I have a 1996 Jeep Cherokee Sport 6 Cylinder.(140,000 miles).
Regarding the symptoms my Jeep is experiencing: Overheating and loss of coolant (not spilling on ground but disappearing mysteriously out of the plastic resovoir), and Temperature Gauge rising quickly past 210-260 as soon as car begins to move… After asking
around and going through the process of elimination with a few people willing to share info without holding my car hostage;) for expensive repair I might not need (it’s happened before-I’ve been an easy mark;)…I determined there is no coolant mixed with the oil.YEA!!! Rather than get all freaked out and fall into a trap of thinking I need a whole new radiator and a water pump and new fan assembly etc., (all hoses seem fine,can I just replace the Thermostat and see if that solves the problem? Overheating is the only real problem this car has had since it was driven off the showroom floor. My teenage son had it for a few years and did not maintain it well.I have been ‘backing-up’ trying to improve the condition of the car ever since…it’s a great car and still in very good shape otherwise. I have spoken to 2 ‘independent’ master? mechanics in my neighborhood and the hairs on the back of my neck stood up 
I am somewhat mechanica-if I knew exactly what tools to use and was given precise instructions I might be able to figure out how to replace the Thermostat myself. At this point it is a necessity. Also, I don’t know exactly what Thermostat I need and to know if I am being gauged on the price.
Thank you for your support,
BuggyBumpers
Dear buggy a thermostat is easy but that would not account for coolant loss, I am afraid you may be looking at a blown gasket, that will be a few hundred dollars. It is a great fun toy, but you can have a compression check done, and a pressure test on the coolant system, but I think you have a major medical type repair to fix the problem.
You can try the thermostat.
Open the hood and follow the upper radiator hose to the engine to the thermostat housing. Two bolts hold the thermostat housing to the front of the engine. Do you think you can remove and reinstall these two bolts? If so, go to the parts store and get a thermostat and a gasket.
Tester
Changing the thermostat is a long-shot but it’s worth a try. Follow the upper radiator hose to where it connects to the engine. Inside that housing resides the thermostat. The housing usually is secured with 2 nuts or bolts with 1/2 inch or 9/16 inch heads. Before you remove them, you should have a new thermostat and gasket in hand. You will also need a gallon of anti-freeze, 50-50 mix. The “green” kind.
Remove the fasteners from the housing (you can leave the radiator hose connected) and gently ply it off the engine. Remove the radiator cap before doing this, a small amount of anti-freeze will spill out when you remove the housing…The thermostat will be either in the housing or in the engine block. Observe how it is positioned, remove it, and clean up the mating surfaces with a scraper. Install the new thermostat. Make sure it rests in its groove. Install the gasket. Install the housing. Refill the cooling system and replace the cap. You are done.
If this does not cure the problem, have the cooling system pressure tested which will expose any leaks. They can also check for a head gasket problem at this time. If that checks out, the next suspect is the radiator. With age and mileage, they can get plugged up and in high salt areas, the fins can be corroded right off the tubes, rendering the radiator useless…
Is it possible that steam or water boiling out of the reservoir could account for the water loss you are experiencing? Based on what you have told us, I think that the thermostat is a pretty good bet.
A thermostat for this car is $5, so it is certainly a good idea to toss one in and see if it helps. $5 buys you about 3 minutes of a mechanic’s time.
You guys are angels!!! These reply’s have provided some serious relief as I step into the ‘unknown’ of automotive repair. By sharing this info you have not only provided easily understood instructions, but bolstered my confidence in troubleshooting my Jeep’s cooling system issues. I will keep you posted as I follow these instructions. Oh, yeah, would it be better for me to go to Parts Dept. of Jeep dealership for Thermostat or will any part store work. Is a 'universal part just as good as a Jeep part as far as proper fitting is concerned? Also, The Radiator is not the original and was replaced in the last 5 years. Thank you so much for your support.
The thermostat that came in the car was made by Gates, so if the one you find at the auto parts store or on-line is a Gates, you can have the confidence that you are using original equipment. Or you can go to the dealer and spend twice as much, but it is still not a lot of money. Get a new thermostat cover gasket as well. Should cost about a buck.