lower radiator hose
I'm guessing, but the coolant level sensor is probably in the overflow bottle and it is low. This is so you notice it before the radiator itself is low.
Because most if not all vauxhall engines are air cooled, hence when you are driving the temp comes down
Remove the bottom radiator hose. Stick a hose in the top of the radiator. Turn the water on. Allow the water to run through the radiator and out the bottom of the radiator.
unplug line at bottom of overflow or bottom of radiator
Remove the bottom radiator hose on your 1996 Chevy Lumina radiator. Put a water hose in the top of the radiator. Allow the water hose to run until the water draining from the bottom of the radiator runs clear.
The water pump on a Vectra 2.0 DTL is located just behind and to the right of the crankshaft pulley. This is on the front of the motor. One easy way to find a water pump is to trace where the hoses go from the radiator.
check around the small rear windows, bath sealant can help.
from the top to the bottom
When the thermostat is open the coolant will flow through the top radiator hose in to the radiator and out to the water pump through the bottom radiator hose
Remove the bottom radiator hose from your 1995 Chevy Lumina radiator. Put a water hose in the top of the radiator. Allow the water hose to run. Keep the water running until clear water runs out of the bottom of the radiator.
Try the rear side of the radiator approx. 1/3 down from the top
Remove the coolant from your 1997 Chevy Malibu radiator. Remove the bottom radiator hose. Run water through the top of the radiator allowing it to run out the bottom.