2002 Jeep Liberty running hot, help!

We bought a 2002 jeep liberty about a month ago. Come to find out, there was little water in it and it ran hot one night on my way home to work. Well I put water in it and now it ran fine until the g/f said it ran hot on her way to work. We still have warranty, and am calling the dealership tomorrow, but if there is a leak, my luck they won't find it. THIS IS DRIVING ME NUTS! Anyway to tell if there is a leak? I havent put water in it yet but if it did run out im sure it is low. Would the leak be the only reason? I changed the oil after the night it ran hot. Any tips will help

It took over a gallon to refill the radiator and resevior. ANY idea's on how to find leaks? I dont want to put out 40 if they won't find anything

First of all, if it's losing coolant make sure to keep the level up, or you'll have othe problems.

Does the water level get low quickly? Let it idle in your driveway for awhile, when it's getting good and hot. Check for leaks. Check the exhaust also, if it's very wet/steamy then you may have a head gasket problem(and if so, check the oil also as it can be fouled by the water)

A little more info would be helpful. How long/how many miles between it getting hot/running out of water? How many miles on the vehicle? See any steam coming out from under the hood at traffic lights? Does the cooling fan(s) come on?

Sorry for the late response, I don't get to the Liberty section often, but will try to do so now!!