Jeep JK Radiator Upgrade

Why the Jeep JK needs a radiator upgrade. 

Our 3.6 JK loved to run hot, and it eventually suffered a head gasket failure. While replacing the engine and monitoring things closely, we found numerous things that needed to be fixed in the cooling system including PCM tuning, Air flow mods, and the radiator quality/capacity. Now that you know why, read on to learn what, how, and how good:

What Radiator is best to upgrade our Jeep JK?

After MUCH research we settled on the Mishimoto MMRAD-WRA-07V2 Radiator. We chose to source it from Amazon for convenient next day shipping. While there are many upgraded radiators, this one fit our needs best. Some options have strange shapes at the top that make filling them fully difficult, while others cannot accept all the factory plastic shrouds and trim. There are also numerous units that don't seem well enough made, or high enough capacity to be an upgrade over stock. This unit from Mishimoto appears to be very high quality, fits better than the rest (given the added size), and after a few calls to them for various other things, it seems customer support is quite good. Here's a comparison of the stock radiator to the Mishimoto:

Here is a little peek into how we swapped out the radiator in our Jeep

The JK can be a bit of a pain to work on sometimes, but the radiator isn't a terrible job. The thing comes out the top once you pull the fan and other cooling components off. With the air box, intake hose, and grill removed, the rest of the job is pretty quick despite the fact it looks like a disaster in this state:

The only little complaint I'd hav about the Mishimoto is that the radiator fan ends up a little further back due to the added thickness. This posed a minor threat to rubbing our upgraded alternator, so a small trim job to the mounting bosses on the back of the radiator and the fan shroud made for a nice tidy fit:

BLEED BLEED BLEED BLEED BLEED!

Whatever you do, make sure you bleed all the air out of the system anytime you work on a Pentastar 3.6 engine - well, any engine - but especially this 3.6! The easiest cheap way we've found to do this is using a Funnel designed specifically for bleeding cooling systems. We've used this method now on various vehicles, and numerous times on the JK. Open the bleed port on the thermostat housing to let air out from behind it as needed, then simply idle the engine until it reaches thermostat open while ensuring the funnel is full. I think a large number of 3.6 failures are due to people not bleeding the cooling system. DO NOT let that happen to you! Engine replacements aren't fun!

Final thoughts

With the new upgrade radiator installed in our Jeep JK, along with the other mods, temperatures have remained very well controlled even in extreme heat and up steep grades. While the radiator alone is definitely not the entire solution, we believe it is a crucial piece of the puzzle that ultimately solved all our cooling problems. The 13% increase in cooling capacity along with 18% increase in fin area definitely help shed heat faster. If you're having trouble with your JK running hot, we highly recommend you check out our other cooling system mods, and we hope this page answered some of your questions.