2018 JLU 3.6 Overheating

[KABx04]

Hi, all! Long time lurker, first time poster. About six months ago, I had to replace a cracked coolant reservoir. I added coolant to replace what had been lost. For the last few months, everything has been fine until recently. The engine temp has been in the 250s and the fan has been running in overdrive. The last couple days I have been getting a warning and light and it’ll jump to the 290s. The heater is intermittently blowing hot air. I assume from what I’m experiencing that the thermostat needs to be replaced. It was quickly apparent that the procedure won’t be the same as my old JKU. Can anyone point me to a thread or video that will help and show how to do it for a JL 3.6? I appreciate any help!

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[jjmarkus]

1. Intermittent blowing hot air indicates air in the system
2. Air in the system could have been by not purged system when you lost coolant and filled reservoir or it could be a blown head gasket.

Watch for excess steam out the tailpipe, especially first start of the day.
Look for milky oil on dipstick or oil fill cap, or steam out the oil fill cap
Look for bubbling in the coolant reservoir, especially when revving up the engine

Curious if it overheated back when had the cracked coolant reservoir? Even if it didn't, and one head/cylinder could have ran hot because of low coolant level and begun the process that lead to blowing a head gasket even a few months later.

Make sure your coolant system is purged and full of coolant. if overheating continues, yes could be a thermostat, but more common on the 3.6 is a head gasket issue.

 

[KABx04]

Definitely not a blown head gasket at this point. I suppose I should’ve asked how to properly purge the system without a cap on the radiator itself.

The cracked reservoir was replaced the day I first smelled coolant. It was a small drip of a leak and luckily the dealer had one in stock. There were no other leak(s) from that day forward. I did top of the reservoir with MOPAR 150,000 mile OAT.

 

[mwilk012]

I wouldn’t say “definitely” because that’s exactly what it sounds like. 250 is too hot. 290 is absurd.

 

[roaniecowpony]

Definitely not a blown head gasket at this point. I suppose I should’ve asked how to properly purge the system without a cap on the radiator itself.

The cracked reservoir was replaced the day I first smelled coolant. It was a small drip of a leak and luckily the dealer had one in stock. There were no other leak(s) from that day forward. I did top of the reservoir with MOPAR 150,000 mile OAT.

There are a number of tests that will give you clues of whether your head gasket is blown. A cylinder leakdown test, used oil analysis, coolant hydrocarbon test, coolant system pressure test. Probably others. You can't say with any certainty the head gasket isn't blown until you do a couple of these. Pick one or some. Or close your eyes and plug your ears and drive it till it lights the dashboard. But yeah, 290 is in the stratosphere.

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