal when the engine is heated.
When I start the hot engine (with the needle outside the heating area) the little look does not turn on and works normally.
If I start with the needle inside the heating zone, the light turns on but less time. It is not always at the same temperature level.
I am thinking of changing the expansion tank and the thermosensors have passed. I imagine that it will not be very expensive like this I am checking where it is from?

hello!.
The temperature needle is stable rises normal when the engine is heated.
When I start the hot engine (with the needle outside the heating area) the little look does not turn on and works normally.
If I start with the needle inside the heating zone, the light turns on but less time. It is not always at the same temperature level.
I am thinking of changing the expansion tank and the thermosensors have passed. I imagine that it will not be very expensive like this I am checking where it is from?