Coolant running too hot

[phenophlebo]

Just bought a 2018 JK Unlimited Rubicon w/65,000 miles. Appeared to be in great shape and has (almost) brand new 37" tires and what I believe is a 4" lift kit. Overheated on day two after about 50 miles. Back to the dealership and they had it for 7 days. They replaced the thermostat, the water pump & the radiator (all for free, which was cool) but it is STILL overheating. It does better in city driving than on the freeway (which I find strange but I'm no expert) at speeds higher than 70mph. Have to blast the heater and reduce my speed to 60mph and that seems to resolve the problem temporarily. The gauge bounces back and forth but typically rides at about 3/4 and has gone over this for a minute or so on a couple of occasions. Am I missing something? What else could be contributing to this? I heard a rumor (again, I'm no expert) that Jeep JK's have two thermostats? Any ideas that anyone can provide would be truly appreciated. Thank You.

 

[BLACKJKU]

If the air wasn't burped out properly that could be the problem, just because the Dealer did it doesn't mean they know how to do it.

The cooling fan could be the problem, it was found to be the issue before.

read Post #49

Help needed: Jeep suddenly overheating after changing the thermostat

Sometimes it's hard to make repairs over the Internet but we try. Hahaha. I agree.

wranglerjkforum.net

 

[Anybodyhome]

The fact the temp gauge is fluctuating is a prime indicator the cooling loop has air in it. Countless threads in here about properly burping and adding coolant in a case like yours.

1. Put the front end of your Jeep on an incline, like 4-6" higher than the rear. Remove the radiator cap.
2. Add coolant to the radiator a cup or so at a time. Wait for the air bubbles to be forced out the cap opening. Each time the loop "burps" the coolant level will drop in the radiator.
3. Continue to add coolant until the coolant level reaches just below the cap opening and there are no more signs of air bubbles.

Second point I'll bring up is your gearing. With those 37" tires, what is the gearing in your JKU? A JKU lifted 4" with 37s and the proper gearing of a 4.88, 5.13 or 5.38 is not designed to go 70+ down the road. Likewise, if it's under-geared for those 37s, the engine may be working overtime to turn those wheels on the pavement.

 

[NineLives]

My issue was similar after buying a used 2015 JKU last year. Tried everything but the elephant in the room until we couldn't ignore it any longer: the heads/gaskets etc.

However, even after the head repair (which included a new water pump and thermostat), I was still overheating.

I have had quite the ride, so to speak, with thermostats. I'm convinced the MotoRad therms are junk. These therms are OEM and sold at AutoZone and Advance Auto (not sure about O'Reillys or NAPA), and the dealerships usually have a bunch on their shelves too.

I'd verify the part they installed was Genuine Mopar and look for the Chrysler stamp on the part. They may have installed a MotoRad at the dealership. If they did, get a swap for Mopar and test it out. Agree with air pockets too. I'd do it myself after leaving a mechanic, just so I know it's been done.

Good luck!

 

[phenophlebo]

The fact the temp gauge is fluctuating is a prime indicator the cooling loop has air in it. Countless threads in here about properly burping and adding coolant in a case like yours.

1. Put the front end of your Jeep on an incline, like 4-6" higher than the rear. Remove the radiator cap.
2. Add coolant to the radiator a cup or so at a time. Wait for the air bubbles to be forced out the cap opening. Each time the loop "burps" the coolant level will drop in the radiator.
3. Continue to add coolant until the coolant level reaches just below the cap opening and there are no more signs of air bubbles.

Second point I'll bring up is your gearing. With those 37" tires, what is the gearing in your JKU? A JKU lifted 4" with 37s and the proper gearing of a 4.88, 5.13 or 5.38 is not designed to go 70+ down the road. Likewise, if it's under-geared for those 37s, the engine may be working overtime to turn those wheels on the pavement.

