Replace Thermostat Jeep Wrangler 2012-2017
Article by Mark Trotta
Replacing the thermostat on your 3.6L Wrangler JK involves removing the air intake hose, draining coolant, taking the lower radiator hose off the engine, and installing the new thermostat. Once done, refill with proper coolant and purge the system of air pockets (more about that at end of article).
Engine Code P0128
Shortly before turning 67k miles, the check engine light on my 2016 Wrangler came on. A quick scan showed code P0128 - "coolant temp below regulating temperature".
After checking that the coolant level was not low, I ordered a Mahle OEM replacement thermostat.
NOTE: On 2012 and up Jeeps, the thermostat is sealed in a plastic housing assembly, so you must replace the entire unit.
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Caution: Never attempt this repair while the engine is hot.
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Getting Started
Loosen air intake clamps and remove intake tube.
The clamp nuts on my AFE Air Box took a 7/16" socket. Factory air box clamp bolts may be metric.
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There is an air temp sensor underneath the air intake tube.
I was able to place the intake tube up and out of the way without disconnecting the pigtail socket.
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Drain Coolant
To drain the coolant and replace the thermostat, there is no need to raise a Jeep with a 3" or higher lift.
On the bottom passenger-side of the radiator, there is a plastic drain valve. To access it, you may have to remove the splash shield retainers with a trim tool.
Clogged Drain Valve
After turning the drain valve counter-clockwise with a pair of pliers, nothing came out!
I had the radiator cap off, so I could see there was plenty of fluid.
Turns out this is not so uncommon; a little sludge buildup prevents coolant from draining.
Rather than mess around with the plastic plug, I went to Plan B - disconnect the lower radiator hose at the engine.
First I had to remove the heater hose in front of it, which released quite a bit of coolant by itself.
Have a drain pan ready!
Before pulling the lower hose off the outlet, cut off the twist-tie holding the hose to the radiator support.
NOTE: If you're not flushing the entire coolant system, you don't need to drain all the fluid, just enough so that the thermostat inlet is not full of coolant. In fact, the less you take out, the easier it will be to refill and get the air pockets out.
Tools Needed
Pictured left to right; Inch/Pounds torque wrench, 1/4 drive ratchet, 1/4 drive nut driver with 10mm socket, slip-joint pliers, hose clamp pliers, 7" Channel-locks, wire snips, picker outer tool.
You'll also need a drain pan (to hold at least 6 quarts) and a funnel.
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Remove Old Thermostat Housing
Once the obstructions are out of the way, the thermostat removes with two 10mm fasteners.
A cordless magnetic swivel flashlight comes in handy.
Make sure that the old gasket is not still sticking to inlet before installing new unit!
Once the old gasket is removed, clean mating areas with a shop towel and brake parts cleaner.
Install New Thermostat Assembly
Mahle Ti23695 is the OEM thermostat for 2012-2017 Wranglers and several other Jeep/Mopar years and models.
The replacement Mahle unit comes with a new gasket already attached.
Factory torque on thermostat bolts is 105 to 106 inch/pounds.
Here, I'm using a 1/4 drive Inch-Pounds torque wrench.
After re-installing the hoses, a new zip-tie was installed to hold the lower hose to the radiator support.
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Correct Coolant is O.A.T.
The correct coolant for 2013-up Jeeps is known as OAT (Organic Acid Technology).
The Mopar part number is 68163849AC and is rated for 10 years or 150,000 miles. When brand new, it is purple in color, but fades to pink/red/orange over time.
CAUTION: Do Not mix OAT with any other coolant, including HOAT (Hybrid Organic Acid Technology), which is used in earlier Jeeps and Mopars.
Is Burping The Coolant System Necessary?
There are several ways to purge the system of unwanted air pockets.
What I did was, with the engine idling, slowly poured coolant back into the radiator until full, then put the heat on the highest setting. With the motor running I watched for air bubbles (about 10 minutes), adding coolant as needed.
TIP: Squeezing the upper hose a few times will help push stubborn air pockets out.
After the coolant level in the radiator leveled off, I filled up the overflow reservoir half-way and reinstalled the radiator cap.
If you can let the Jeep sit overnight, pockets of trapped air will naturally rise to the top of the cooling system. In the morning, you'll notice that the once-full coolant level is now low (air escaped).
NOTE: There is a bleed screw on top of OE-style thermostat housings, but I didn't need to use it.
Another way to purge air pockets is to park on an incline. By elevating the front of the Jeep, the radiator neck is now the highest point of the cooling system.
How Do I Know All Air Bubbles Are Out Of Cooling System?
When your interior vents blow consistently hot air, and the coolant level stops dropping, and the temperature gauge stays steady at normal operating range, all the air is out of the system.
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Road Test
After re-checking the coolant level (with engine cold), I did a five-mile road test. With the engine warmed up, coolant temp needle pointed straight up (half-way mark) same as it always did. The Jeep ran fine, just as it always did.
Heat blows hot, A/C blows cold. All is good.
The final step was clearing the 'check engine light' with a scan tool.
Notes and Misc
According to internet sources, average shop cost for a 2012-2017 Jeep Wrangler thermostat replacement is between $350 and $550. So congratulate yourself for saving some money (now clean up the mess you made).
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