Overheating at higher rpm/mph...

2012Rubicon2dr

New member
Overheating at higher rpm/mph started summer 2021 and I have replaced a few parts with no luck. The last thing I have to replace is the water pump, does anyone think that is the issue? All parts are clean with zero mud or debris. Below is the info for my Jeep. Thanks in advance!!!

2012 Rubicon 2dr, Auto trans, 5.13 gears, and 37" tires

Coolant Temps when outside ambient temp is 40°F

~215°F @ Idle ~680rpm
~220°F @ 50mps ~2400rpm
~230°F @ 70mph ~2850rpm
~235°F @ 75mph ~3050rpm
~240°F @ 80mph ~3250rpm

This is what I have changed so far...
Coolant flush (Fall 2021)
Mishimoto 180°F Thermostat (Fall 2021)
AFE BladeRunner GT Series Radiator - 1 3/4" thick core, 75% larger than factory radiator (Fall 2021)
Temperature Sensor (summer 2020)
Thermostat housing (summer 2020)
 

jeeeep

Hooked
had the same issue on my 2010 JKU, would only run hot at higher speeds, found a pinhole in the thermostat housing, replacing that helped a little but issue was solved once I replaced the pump. I could see where the pump had been leaking once I pulled it off.

did you have the radiator pressure tested before you replaced it?
No air in the cooling system?
 

WJCO

Meme King
As TrailHunter mentioned, you can buy a block tester (chemical kit) for about 40 bucks to check that. Also make sure you aren't losing flow through the heater core (you can do this easily at the hoses with a laser/infrared thermometer), but it could be that water pump isn't pumping enough. I can't recall if the 3.6 has a plastic impeller, but sometimes those wear out or break, or the bearing is just starting to seize up.
 

GP NOIR

Hooked
Check to make sure airflow isn’t blocked or diverted. If there’s anything in front of the radiator such as a winch, lights, stinger or grill inserts, air could be blocked or diverted.
 

jeeeep

Hooked
As TrailHunter mentioned, you can buy a block tester (chemical kit) for about 40 bucks to check that. Also make sure you aren't losing flow through the heater core (you can do this easily at the hoses with a laser/infrared thermometer), but it could be that water pump isn't pumping enough. I can't recall if the 3.6 has a plastic impeller, but sometimes those wear out or break, or the bearing is just starting to seize up.
it is a plastic impeller, the one on my JK was cracked but I think the bearing wore out before and I didn't catch the signs.

belt was squeaking but I thought it was due to another cause since it stopped ... um water pump fail
 

2012Rubicon2dr

New member
had the same issue on my 2010 JKU, would only run hot at higher speeds, found a pinhole in the thermostat housing, replacing that helped a little but issue was solved once I replaced the pump. I could see where the pump had been leaking once I pulled it off.

did you have the radiator pressure tested before you replaced it?
No air in the cooling system?
Yes the radiator held pressure and the cooling system was burped with no air. I figured it is the water pump. Thanks!
 

Zeus

Member
Mine will heat up a bit on long uphills but never over heat. Highest I saw was 236 en then the fan kicks in and brings it right down.

Also once I crest the hill it drops down back to normal very quickly.
 

2012Rubicon2dr

New member
Update...
I replaced the water pump (Old WP had cracks in the plastic impellers) and I was still overheating. After further investigation the "Mishimoto 180°F Thermostat" that I replaced in Fall 2021 was stuck closed. I replace the thermostat and everything cools great. Thanks for all the input!!!
 
Been reading a few overhearing threads and this one seems closest to my case.

-2016 JKUR 95,000 mi
-Had CEL P0128 with no symptoms at all.
-Replaced Tstat with MotoRad brand. Bled air.
-Drove an hour up 40 to winter park. Steep switchbacks, high RPMs. Needle never moved above half.
-Over the next week of normal slight grade highway driving, I started to notice the needle creeping up to 3/4 quickly whenever I hit an incline.
-Drove south on 285, more grades, hit 240+ and temp light came on. Never happened before in 8 years. I let off gas and blasted heat and it came right back down.
-Replaced Tstat again with whatever one the dealership had, replaced water pump with OEM (had it in the garage). No signs of damage on the original.
-bled air into a bleed kit funnel 4 times, no change
-No visible signs of leaks

Questions:
-Could the T stat really be bad? I feel the hose coming from the block to the radiator getting hot. That should mean it’s working, right?

-While idling in the driveway for half hour, I get up to 218 degrees or so and the fan never comes on high. Also, I turn the AC on and the fan never comes on high, only the comes on low. Is this normal?
 

WJCO

Meme King
Been reading a few overhearing threads and this one seems closest to my case.

-2016 JKUR 95,000 mi
-Had CEL P0128 with no symptoms at all.
-Replaced Tstat with MotoRad brand. Bled air.
-Drove an hour up 40 to winter park. Steep switchbacks, high RPMs. Needle never moved above half.
-Over the next week of normal slight grade highway driving, I started to notice the needle creeping up to 3/4 quickly whenever I hit an incline.
-Drove south on 285, more grades, hit 240+ and temp light came on. Never happened before in 8 years. I let off gas and blasted heat and it came right back down.
-Replaced Tstat again with whatever one the dealership had, replaced water pump with OEM (had it in the garage). No signs of damage on the original.
-bled air into a bleed kit funnel 4 times, no change
-No visible signs of leaks

Questions:
-Could the T stat really be bad? I feel the hose coming from the block to the radiator getting hot. That should mean it’s working, right?

