I have a 1995 jeep cherokee straight six or 4.0 liter where is the radiator thermosta soo i can replace it

Hi, It is actually called an engine thermostat, as it regulates coolant flow through the engine. If you follow the top large hose coming off the radiator to where it connects onto the engine, you will find a housing there connected to the engine with 2 bolts. There may be another hose connected to this housing also. You will lose a bit of coolant when doing this, so use a bunch of rags under the work area and a catch pan beneath the vehicle.
Parts needed: Thermostat, gasket, tube of black RTV sealant, new clamps for hoses if they look rusty or do not have good resistance on removal. (for factory spring type clamps)

Procedure:
Remove hoses from housing and bend back and tape back out of the way (use some cable ties if you wish) to keep coolant from running everywhere and so they are out of your work area. Remove 2 bolts holding the thermostat housing to engine. Gently tap housing with rubber hammer to break the gasket seal on housing. Once housing is off, you will find the thermostat underneath. Remove thermostat from engine. Clean the housing and engine mating sufaces of all traces of gasket material. Surfaces must be clean and dry before re-assembly. Use a rag to soak some coolant out of engine side hole to facilitate cleanup. Scrape off gasket material and use brake cleaner to wipe off residue and dry with clean shop rag. There are 2 types of thermostats for the jeeps, one has a rubber seal around the thermostat, and requires no other gasket, the other has no seal and requires a separate paper type gasket to be sealed to the mating surfaces. I believe the straight 6 has the paper type. Install thermostat with spring end into engine cavity. Put a thin even coating of black RTV sealant on the engine mating surface. Place gasket on RTV coated surface, aligning the bolts holes to holes in gasket. Apply thin even coat of black RTV sealant to thermostat housing mating surface. Put a small amount of RTV sealant on threads of bolts (clean them first) coating the entire thread. Put housing onto engine and install bolts finger tight - firmly seated. Allow RTV to cure for 5 minutes. Some RTV will squish out, thats OK, but use the RTV as a THIN EVEN coat, as you dont want a bunch of excess sealant in the thermostat cavity. Torque bolts to 16-20 ft. lbs. or a good wrist tightening. DO NOT overtorque, as you will either crack the housing, or cause warpage making your gasket leak. Re-install hoses and tighten clamps. If spring type clamps were on the hoses, replace the small clamp with a band type clamp. If large clamp installs tightly, it can be reused. If it was rusty and goes on rather easily/weakly - replace with a band type clamp. Refill - check coolant level, add as needed. Start engine, allow to reach operating temperature and check for leaks. Done!
Please rate this answer! Thanks, Mike

Your thermostat is inside the housing at the engine end of the top radiator hose. Make sure you put the spring end into the engine when you replace it. Engine running temp should be around 210 degrees (f) and most times it's best to use a 195 thermostat. After you get it installed, make sure that you run the engine with the heat on full high and that you top it off after the stat opens. You don't need to drain the system to change thermostats. You won't loose very much since it's high up on the block. Don't open the system 'till the engine has cooled down and isn't under pressure.