The indicated altitude shown on the altimeter will not change when Outside Air Temperature changes.
The altimeter is calibrated for ISA conditions, and only in these conditions will the indicated altitude and true altitude be the same.
When below ISA conditions, the altimeter will over-read, meaning that the indicated altitude will be higher than the true altitude, which is dangerous because it places you closer to the ground for the same indicated altitude.
When above ISA conditions, the altimeter will under-read, meaning that the indicated altitude will be lower than the true altitude. This can be a problem when flying approaches using VNAV in hot summer weather as you will arrive on a higher descent angle than normal.
When sitting on the ground above sea level (a constant true altitude), and with changing temperature, the altimeter reading should vary and the indicated altitude should increase with decreasing temperatures (over-read), or decrease with increasing temperature (under-read).
To get the true altitude from the indicated altitude, the following formula can be used :
True altitude = Indicated altitude + 4 x (Indicated altitude / 1000) x delta ISA ; where delta ISA is ISA deviation in °C and altitudes are in ft.
Three screenshots showing no effect of temperature on the altimeter :
ISA conditions :
ISA - 20°C :
ISA +20°C :