-While idling in the driveway for half hour, I get up to 218 degrees or so and the fan never comes on high. Also, I turn the AC on and the fan never comes on high, only the comes on low. Is this normal?
Check fan relay and check for mud plugging radiator. Sounds like an air flow problem.
 
Check fan relay and check for mud plugging radiator. Sounds like an air flow problem.

Having trouble figuring out the fan relay.

The TIPM shows a 60amp fuse (which looks fine) and a “rad fan relay lo”. Wouldn’t that only affect the lo fan function?…
 

jeeeep

Hooked
Been reading a few overhearing threads and this one seems closest to my case.

-2016 JKUR 95,000 mi
-Had CEL P0128 with no symptoms at all.
-Replaced Tstat with MotoRad brand. Bled air.
-Drove an hour up 40 to winter park. Steep switchbacks, high RPMs. Needle never moved above half.
-Over the next week of normal slight grade highway driving, I started to notice the needle creeping up to 3/4 quickly whenever I hit an incline.
-Drove south on 285, more grades, hit 240+ and temp light came on. Never happened before in 8 years. I let off gas and blasted heat and it came right back down.
-Replaced Tstat again with whatever one the dealership had, replaced water pump with OEM (had it in the garage). No signs of damage on the original.
-bled air into a bleed kit funnel 4 times, no change
-No visible signs of leaks

Questions:
-Could the T stat really be bad? I feel the hose coming from the block to the radiator getting hot. That should mean it’s working, right?

-While idling in the driveway for half hour, I get up to 218 degrees or so and the fan never comes on high. Also, I turn the AC on and the fan never comes on high, only the comes on low. Is this normal?
old school for checking the Tstat, fill a cooking pot with water, cooking thermostat to keep track of the temps, bring the water to temperature of the Tstat and you can see if it pops open at temp.

If the radiator hoses are stock, check them for soft spots, if they soft that may be collapsing and not allowing full flow, I've found the lower hose tends to be the 1st to fail.

Pull the pump and check the impellers and bearing or do a pressure test on the pump.
 
Believe I found the smoking gun here.

Decided to pull the overflow res while cleaning the fuck out of the radiator and AC condenser fins, and found junk in the bottom.

Looks like oil mixed in. I’m thinking because my oil filter housing was leaking so bad before I swapped it out, that oil mixed with coolant at the warped housing and the block.

My question: Of course a flush is in order.
I’m hesitant to use anything other than water, but should I try and use something stronger to clear the oil buildup? Anyone have experience with this?

IMG_1271.jpeg
 

jeeeep

Hooked
Believe I found the smoking gun here.

Decided to pull the overflow res while cleaning the fuck out of the radiator and AC condenser fins, and found junk in the bottom.

Looks like oil mixed in. I’m thinking because my oil filter housing was leaking so bad before I swapped it out, that oil mixed with coolant at the warped housing and the block.

My question: Of course a flush is in order.
I’m hesitant to use anything other than water, but should I try and use something stronger to clear the oil buildup? Anyone have experience with this?

View attachment 396976
I'd run Dawn dishwashing soap and hot water thru it, won't hurt the system and should flush out the oil.
It'll probably take a good flush to get all the soap foam out but it won't cause any corrosion like chemicals might.
 
I'd run Dawn dishwashing soap and hot water thru it, won't hurt the system and should flush out the oil.
It'll probably take a good flush to get all the soap foam out but it won't cause any corrosion like chemicals might.

I was actually thinking of doing that.
Works for the seals and the ducks when BP spills a couple millions barrels into the ocean right? Oil is oil, right?
 

jeeeep

Hooked
I was actually thinking of doing that.
Works for the seals and the ducks when BP spills a couple millions barrels into the ocean right? Oil is oil, right?
yep, I remember that when my brother-in-law's dad (had a mechanic shop) worked on my Firebird that had a bad head gasket.

He flushed it with dawn and had me keep flushing it with hot soapy water until all the foam was out and the water was clear; I was 17 at the time and it felt like a lifetime of foam lol
 
So I wimped out on soap, not having the patience.

However I did drain and fill with distilled water and BlueDevil radiator flush / degreaser.

Ran it up some steep grades for 45 minutes.
Drained, flushed and refilled with coolant.


Oil buildup in radiator before running degreaser:
IMG_1403.jpeg

Drain after running degreaser (started clear)
IMG_1405.jpeg

Bleeding air from new coolant:
IMG_1408.jpeg

After this, coolant never got above 220 on mild grades / high RPMs, where before it would climb to 230+

However, I ended out finding an OEM thermostat on eBay and couldn’t resist.
I gotta say, I feel like that was the biggest factor.

OEM is quite a bit visibly different (OEM on the right)

IMG_1436.jpeg

Jeep runs between 198 and 208 consistently now. On the highway and around town.

However, coolant temp still reached 231 last weekend climbing 1000 feet in a mile and a half at full push. I topped out so I don’t know if temp would have leveled off or not…I still feel a compression test is in order…
 
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