1991 jeep cherokee larado * over heating *

My Jeep only overheats when going up steep grades.

Could it be a sensor or fan problem?

Coolant not leaking & no signs of spay inside of engine.

Are you loosing any coolant? Does the radiator fan come on? Are you using A/C? Does a fan on the radiator come on when you turn on the A/C? What would happen if you turned on the A/C when going up the hills?

If this vehicle has an engine-driven cooling fan (as opposed to electric), make sure the fan clutch is working correctly. On a vehicle this old the clutch could be bad and the fan might not be drawing air through the radiator the way it should.

When was the last time the thermostat was replaced?

Thanks for the reply!
No I am not losing coolant. When I noticed it over heating I turned on the heater on to pull the heat from the engine (trying to avoid cracking the head) & it seemed to lower the temp with in a safe zone.

I didn’t risk turning on the A/C at this point however the first time I noticed it over heating it was when I was climbing a steep grade with the A/C on, however overheats with out A/C on.

not sure when thermostate was replaced, just bought this jeep & thought I did a very careful inspection however didn’t drive up steep hills…