When I bought my 93 XJ, I replaced the radiator, thermostat, thermostat housing, water pump, radiator cap, and radiator hoses. Everything was going fine till about 2 days ago when I noticed the auxiliary fan was always running. I just checked the entire engine bay with an infrared thermometer and found everything was as it should be. However the radiator hoses were around 170*, and the thermostat housing, especially around the coolant temp sensor, was around 240*. What do you guys think? Faulty thermostat? Faulty water pump?

 

air in the system? bad head gasket?

 

Don't know how air could get in the system.. I haven't opened the radiator cap since I installed it almost a year ago. Not sure about the head gasket.. everything runs smooth and sounds the same

 

temps here have dropped 15* to 20* as well, if that effects anything.

 

My guess would be a sticky thermostat water pump would have different symptoms how long has it been since u did the work to the cooling system? An air pocket will also cause this to happen if the work was done recently i would lean toward air pocket being the problem.

 

Also a head gasket that is allowing exhaust heat and pressure into the coolant passages will create super heated air pockets in the cooling system. This is easy and/or cheap to have tested.

 

I did the cooling system overhaul almost a year ago. I had the ac system done at a shop a few months ago, but everything was fine till I started driving it daily these past few days.

 

how can I test this myself?

 

Might want to remove it (motor COLD) just to check coolant level is at the top.

 

Theres is a kit you can buy that detects a blown head gasket at most auto part stores it looks like a beaker with a rubber boot on the end and holds a blue solution that will turn yellow if it detects exhaust gasses in your cooling system. Dont try this unless you are postive that the entire system is in proper working order and that u have run the engine with the cooling system open and allowed it to burb free of air. To do this run the engine from cold start till the engine temp stabilizes near thermostat temp rating while the engine is warming up observe coolant behavior (get a funnel that mounts to the radiator fill opening at a parts store) the coolant should burb any air on its own and after full warm up the coolant level in the funnel should be stable and you can see the coolant pumping no bubbles. If you have bubbles that wont go away use the kit to check for a blown head gasket.

 

wouldn't i notice a loss in power and actually be able to hear it if the head gasket is blown? everything runs and sounds like normal, no overheating/white smoke anywhere. the secondary fan stays on when it warms up because the area around the sending unit (thermostat housing) reads at 240*

 

the exhaust gases leaking from the head gasket makes sense considering the exhaust manifold is right next to the thermostat housing/sensor.. i think i'm going to try adding some bars head gasket sealer to see if that helps. not sure which one though.. any recommendations?

http://barsproducts.com/catalog/view...stop-leak-1109

or

http://barsproducts.com/catalog/view...g-sealant-hg-1

 

I wouldnt use bar leak personally its a band aid for something that needs stitches and could plug heater core or radiator.