Welcome to the group;

... If the thermostat is sticking the system would run hot with or without the A/C on. The radiator drops the temperature and this causes the lower hose to be cooler. My ‘99 3.3 has an electric fan as well as a belt driven fan. The electric comes on when the A/C is running. because the refrigerant puts a lot of extra heat into the radiator.

...My ‘99 Grand Cherokee was set up just the same. Check that the fan is operating correctly. It may be time for a radiator flush and new coolant .

Air trapped in the system?

Pressure or coolant leak?

Factory recommended coolant mix?
Overflow bottle filled?

Is the shroud installed?

Is the fan in proper position in shroud?

A big spring in the lower intake hose? To prevent it from colapsing

Thermostat stuck closed?

Thermostat right side up?

By-pass coolant flow blocked?

Heater core flow blocked?

Fan clutch not engaging completely?

Is the fan clutch HD?

Is a replacement electric fan under powered?

 Fan belts properly tightened?

Idler pulley bearing frozen up?

Got small under-drive pulleys?

Coolant temperature Sensor having issues?

Is the temperature gauge having issues?

Is the water pump impeller, bearings or seal having issues?

Is the pressure cap tight and working?

Air dam installed?

Is there strong airflow over the exhaust manifolds?

Have scoops or louvers changed airflow under the hood?

Has the carburetor cool air intake been removed?

Bugs, dirt or wrong type of paint in cooling cores?

Is the core large enough for engine mods?

Rust or scale in the coolant?

Are rust or scale deposits lodged in the passageways of the heads or block?

Are tubes in the core blocked from old repairs?

Air baffles properly installed near the core?

Is timing (vacuum advance and centrifugal advance) and tuning properly set?

Is the catalytic converter and exhaust free flowing?

Is the exhaust heat riser working correctly?

Is an automatic transmission problem putting extra heat in the radiator?

Are A/C and oil coolers adding more than normal heat?

Is the gear-ratio proper for highway driving?

Are the brakes dragging?

Attention Greenies: The government is allowing importation of merchandise from countries that are polluting the atmosphere worse than our country is. This importation costs the U.S. jobs and make our borders less secure. Just one of the millions of un inspected container loads could disrupt our economy and life as we know it! Go hug a tree in China!

Yup! The proper thermostat is extremely important to help keep the engine oil in good condition.

... However they might have removed it because of overheating from some other problem. The thermostats job is to keep the coolant warm enough but can’t prevent over heating and, if working correctly, can not cause overheating. Lack of a thermostat can cause water pump impeller cavitation and over heating.

Corn Ethanol: Our government is hoodwinking Americans and making a few people rich. We have a 50 cent per gallon tariff against importing ethanol and subsidize our ethanol refiners 54 cents per gallon with our tax dollars. And using Corn Ethanol will drive food prices up! Another case where lobbyists make the laws!