Hello Anybodyhome: I thank you for your response and you bring up some great questions that I just don't have the answers for. My brother-in-law (in all truth an auto body guy for 30+ years and knows his way around a car) burped it today because someone else mentioned that just because the dealer performed the repairs doesn't mean they did them correctly. He SAID that he performed it as you described and ended up with coolant all over the shop and ended up replacing at least a gallon and a half of antifreeze when all was said and done. Does this sound right? As far as the gear ratio, that is something I simply don't have the answer to nor do I know how to find it. I purchased the vehicle from the dealer and it is my first jeep and it sure sounds like I didn't perform my due diligence prior to purchase. What I can tell you is that the tires are PRACTICALLY brand new but has uneven wear on the rear tires in the middle of the tire. Obviously the alignment is off but these tires do have signs of wear so someone was driving with them prior to my purchase. This could be why he traded it in however, as he may have encountered the same thing I am now and wanted to get rid of the car. The vehicle does overheat more on the interstate than in city driving which I thought should be the opposite. Idling, stop and go, stop and go, etc, but if the gear ratio is wrong that could account for this, right? Would love any other thoughts you care to share. Thanks again.

 

[phenophlebo]

My issue was similar after buying a used 2015 JKU last year. Tried everything but the elephant in the room until we couldn't ignore it any longer: the heads/gaskets etc.

However, even after the head repair (which included a new water pump and thermostat), I was still overheating.

I have had quite the ride, so to speak, with thermostats. I'm convinced the MotoRad therms are junk. These therms are OEM and sold at AutoZone and Advance Auto (not sure about O'Reillys or NAPA), and the dealerships usually have a bunch on their shelves too.

I'd verify the part they installed was Genuine Mopar and look for the Chrysler stamp on the part. They may have installed a MotoRad at the dealership. If they did, get a swap for Mopar and test it out. Agree with air pockets too. I'd do it myself after leaving a mechanic, just so I know it's been done.

Good luck!

Hey NineLives. They did in fact use a genuine oem Mopar thermostat. Same for the radiator and the water pump. So after all that was it the thermostat that was causing your overheating and did you end up finding a fix?

 

[Speartip]

Hey NineLives. They did in fact use a genuine oem Mopar thermostat. Same for the radiator and the water pump. So after all that was it the thermostat that was causing your overheating and did you end up finding a fix?

Mopar doesn’t make their own thermostats . Probably doesn’t make the rads or water pumps either .
All farmed out to diff manufactures .
I would def burp the system .
Change out stat again . I went threw 3 till it solved my issue .
One of the faulty stats was from a dealer ?
Do a coolant test to see if if possibly head gasket issue .
The cooling systems on the JK’s are really hit & miss.
Some go for 200k without blinking . Others have issues at Hwy speeds .
The 2012-2015 had sand cast issues which constricted coolant flow . That issue was supposedly resolved . But from what I read on here and elsewhere there are still some heat issues .

 

[Anybodyhome]

Hello Anybodyhome: I thank you for your response and you bring up some great questions that I just don't have the answers for. My brother-in-law (in all truth an auto body guy for 30+ years and knows his way around a car) burped it today because someone else mentioned that just because the dealer performed the repairs doesn't mean they did them correctly. He SAID that he performed it as you described and ended up with coolant all over the shop and ended up replacing at least a gallon and a half of antifreeze when all was said and done. Does this sound right? As far as the gear ratio, that is something I simply don't have the answer to nor do I know how to find it. I purchased the vehicle from the dealer and it is my first jeep and it sure sounds like I didn't perform my due diligence prior to purchase. What I can tell you is that the tires are PRACTICALLY brand new but has uneven wear on the rear tires in the middle of the tire. Obviously the alignment is off but these tires do have signs of wear so someone was driving with them prior to my purchase. This could be why he traded it in however, as he may have encountered the same thing I am now and wanted to get rid of the car. The vehicle does overheat more on the interstate than in city driving which I thought should be the opposite. Idling, stop and go, stop and go, etc, but if the gear ratio is wrong that could account for this, right? Would love any other thoughts you care to share. Thanks again.

There are a couple ways to determine the gearing.
First is: enter your VIN at this link and you'll get the build sheet for your JK as it came off the assembly line. That'll tell you which gears it was built with.
https://www.mopar.com/en-us/my-vehicle/vin-lookup.html

Second: on the rear side of the rear differential, there may be a tag showing you the gearing:

The third and final way to determine gearing:

"My brother-in-law (in all truth an auto body guy for 30+ years and knows his way around a car) burped it today because someone else mentioned that just because the dealer performed the repairs doesn't mean they did them correctly. He SAID that he performed it as you described and ended up with coolant all over the shop and ended up replacing at least a gallon and a half of antifreeze when all was said and done. Does this sound right?"

