Motor temperature does not rise.

Hello, I have a Mercedes Vito del 97 that I just bought second -hand. I am observing that the temperature needle rises very little from 40 to 60 degrees on the highway. If you go up when I start with slopes and others that passes from 80 degrees to 100 grades.
Does anyone know if this is normal? Because I think it should be kept above 80 degrees even on a normal walk.
And what could be the cause?
THANK YOU.

Verify if you have the thermostat, or if you have it not open.

Hello, I am almost sure that the car has taken away the thermostat of AHI that the more refrigeration is down the coolant temperature