What does the temperature gauge say?

 

It ranges. between half and 3/4.

 

Look fir a leaking water pump or thermostat housing. It’s not holding pressure. Check your coolant level as well.

 

My coolant resevoir was empty yesterday. It has been in storage since October. I drove it some today and coolant level is the same. (Full)

 

It also would not hurt to change the thermostat.

 

Normally when the fan comes on after a few seconds/minutes of starting. There is either air in the coolant lines, or a stuck thermostat. There is a bleeder valve on the top of the thermostat. You may have to remove the air intake to get at it, then use a screw driver to turn the bleeder valve to release the air until the cooler starts spitting out. The front end of your jeep show be at an incline while doing this. If it did not fix the problem, It's a 20$ part on amazon, and 2 bolts to remove and replace and you may need a 15$ jug of coolant after reinstallation.

Mechanics/Dealers will charge 150/200$. Hope that helps!

 

2012 2-dr JK - I actually just had my thermostat changed and that's when I started having trouble with the fan always running on High. On Start, it is fine. But driving it up my road at 35mph, in no time it's kicking on High. Once it gets on high speed, the temp fluctuates between half to 3/4 hot. No exertion on the engine=doesn't matter if AC is on or not. Doesn't matter if its 79 degrees out or 95. Same problem. The fan kicks on High and won't settle down. And there is no reason for this. Only started after resolving the P0128 code- thermostat swap out. Fixed that but now this! RIDICULOUS issue. It is Not popping an error code- and that's probably more frustrating. LOL.
I found these articles that gave a lot of information to check for Grounding and some other things. I appreciate the above info about the air in the lines.
1. Jeep JK radiator fan high speed issues.... fixed and explained. - Quadratec Jeep Forum
2. Diagnosing a 3.6L "Pentastar" Jeep JK Radiator Fan Issue (Code: P0480)

I don't have to tools to diagnose so I'm running it up to the dealer to trace it this week. I printed the articles so I can have a convy if they tell me "Normal".

 

2012 2-dr JK - I actually just had my thermostat changed and that's when I started having trouble with the fan always running on High. On Start, it is fine. But driving it up my road at 35mph, in no time it's kicking on High. Once it gets on high speed, the temp fluctuates between half to 3/4 hot. No exertion on the engine=doesn't matter if AC is on or not. Doesn't matter if its 79 degrees out or 95. Same problem. The fan kicks on High and won't settle down. And there is no reason for this. Only started after resolving the P0128 code- thermostat swap out. Fixed that but now this! RIDICULOUS issue. It is Not popping an error code- and that's probably more frustrating. LOL. I found these articles that gave a lot of information to check for Grounding and some other things. I appreciate the above info about the air in the lines. 1. Jeep JK radiator fan high speed issues.... fixed and explained. - Quadratec Jeep Forum 2. Diagnosing a 3.6L "Pentastar" Jeep JK Radiator Fan Issue (Code: P0480) I don't have to tools to diagnose so I'm running it up to the dealer to trace it this week. I printed the articles so I can have a convy if they tell me "Normal".

What did you find out? I have the exact same issue as you do and I haven't been able to figure out the issue yet.

 

What did you learn I also have the SAME issue.

 

Hello, my issue ended up being, believe it or not, a small leak in the radiator in each corner. Dealership wanted $800 for the radiator alone and then several hours labor to install it. I got our local mechanic to do it instead. Radiator from O'Reilly's was around $160. We also got the thermostat and housing changed as well. Jeep is running perfectly again. Fyi, you pretty much have to remove all the front plastics to get the radiator out. It's a major pain.

 

The dealership told me that when the vehicle detects a leak in the cooling system it changes the fan operation to run on high all the time in an attempt to keep the engine from overheating. I questioned them on why in the world a code wouldn't be thrown for a leaking system and they told me it couldn't be done. I responded by saying if the system detects a change and then changes the way it operates to compensate, a code could absolutely be added to database table to inform the driver of a problem. Poor engineering in my opinion.

 

Jeremy, thank you for the Update to share results, and help inform those other jeeper's with similar problems.
There must be a cooling system pressure sensor that switches on the high speed fan circuit.
All very simple for a systems-designer to plan for.

My son had taken his '08 Tundra with 5.7L V-8 to his mechanic for replacement of a leaking water pump.
Lo and behold, the radiator core had cracks on opposite corners due to vibration.
He had a new radiator and pump installed, and no issues since in two years time.

 

There is no cooling system pressure sensor.

It is as simple as if pressure is not adequate then temperature increases and this the fan switched to high speed to compensate.

 

The fan kicks to high because your PCM either detected high enough coolant temps or high enough AC condenser pressures. . It has nothing to do with pressure on the cooling system side. There is no pressure sensor on the cooling side. It can have everything to do with AC condenser pressures though.

Is your AC on when you detect this?