Temperature gauge ALWAYS stuck at bottom of cold.
 

When I turn on my saab 900s 2.5 v6 the temperature on the gauge moves up slightly to the bottom of the cold position. But no matter how hot the engine gets throughout the course of driving the needle will not move. I have had the check engine light come on but only a few times of the past few weeks.

I replaced the temperature sensor because this was easy to do and there was no change. I havent yet changed the thermostat because this is a big job with this engine. But the heater works fine and I would expect atleast a minor rise in temperature even if the thermostat was stuck open.

What advice does anyone have for this? am I wrong with the thermostat not being able to cool that efficiently? Yes I have heard that the ecu will set the temperature to zero if it thinks its wrong. But surely there has got to be minor variations if the temperature sensor system is working correctly.

Is the thermostat really a big job on the V6? It's usually very easy, but I never did one on a V6. It's most likely stuck open.

Its not in the most ideal spot. Need to remove belts to get at it. Would the running cold affect the power output? Its done 250,000 km but since roughly 245k the economy has dropped from 9l/100k to about 10.4l/100k despite having it serviced in that time. Also it doesnt feel as powerful as when I got it. Find myself chopping down to 4th gear to overtake and go up steep hills. 5th gear never used to phase it.

Thanks for the advice anywho.

Yes, running cold will affect both power and fuel economy not in a good way. It can also have ill long term effects.