Does it run hot in traffic but cools well on the freeway or runs hot under both conditions? Both Wrangler engines use a viscous coupling fan hub. As the engine gets hot in normal traffic the "gel" in the fan hub expands and locks up the fan allowing it to draw air through the radiator cooling the coolant in the engine where it circulates through the engine when the thermostat reaches a sufficient temperature at which it opens. In normal traffic the viscous coupling fan is responsible for keeping the engine cool. If the engine over heats in traffic, and the thermostat is working correctly (it opens at about 190 degrees Fahrenheit) and the water pump is capable of circulating coolant around the engine and radiator then perhaps the the mechanical fan hub is not working correctly. At freeway speeds rush air flowing through the radiator is sufficient to cool the engine if the radiator is not restricted internally or the core of the radiator on the outside is not blocked with debris. Does the engine loose coolant if so look for a leak. The way an automotive shop would locate the leak is by removing the radiator cap and attaching an adapter that screws on in place of the radiator cap. Something that looks like a bicycle pump with a pressure gauge attached to it is used to "pump up" pressure to simulate pressure generated when the cooling system is at operating temperature, the leak is then found sometimes it is obviously leaking from a coolant hose or cracked housing, failed gasket or water pump, sometimes the engines cooling system needs to be inspected from below or inspected using a mirror and flash light. A blown head gasket is also a possibility, The most accurate way to test for a blown head gasket on a gasoline engine is to test for the presence of carbon monoxide in the cooling system. Snap-On, Matco (part # CO 2000), and Napa sell a tool to check to carry out this test. Another link to a supplier of this tool is http://www.etoolcart.com/combustion-leak-detector-lis75500.aspx. Carbon Monoxide is only present if there is a blown head gasket or cracked cylinder head. http://www.arrowheadradiator.com/head_gasket_or_combustion_leak_test.htm I think the napa part number 700-1006. http://www.blockchek.com/instructions.htm . Signs of a blown head gasket are coolant loss (frequently have to top up the coolant level of the engine without seeing an obvious leak), experiencing over heating or rough engine running or the presence of white sweet smelling steam from the exhaust. A badly blown head gasket may allow engine coolant and oil to mix.
In the case of a blown head gasket, how often would the overheating occur? would it be extremely frequent on every operation of the vehicle? Would there be visable signs on the block somewhere? The reason I ask is that I have been having an overheating problem that has me stumped. It started to show up only at slow speed while trail riding, The water pump was repleced, the system was flushed, the clutch fan is ok. I cleaned out the rad and it seemed to go away but; last week the overheat occurred at highway speed while under no stresses. Now I am suspecting the thermostat, but I have smelled the sweet odour at times. No visable signs of a coolant leak are present nor is the white mist from tail pipe. Ideas?