My KK likes to over heat when it idles after being warm for too long. When I drive it's not a problem because the cold air takes the heat away, but as the weather gets warmer I may be in trouble. I definitely do not want to reach that point. I want to troubleshoot as much as I can before taking it into the shop (if necessary). I do know that the problem is that once the engine gets too hot, the aux fan does not kick in to pull the heat off the radiator. I have narrowed it down to a few possibilities.
1. Bad thermometer. How would I check if the current one is bad? And how would I take it out to check it?
2. Bad fan motor.
3. I just thought of this today, but what about a blown fuse or something? and how would I check that also?

I'm hoping it is either the thermometer or fuse because the fan motor is about a hundred bucks.
Any and all help would be greatly appreciated.

To check the fuses would be easy..

Pop your hood and inspect the fuse box on top...
You can manaul pull each one and took
or
Get a test light
or
get a fuse checker

Other will talk about your other request.
You search for the service manaul and read how to run these test as well...

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2008 Liberty Limited 4X4 Command Trac 2
All stock Auto with 235/60/18

Check your fuses first.

J19 (Yellow 60 Amp)

And your relays. It wasn't the fan relay, but I have burn one in the KK before.

There is one relay in the fuse box and then there is a second relay that is mounted on the right side of the radiator by the headlight.

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2008 KK Liberty Sport NIGHT OPS EDITION + GILLS
OEM & Custom Skids - Factory Tow Package - Rock Lizard Skink Super Sliders
Prototype JBA 4 Inch Lift - JBA UCA's - Flowmaster Super 44 OR - Whacked Resonator
Jet Stage 2 - RL Gecko Basket Rack - Custom Winch Bumper - Recon 10.5K Winch

Ditto, it's pretty hard to burn out the fan motor. They'll actually tear up their blades during a water crossing before they burn out.

As for the thermostat, the easiest way to check that it's good is to remove it and put it in hot water on the stove. Use a thermometer (My dad used a candy thermometer on his Ford) and if it opens at the correct temperature, you're good to go.

Now, if all those things are good, then you might have more expensive/annoying problems...like a clogged radiator or something...

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2008 Jeep Liberty, ABS Cut-off Switch, 235/70R16, Trans Temp Gauge, Oil Pressure Gauge
Hanging in Vancouver, WA

Don`t forget to always start with the basics, make sure your rad is clean of debris in front, in between the rad and ac condensor and even pass the garden hose with max pressure in the rad fins from under hood towards the front of the truck.I have seen quite a few cars and trucks overheating from simply a dirty or obstructed rad.

I know for a fact that everything is clear of debris. I just checked that I received my new thermostat in the mail today and I really want to put it in to see if that fixes it. Can you guys tell give/show me a how to for that?
Also, I am pretty automotivly challenged. I have no earthly idea what the relays look like. And what is the differences between bad relays vs. good relays. Pics would be great. Thanks everyone for the help.

I really don't think it's your T-Stat.

As far as what the relay looks like:

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2008 KK Liberty Sport NIGHT OPS EDITION + GILLS
OEM & Custom Skids - Factory Tow Package - Rock Lizard Skink Super Sliders
Prototype JBA 4 Inch Lift - JBA UCA's - Flowmaster Super 44 OR - Whacked Resonator
Jet Stage 2 - RL Gecko Basket Rack - Custom Winch Bumper - Recon 10.5K Winch