Does Thermostat Brand Matter?
 

I was driving my wife’s 1999 Cherokee SE around today in the sunny climate of Atlanta Georgia and the temp gauge redlined at a red light. I shut off the AC and continued on my merry way. About a minute later the gauge was back to the the normal 110 degrees it likes to run at. I turned the AC back on and all was well. A few errands later it did it again. So I think it is new thermostat time. I researched several overheating threads and think this is the way to go as the fan clutch is good and I flushed the radiator a few months ago.
The Mopar thermostat part number I came up with is 52028186AC. But there are a butt load of other thermostats out there. If there’s an upgrade model that would be better I would like to use it. Am I looking for one that opens at 195 degrees or lower? Any brand or is OEM preferential?
Also there was mentioned in a thread of taking a reading with a infrared thermometer. Where on the motor would you put the laser dot on for the best accurate results?
Thanks,
Kevin

First question. Do you have a fan shroud on it? It's an absolute necessity on a Cherokee! I've always used Stant Superstats in every car or truck I've ever owned and only had a problem once because it stuck open. A 195* is OE for proper fuel management purposes. Is the electric fan coming on, especially with the A/C?

The Mopar stat has an air bleed hole in it, but if you properly fill the system you don't need that. The way I've had the best luck filling it is to remove the temp sensor and fill it until coolant runs out of the hole, screw it back in, and continue filling it. That gets all of the air out of the head to start with. After it warms, you might need just a bit more.

Another option is to install a fan over-ride switch to keep the fan on constantly when you need it. You still need a shroud!

Mopar is definitely recommended for the thermostat. It's not quite as critical as a CPS (meaning, you MUST use the Mopar or are asking for trouble), but if Cruiser54 recommends it (which he does), you aught to do it.

I've run a Stant t-stat for the last year or so (I hadn't known that Mopar was recommended) and so far so good - but I have a Mopar t-stat that will be going in the next time I'm doing anything cooling system related.

For infrared temp gun use - the best place would be to hit the t-stat housing (especially on a 99) and compare the reading to the gauge. After 96 the gauge uses the engine sensor (aka CTS - the one plugged into the t-stat housing) for both engine management and running the gauge. This is opposed to the earlier design that had the engine management sensor in the t-stat housing and the gauge sensor plugged into the rear of the head.
Of course, you can check the temp at multiple locations on the head and block just to see if there's any gross inconsistencies at different points. The spec engine operating temp is 210, so you should see temps that reasonably reflect that for the block and head - the exhaust manifold gets quite a bit hotter than that, so be careful not to get a bad reading and freak yourself out.

Edit -- Also, Dave's advice regarding having a complete fan shroud is spot on and I fully agree with him.

The fan shroud is there and complete. I took it out for a spin this evening and the electric fan came on when the AC was turned on. I did not listen for it when it was overheating. The Mopar 195* thermostat will be ordered. I am sure this will solve the problem.
I wil use my laser to check the gauge. That will be an interesting test.
Thanks for the reply’s
Kevin