94formulabird

So first off this is my wife car so I have no idea how long this has been going on. She is at the point in her pregnancy where she can no longer reach the pedals in the Jeep due to moving the seat back to accommodate her growing belly. So she is driving my truck and I'm Jeeping it for the rest of the summer.

First thing I noticed while driving is that the fans are SCREAMING. I assumed with the summer temps that it was running a little warmer and keeping the fans on. I then noticed that the temp gauge is moving between the 1/2 point (where it normally lives with zero fluctuation) to the 3/4 mark and I'm seeing temp readings up to 250F. Then they fall back to 210-220 just as fast as they rose. This only happens while driving. Idle temps are 210-220. When driving within 1-1.5 minutes the temps creep from 210 to 245-250 then within 1 minute they fall back to 210-220. No coolant leak (puddles) but I can smell it.

I just replaced the tstat and housing and it didnt fix it.

I guess next easiest replacemnt is temp sensor?
Then radiator or waterpump?
Then heater core?

Jeep has 80k miles and has been "offroad" for camping 3 times (i know...i know....)

resharp001

Especially since you just replaced the thermostat, I'd question if you got it burped good enough. Even a small bit of air in the system can cause issues. Since the radiator cap is on the passenger side, sometimes it helps to jack that side up a little so air bubbles travel up to it easier. There is also a bleed valve on the thermostat housing. I'd just verify you don't have any air in there for starters. Neither a bad radiator or a bad heater core would exhibit those swings in coolant temps. I'd think if the WP wasn't working, you have major issues that would not allow the temp to drop back down to normal. the coolant just wouldn't be circulating like it needed to.

rob_engineer

There is a wire connected directly to the battery that goes to one of the fans. I think it is called a fuse link. My 2012 slightly overheated. I discovered that the battery terminal had gotten loose and the fuse link getting intermittent voltage prevented one of the fans from going on.

94formulabird

drove up on a set of ramps in my already angled driveway...burped it good...all issues gone

even drove around in lower gears to keep above 3k rpms to generate heat and it never got above 228

WaterRat72

HOLY SHIZNIT!!!!! This is EXACTLY what's happening to mine. I also have 80k miles. Exact same damn thing. I recently had the radiator replaced and this has been driving me bonkers.
Burping mine first thing tomorrow morning!

To be clear, to "burp" it, you simply jack the car up on the passenger side and unscrew the radiator cap (not fully remove) correct?

karls10jk

I removed my cap when doing it so I could add fluid at the same time, but yeah, same general concept. I put the front corner about 18" off the ground. I don't recall the 3.6 having an upper hose that you can get a good squeeze on to force air out but the 3.8 did and that's where you'd find air hiding.

resharp001

Anytime you mess with the cooling system (replace water pump, heater core, thermostat, coolant temp sensor, replace radiator), you are highly likely to get a little air trapped in the system. Unless you are using one of those fancy gizmos that help bleed the system, it usually takes a couple attempts to get it all out IMO. IDK about the 3.8L, but the 3.6" has a bleed valve on the thermostat housing. I usually open that up and start the jeep....leaving it open till it stops bubbling and coolant is streaming out. Then I move to the radiator, remove cap completely, and do the hose squeeze trick. You have a little time after starting the jeep to get air out and add coolant or water before the level starts rising up on you. Again, you're gently pouring in a little water/coolant as you're getting the air bubbles out. As soon as that level is really rising up and about to pour over the top of the radiator, get that cap back on...at which point put the cap on and let it cool down again. repeat. Even a little air in the system causes weird things to happen.

WaterRat72

Holy crap, any idea of how to get the radiator cap OFF?? I unscrewed it and a slight release of air but it's not coming off. What gives? Once unscrewed it should just pop straight up and off right?

resharp001

Obvious statement here, but you're surely doing this with a cold engine. Once you twist it, you should have to press down and twist it a bit more before it lifts off.....kinda like a Rx medicine cap.

WaterRat72

Yes of course cold... I'll go out and give it a shot and report back feeling like a complete moron.. stand by...