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Thermostat Advice

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I have a 1990 Jeep Comanche 4.0 Automatic Long Bed. The temperature keeps climbing into the red zone. Normal operating temp seems to be 210. I've also notice that the back of the engine block (which matches the gauge I can read in the truck) is hotter than the front of the engine block by about 40 degrees which is hotter than the sensor that plugs into the thermostat by about another 30 degrees. I had a buddy with one of those lazer temp sensors check it out.

I had a 190 thermostat, it was relatively new. At this point I've put it back together without a thermostat and it seems to run cooler. It just seemed like the thermostat wasn't opening up correctly.


Suggestions on the best thermostat and the temp it should open??? Any other ideas?


It's an open system with a radiator that is less than 1 year old. This is one of those problems that just won't seem to go away.

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A 195 degree OEM T-stat from the stealership is what I run (and I work at oreillys). I would NEVER EVER run any T stat cooler than the OEM, not on an EFI engine anyhow. Your Tstat opens up at 195 so if the engine is getting hotter than that then the thermostat has nothing to do with that (assuming it is functioning properly). If you run a cooler tstat than it will stay in open loop mode permanently and your gas mileage will suck.

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:agree: OEM 195*



Make sure you fully bleed the air pocket that tends to form at the rear of the engine. :thumbsup:



That is why the back of his block is hotter. I would convert to "Open Cooling" and never look back.

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Park it facing down hill, let it cool, and pull off the temp sensor at the back of the head. From there, start it up, and let it run until coolant starts coming out that hole. Once it starts coming out, and no air is burping from the system, put the sensor back in, and top off the rez bottle.


Rob L. :thumbsup:

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