JeepNewbie14

New to the Jeep scene. I bought a used Jeep with 115K back a few years ago. It now has a 124k. Last month it started to overheat. I had the thermostat sensor that attaches to the cylinder head replaced, the radiator cap replaced (from Oreilly's) and now it still runs close to redline. I had checked the upper hose and it still stays hot to warm an hour after having parked. The lower hose is cold. Any suggestions? Some have told me a bad sensor, air bubbles n system?

Thanks

Jay2013jk

Welcome to the forum.. Good group on here, friendly and knowledgeable. It is possible that air could be in the system; check this how to "Burp" for air. And from my own experience get a OEM Mopar Rad cap.

JeepNewbie14

Thanks for the advise. I will get one ordered and try that as soon as it arrives.

Mark Doiron

Hopefully burping takes care of your problem. I've had mine overheat a few times in its 297,000 miles. Once it was a mod I had put in to allow me to turn off the fan for deep water crossings, so not likely you have that problem. But another time it turned out to be a bad intake manifold gasket. That's a common problem on the 3.8L motors, but you have the 3.6L. It (and a cracked head) can allow hot exhaust gases into the coolant, heating it up). A final problem I had was just last year when my radiator fan went bad while exiting Joshua Tree Natl Park via the remote Old Dale Rd. It was an unusual failure of the fan in that the fan motor ran just fine. However, the spline that holds the plastic fan to the motor shaft was no longer properly engaging with the fan blade. We could check the fan spun freely to ensure the motor hadn't frozen (a more common problem), but that proved misleading. Bottom line: Ensure that your cooling fan is actually turning.

resharp001

An important bit of information is what your coolant reservoir level is doing. I that level dropping over time? You likely have air in the system, but the question is how did the air get there. You probably have a leak in the radiator. It's a common issue for us and it's usually a pinhole leak that shows now signs till you have everything off the radiator.

john77

I am having the over heating issue as well, before the new motor and after the new motor. New thermostat, new water pump, new radiator, new coolant tempter sensor and I have burped this thing on jack stands on a slanted drive way. Around town it is great, put a load on it above 3000 RPM ether jump on the freeway or an incline and it jumps from normal to 3/4 mark. When I let off the gas it goes back to normal operating temp. I have been chasing this thing for 3 months, dose anyone have any ideas?

Mr.T

There are some ducting seals around the radiator which force air through the rad rather than let air around it. They are a royal pain to install on the 3.8L, and I think it's the same or similar with the 3.6L. Somewhere there was a caution (either with a new rad on in the service manual) to resist the temptation to chuck them, put them back properly or overheating will happen. The other thing that comes to mind are grille inserts or high mounted winches restricting air flow.

john77

They are the same on the 3.6 I forgot to mention that I chucked them and ended up replacing them.

Mr.T

Is the fan running at high speed when this happens? Jscan and some other obd2 tools can force the fan to high speed as a test.

john77

Yes, when it starts heating up the fan kick into high speed.