Hey I have a '91 YJ with an 4.0...just rebiult the engine and everything works fine but the temperature never passes 55 celcius. It was at 98 degrees for the first 7 years i've owened it. Thermostat is fine and I know the temperture gauge works because after 1/2 hour of running i can put my face on the valve cover. It's the strangest thing I've ever seen......anyone out there know of anything like that happening before??

 

Are you sure the thermostat isn't in upside down.

Cheers,

 

its a good thing, what is the size of radiator?

 

Check this first... then if there is a bypass hole in thermostat.. like a thermo protection hole (allowing coolant through).. you jus may have a good situation there. **** your wife off, and grab a thermometer from the house. WITH ENGINE COLD (sorry for caps... people do silly things someimes) start engine, and run it. Confirm your gauges aren't off. Check and see if your clutch fan hasn't welded itself together. Make sure you have the right water pump on it. Such as clockwise or counterclockwise rotation, this can lead to explosive things, and low coolant readings. GLuck