Curious as to how this happened? Was he running the engine at the time? That's about the only way I could imagine spilling coolant all over the place. The engine should not be running. I mean, the radiator burps, the coolant settles and you add a cup or 2 to top off the rad. Repeat the process until no more air burps out the rad.

 

[Danarch]

I’m not sure how much of impact this would have on temps, but has the Jeep been programmed for the 37” tires? If not the shift points will not be correct. Not sure if that really should impact the temp much, other then you may be going a lot faster then you think.

 

[phenophlebo]

I’m not sure how much of impact this would have on temps, but has the Jeep been programmed for the 37” tires? If not the shift points will not be correct. Not sure if that really should impact the temp much, other then you may be going a lot faster then you think.

Good Morning Danarch. You bring up a good point and I was watching YouTube and a couple of videos mentioned that I nee an AEV module that will adjust the shift points to accommodate for the 37" tire size. Like you I don't know if this will impact the temps and I'm wondering if 37s are just too much tire. It certainly appears (obviously I'm no expert.) that (with the proper equipment) 37s should be just fine.

 

[phenophlebo]

There are a couple ways to determine the gearing.
First is: enter your VIN at this link and you'll get the build sheet for your JK as it came off the assembly line. That'll tell you which gears it was built with.
https://www.mopar.com/en-us/my-vehicle/vin-lookup.html

Second: on the rear side of the rear differential, there may be a tag showing you the gearing:
View attachment 124987

The third and final way to determine gearing:

"My brother-in-law (in all truth an auto body guy for 30+ years and knows his way around a car) burped it today because someone else mentioned that just because the dealer performed the repairs doesn't mean they did them correctly. He SAID that he performed it as you described and ended up with coolant all over the shop and ended up replacing at least a gallon and a half of antifreeze when all was said and done. Does this sound right?"

Curious as to how this happened? Was he running the engine at the time? That's about the only way I could imagine spilling coolant all over the place. The engine should not be running. I mean, the radiator burps, the coolant settles and you add a cup or 2 to top off the rad. Repeat the process until no more air burps out the rad.

I did figure out (did a little research) about gear ratio and that tag is missing and I'm particularly set up to count teeth and pinions. I read also that Unlimited Rubicons come standard with 3.21, It's pretty obvious someone did some work on it and I'm 90% certain this is the case. He was blowin all of the air out of the system so this is how he ended up with coolant everywhere. I performed the head gasket test this morning (no milky oil, no air bubbles in the radiator or reservoir, no white exhaust.

 

[Danarch]

You can get Jscan and a OBDII adapter for a lot less the the AEV procal. Again not sure about relationship to temp but wrong gearing, incorrect shift points, and larger tires all have a combination on engine load. It takes money to correctly install a 4” lift and 37” tires, those components affect a lot of different aspects of a Jeep. Guess one reason I’m fine with 2.5”-3” lift and 35” tires.

 

[phenophlebo]

You can get Jscan and a OBDII adapter for a lot less the the AEV procal. Again not sure about relationship to temp but wrong gearing, incorrect shift points, and larger tires all have a combination on engine load. It takes money to correctly install a 4” lift and 37” tires, those components affect a lot of different aspects of a Jeep. Guess one reason I’m fine with 2.5”-3” lift and 35” tires.

Thanks for the info! I was pricing the AEV and it's not terrible but something for less that's just as effective works for me. I agree with you and was wondering if all of the necessary equipment was installed correctly. I was also thinking bout downsizing to 35"s.

 

[phenophlebo]

There are a couple ways to determine the gearing.
First is: enter your VIN at this link and you'll get the build sheet for your JK as it came off the assembly line. That'll tell you which gears it was built with.
https://www.mopar.com/en-us/my-vehicle/vin-lookup.html

Second: on the rear side of the rear differential, there may be a tag showing you the gearing:
View attachment 124987

The third and final way to determine gearing:

"My brother-in-law (in all truth an auto body guy for 30+ years and knows his way around a car) burped it today because someone else mentioned that just because the dealer performed the repairs doesn't mean they did them correctly. He SAID that he performed it as you described and ended up with coolant all over the shop and ended up replacing at least a gallon and a half of antifreeze when all was said and done. Does this sound right?"

