Fst96se

Hey guys, I recently picked up a new to me 2015 Rubicon. I really don’t know any history on it, 130k miles. And it is overheating on me.

I have done the block test a couple times to see if there is exhaust in the coolant, and it’s come back negative each time. There is NO oil in the coolant. NO coolant on the oil. No white smoke.

Swapped thermostat (MOPAR AUTHENTIC), used a funnel to fill the block from the thermostat hole before replacing the thermostat. Had front wheels on blocks with front of engine elevated used burping funnel to burp it for quite a while. Got some bubbles out, but then no more bubbles until the fluid and the burping funnel started to boil. Turn the car off, let it cool down, burped a couple more times just like that.

Ran the car for about an hour, drove around for about an hour, great heat, no issues with temperature at all. Pressure in upper radiator hose felt fine. No over pressure.

Turned the car off with the reservoir level at just about the max fill line. Left radiator cap on went to bed to let it cool.

Came back to the jeep in the morning, and the level in the reservoir had not dropped. Started at the Jeep, went for a drive immediately. Had warm air coming out of the vents very quickly, temperature climbed pretty quick. Shortly before 203°, I lost heat. ****I wonder if that was when the thermostat opened and maybe pushed an air pocket to the heater core and then water quit flowing?****

Temperature continued to climb past 226, fan turned on, temperature claimed to 238, fan ran on high. Very, very high pressure in upper radiator hose, upper radiator hose is cold. Coolant reservoir begins to overflow and spit coolant out. Coolant in the reservoir is barely lukewarm.

Thinking I had air bubbles that I could not get out, I took it to a repair place that did a machine flush and vacuum fill. Drove it for a couple hours, temp was great Parked it and let cool completely, and then had the EXACT same issue as listed above

Did my own burping again, and repeated the exact same scenario listed above.

anybody have any thoughts? Think it’s pulling in air from somewhere when it cools, rather than pulling coolant from overflow?

I REALLY don’t want to be a head gasket issue Really.

My next step is to take it the local Jeep whisperer and have do a pressure check on the cooling system to look for leaks

fowlken8

This sounds exactly like my issue. The perfect temps followed by awful heat. Loss of heat at random times. I burped it like crazy. No air. Then there would be air. Passed combustion test. Pressure test was good too.

I replaced my thermostat. The oil cooler housing as well. Then suddenly had insane amounts of pressure in the radiator hose and overheating.

The shop verified it was my head gaskets. So now I'm getting a low mileage engine installed. Thousands of dollars and months of headaches chasing down the issue.

MountainTrails88

I'd replace the radiator cap. Those things are engine destroyers. Now that I think of it, I had the same problem last year. Overflow level stopped stopped responding. Replaced the cap and it works again.