So riding to work this morning the temp gauge would move quickly from warm to hot to cold and back.

Do you guys think this is the sending unit or thermostat or something else?

The coolant level was good.

It was cold this morning. 10 degrees or so. But the jeep warmed up nicely before I started driving.

It started this after 10 miles or so and kept doing it the rest of the trip.

Randy

Sounds like a bad sending unit? Temperature cannot change that quickly back and forth driving down the road.
Change the sending unit and if it still does it, I would start looking closely at the wiring harness...

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I have seen thermostats do this when it very cold out. It stick closed, the radiator gets super cold, the engine hot and then the stat opens and cold coolant rushes in and hits the sensor driving the gauge down.

My thoughts exactly.

Where is that thing located by the way?

So is the thermostat difficult to replace?

I recall reading something about it being different than normal?

The thermostat is on the right side of the engine, near the viscous heater and in front of the turbo. It's sealed inside a housing that looks sorta like a carburetor off a small engine. The coolant temperature sending unit threads into the thermostat housing.

It's held to the head with 3 bolts, plus another one that attaches it to the viscous heater mounting point by a small steel bracket. You may need to remove the viscous heater to get to the front thermostat-to-head bolt; can't remember. The biggest pain in the butt is scraping the old thermostat gasket off the head (which is aluminum so be careful not to damage the mounting surface).

So I see the Thermostat with housing on IDparts as a unit. Is just the thermostat available anywhere?

THey are out of stock on Rockauto.

Unfortunately, the stock oem thermostats are not serviceable and you have to purchase it as one unit with the housing.

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Other options are available, there is a serviceable housing that you can manufacture yourself using an old thermostat core, or there is a different serviceable housing manufactured by a member here who I'm sure will eventually show up and push you toward his product.

If you are looking to use the OEM, it will be a complete unit inside a non-serviceable housing. No matter who you buy it from it will probably only last about 40,000 miles, but above all else, do not purchase one manufactured by crown. They are complete crap and have a habit of failing closed which can damage the engine.

The serviceable housing options are expensive the first time, but when the universally cheap thermostat itself inside them fails, replacement is about $12. What makes the factory thermostat expensive is simply the housing. The actual thermostat inside it is the same $12 parts, you just cannot change it your self in the factory design.


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Thanks for the info.

I am convinced now what I am seeing is the sending unit. I got in and the engine was cool and it still fluctuated to hot and back to cold.

New sending unit is on its way.

And if that doesn't fix it, like WWDiesel said, check the wiring. Could be a broken wire making intermittent connection, or a wire that's rubbed through its insulation and is shorting against something else.