Jeep Wrangler Overheating Solved – How we did it

Why is my Jeep Wrangler Overheating? 

There are many reasons you may find your Jeep Wrangler overheating. In our case, several of them combined to make things pretty interesting. Many of us are guilty of transforming our Jeeps into heavy, aerodynamically challenged wind-bricks - our Jeep (3.6 JK) included. While these modifications may be the culprit, the first thing to do is check all the common problems. If they are all OK, there are a few mods that can offer a solution. We'll go over the things to look for first, then get into the modifications we've done to keep ours cool.

Things to look for

Coolant level

The first thing to check is coolant level in both the radiator and the reservoir. If the reservoir has coolant and the radiator is low, you may have bigger problems. This could be as simple as a bad radiator cap or a damaged reservoir hose. In our case, low radiator level was due to a failed head gasket that pushed exhaust gas into the coolant overflowing the reservoir. If you suspect a head gasket, you can perform an exhaust gas test to confirm.

Radiator Cap

Next we'd check the radiator cap. If it isn't maintaining appropriate pressure, the coolant can boil at a low temperature preventing it from absorbing heat properly and often pushing it out of the radiator. 

Properly bled system

Another thing to check is that the cooling system is properly bled. It is not uncommon for people to perform cooling system work and then fail to properly bleed all the air out of the cooling system. This can cause the thermostat to remain closed well after it should open, resulting in overheating. On the 3.6 JK there is a bleed screw on the thermostat housing that needs to be opened to release air. This is best done while you have a special bleed funnel installed in the radiator to allow more coolant into the system.

Thermostat & water pump

If those check out, verify the thermostat and water pump are working. With the engine coming up to temp, check the radiator hose leaving the thermostat. If that hose doesn't get hot when the engine reaches full temp, one of those is likely the culprit, and I'd bet on the thermostat first. If you've got a 3.6, I'd highly recommend only running a genuine Mopar unit as poor performance with aftermarket thermostats is very common.

Coolant condition/contamination

One more thing to look into is the condition of the coolant. It is fairly common to find vehicles with incorrect coolant or plain water added. These can both lead to poor performance or even damage. You can check Coolant condition by checking the boiling point using a Hydrometer or a Refractometer, and checking the PH (typically between 7 and 8 is good). Also, if you find signs of oil in the coolant, you may have a failed oil cooler or head gasket. When in doubt, flush it out and start over with a fresh fill.

Air flow & fan

The final thing to cover is air flow. This could be restricted by something simple like a plastic bag sucked into the grille, mud in the radiator, or you could be faced with a failed radiator fan. Just idling the engine should bring the temperature above fan on temperature and allow you to observe fan function - on the 3.6 JK it should come one at 226° F. With Jeeps, it is very common to see aftermarket modifications (winches, aux coolers, lights) obstructing air flow to the radiator. In our case, there was a PSC power steering cooler installed just like the instructions show. Unfortunately that blocks the air flow path to about 1/3 of the radiator - a problem we found a great solution to. 

Factory design flaws

If you have a 2012-2018 Jeep Wrangler, there are some things you should know about the factory cooling system. The gauge stays dead center until the coolant exceeds 230° F - way too hot in our opinion. If you start one and let it idle, it'll get all the way to 226° F before the cooling fans even come on! Also way too hot in our opinion. An aftermarket gauge or tuner can often display actual temperature so you don't have to trust the Lie-O-Meter in the dash. We run a Banks Data Monster to monitor and log various parameters and make educated decisions about modifications. Through LOTS of miles with various mods we've identified a few mods that actually produce results in the cooling department. 

The Superfecta of mods to stop your Jeep Wrangler Overheating

Now if everything on your rig is determined to be healthy, maybe You're suffering from the other problem we had... Many of the things we do to and with our Jeeps are hard on them. Bigger tires, heavy accessories, heavy loads, and towing are all hard on the cooling system, but there's more. Aftermarket bumpers, fenders, racks, rooftop tents, and those big tires we like, are all contributing to an aerodynamic disaster that makes a stock Jeep look like streamlined land speed racer. While a Jeep isn't an aerodynamic masterpiece, making this worse adds load, and the harder the engine works, the more heat it will produce. While these things may be stacked against you, there are the 4 most effective mods that can increase cooling capacity to compensate. These mods are all done on our 3.6 JK, but a variation of each can be accomplished on any Wrangler.

Which modifications are right for you?

If you are looking for a solution to an overheating problem, just know it is a very attainable goal. Just be sure to check all the basics before diving down the modification rabbity hole. If all those things are healthy, but your Jeep Wrangler overheats at highway speeds, I'd do the following. I'd start with flow baffles first, then hood vents, then a better radiator. Finally, fan control does make a small difference at highway speed, but not much. If you mostly overheat at lower speeds, I'd start with Fan control first, then a better radiator, then hood vents.  Flow baffles likely won't do much for overheating at super low speeds.

Our experience

We fought many issues with our 2012 Jeep Wrangler to make the new engine last after the head gasket failed. This failure almost certainly stemmed from cooling system issues. When we installed the new engine, we started heavily monitoring all operating parameters. We found the factory cooling system was not up to the task of shoveling our heavy Jeep around at 80+ MPH, on the trail in 4-low, or climbing grades on small mountain roads. The coolant temperature would skyrocket to 232°+ forcing us to roll windows down, run the heater on high, and back out of the throttle to keep the poor thing from boiling over.

We did the hood vents first because it was easy to do quickly before a trip we had planned. This helped a little. We then did the flow baffle which in our case also removed a flow obstruction. The upgraded radiator was done at the same time since the front end had to come apart to do both. These mods alone solved our highway speed overheating entirely, but the Jeep would still get a little hot on the trail and slow mountain roads - just not as hot as it had before. Finally, we Changed the fan control set-points solving that entirely.

After ensuring our cooling system is very healthy and performing these 4 modifications, our JK happily cruises along at 212° F most of the time with some longer periods at 216° when pushing it at altitude or towing. Sometimes we see 222° or even 226° during a hard pull like accelerating on an uphill onramp at elevation towing a trailer.