Water temp problem

The antfreeze in my 94 cherokee never gets hot it is always super cold and i have replaced the thermostat and the radiator cap!!! Any ideas???

Maybe a bubble in the system. make the radiator cap the highest point in the engine(IE wheel ramps or jack stands) and take the cap off and let the engine run and keep it topped off...let her bubble. Thats all i can think of right now.

-PJ-

Probably not a problem, but give us more specifics. Where are you and what are the air temps? Start up, drive around easy for 10-15 minutes, what's the reading on the temp gage? Then come home (or somewhere you can sit a while) and let it sit and idle for 10-15 minutes - now what's the reading on the gage? Have you got any nice long hills handy, especially a gravel or dirt road? Drive up and down and then back up the hill, slowly. What's the temp gage read now?

A couple other general points:
Air bubble in the system usually leads to overheating, not underheating.
Quite a few people have found their temp gages to be faulty - do you have access to a direct temp probe you can put n the engine to get another temp reading?
You can check the thermostat operation relative to your gage by (starting from cold) let the jeep idle and keep your hand on the upper radiator hose. When you feel it start to get warm, it means the thermostat has opened - go look at the temp gage reading.

Your 4.0 should be in the 200-210 degree range once the stat opens. Post your reading.

Aside from the gage reading, do the hoses (or the motor even) get hot? If not it's the thermostat. If they do get hot, it's the gage or sending unit.

i dont even have a temp gauge on the jeep but i dr it for an hour straight yesterday and popped the radiator cap and the coolant was still cold!

Most likely, the thermostat is no good or in backwards.

If it was in backwards, the heat sensing pellet would always be on the cold side and would never open. This or a bad thermostat never opening could fry your motor from overheating without the coolant getting hot. If you pull the dipstick, can you hold the oily end or is it too hot. Does the motor crackle when you turn it off? Does the head feel extermely hot. Be careful of the exhaust manifold, no matter what, it will be hot.
If the motor is very hot, you are in extreme risk of ruining it. Usually you warp the head and blow the gasket. Things other than a thermostat, like a bad water pump or some other blockage of coolant flow could cause this same condition.

If both the motor and the coolant are both cool, the thermostat is stuck open. Pull it out and test it in a pan of hot water. You could also try blocking off the radiator with cardboard and see if the coolant gets hotter.

Obviously, driving without a temperature gage is risky. So try to determine if both your coolant in the radiator and your engine is cold, or if your engine is hot, but your coolant is cold. If the engine is hot and the coolant is cold - don't run it until you get it fixed.