Engine running cold

my 4.0 never gets really warm. I´ve already changet the T-Stat and the Temp. stays between 65° an 70°C (160°).
But the T-Stat works well in boiling water.
My second thought was the gauge, but if I touch the valve cover it´s not quite hot and the heater blows just slightly warm air, so I think the 70°C on the gauge is right.
What else could be wrong with my XJ?

Try putting a piece of cardboard in front of the radiator and see if the temp comes up. If it doesn't then your gauge or sender is probably hosed. I've seen low temps caused by siezed clutch fan's but the noise is normally the tip off.

If you have an ohmeter, I can look up the specs on the sender so you can see what it is reading.