Hi! I am the original owner of an 2003 TJ. I have no auto repair skills but have taken it upon myself to learn how to do some basic repairs. Last week I replaced the windshield frame and glass. This weekend I think the thermostat? When I drive the car for the first time in the morning after 10 minutes the gauge goes right into the red. I pull over, shut if off and turn it back on and it drops right back down to normal levels. The rest of the day while I drive it moves a little to the left and right of the middle on the gauge but I don’t have any other issues. I check my coolant levels every weekend as I have a heater core block/ leak. I replaced my radiator in 2016 and my water pump was professionally replaced last winter (2018). I’m thinking hermostat so I ordered a Stant from Amazon. This is my first post if anyone can offer an opinion I would appreciate it. Thanks!
Thermostat issue?
- Thread starter SGTJ
- Start date
The question is, is it actually overheating, or is it possible the temp sending unit is just bad, and therefore making the gauge act wonky.
Have you checked the radiator itself when it's cooled down to make sure the radiator is 100% full, not just the coolant overflow bottle?
Have you checked the radiator itself when it's cooled down to make sure the radiator is 100% full, not just the coolant overflow bottle?
It sounds like the thermostat is defective, Stant was a good brand choice for the replacement. Make sure you have a new gasket, don't use RTV. Also spend enough time to get the thermostat's gasket seating surfaces absolutely pristine. Scrape all the old gasket material off and use a small wire brush to finish the cleaning. Don't overtighten the two housing bolts either. A 3/8" drive ratchet wrench is the biggest size to use, don't use a 1/2" drive which makes it too easy to overtighten the bolts. 
Okay, in that case it likely is your thermostat like Jerry said. And yes, Stant is the best choice!
It sounds like the thermostat is defective, Stant was a good brand choice for the replacement. Make sure you have a new gasket, don't use RTV. Also spend enough time to get the thermostat's gasket seating surfaces absolutely pristine. Scrape all the old gasket material off and use a small wire brush to finish the cleaning. Don't overtighten the two housing bolts either. A 3/8" drive ratchet wrench is the biggest size to use, don't use a 1/2" drive which makes it too easy to overtighten the bolts.
Good advise here. one thing I will add from my experience when your cleaning the gasket surface also take a small flat screw driver or something like it and make sure there is no crud built up where the thermostat seats in the head. This shouldn’t be an issue but when I installed a reman head the other day the reman had some crud there and it kept the thermostat from seating properly resulting in a leak and ruined my new gasket.
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Be very careful using anything pointy like a screw driver. You don't want to gouge the mating surface.
Yes. I wasn’t suggesting using a screwdriver on the gasket surface what I’m taking about it where the actual thermostat seats inside the head, the thermostat seats in a little notch machined in the head and if that notch has any foreign material in it the thermostat will not seat and your thermostat housing will not mate with the block evenly and it will leak/ruin your new thermostat gasket.
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It sounds like the thermostat is defective, Stant was a good brand choice for the replacement. Make sure you have a new gasket, don't use RTV. Also spend enough time to get the thermostat's gasket seating surfaces absolutely pristine. Scrape all the old gasket material off and use a small wire brush to finish the cleaning. Don't overtighten the two housing bolts either. A 3/8" drive ratchet wrench is the biggest size to use, don't use a 1/2" drive which makes it too easy to overtighten the bolts.
Thank you Jerry! I will pick up a new gasket this weekend and appreciate the cleaning advice and the recommendation on the drive. I would not have known that.
SG
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