Curious as to how this happened? Was he running the engine at the time? That's about the only way I could imagine spilling coolant all over the place. The engine should not be running. I mean, the radiator burps, the coolant settles and you add a cup or 2 to top off the rad. Repeat the process until no more air burps out the rad.

I said 3.21 and I meant 4.10

 

[NineLives]

Mopar doesn’t make their own thermostats . Probably doesn’t make the rads or water pumps either .
All farmed out to diff manufactures .
I would def burp the system .
Change out stat again . I went threw 3 till it solved my issue .
One of the faulty stats was from a dealer ?
Do a coolant test to see if if possibly head gasket issue .
The cooling systems on the JK’s are really hit & miss.
Some go for 200k without blinking . Others have issues at Hwy speeds .
The 2012-2015 had sand cast issues which constricted coolant flow . That issue was supposedly resolved . But from what I read on here and elsewhere there are still some heat issues .

My most recent thermostat has a Chrysler stamp clearly on it, with no other markings. Everything prior clearly said MotoRad on it. Not home to take a pic at the moment.

 

[NineLives]

Hey NineLives. They did in fact use a genuine oem Mopar thermostat. Same for the radiator and the water pump. So after all that was it the thermostat that was causing your overheating and did you end up finding a fix?

My journey was long and painful. Went thru 4 t-stats from October 2022 to May 2023. 1 replaced by a shop, 1 replaced by me, 1 replaced at time of major repair (heads/water pump/timing chain/cam rockers). After the 3rd replacement during the major repairs, I burped myself to make sure it was done right, including bleeder valve. Temps were increasing every time I drove it and the day it hit 257 and red lighted AFTER I'd had $4000 worth of work, I vowed to find a Mopar t-stat. They had been back ordered for a long time. Lucked into finding one at a dealership, installed it myself, burped and bled and I've been fine since. Going on almost 3 months with no temp issues. Oh yeah, between the major repair and the 4th t-stat I also replaced temp sensor.

 

[phenophlebo]

My journey was long and painful. Went thru 4 t-stats from October 2022 to May 2023. 1 replaced by a shop, 1 replaced by me, 1 replaced at time of major repair (heads/water pump/timing chain/cam rockers). After the 3rd replacement during the major repairs, I burped myself to make sure it was done right, including bleeder valve. Temps were increasing every time I drove it and the day it hit 257 and red lighted AFTER I'd had $4000 worth of work, I vowed to find a Mopar t-stat. They had been back ordered for a long time. Lucked into finding one at a dealership, installed it myself, burped and bled and I've been fine since. Going on almost 3 months with no temp issues. Oh yeah, between the major repair and the 4th t-stat I also replaced temp sensor.

Jeez. What a mess but I'm glad you're doing well now. Someone suggested the temp sensor and we were gonna look into that too. Thanks and keep on climbing!

 

[nolefred]

Just bought a 2018 JK Unlimited Rubicon w/65,000 miles. Appeared to be in great shape and has (almost) brand new 37" tires and what I believe is a 4" lift kit. Overheated on day two after about 50 miles. Back to the dealership and they had it for 7 days. They replaced the thermostat, the water pump & the radiator (all for free, which was cool) but it is STILL overheating. It does better in city driving than on the freeway (which I find strange but I'm no expert) at speeds higher than 70mph. Have to blast the heater and reduce my speed to 60mph and that seems to resolve the problem temporarily. The gauge bounces back and forth but typically rides at about 3/4 and has gone over this for a minute or so on a couple of occasions. Am I missing something? What else could be contributing to this? I heard a rumor (again, I'm no expert) that Jeep JK's have two thermostats? Any ideas that anyone can provide would be truly appreciated. Thank You.

I had the EXACT same issue. Replaced engine with a Jasper, two new radiators, two new water pumps, flushed heater core and got a little bit of stuff out of it, and countless thermostats. Finally the mechanic tested the most recent thermostat and voila! It wasn’t opening all the way. This causes a coolant flow issue at higher rpms and on the highway. I can almost guarantee this is your problem. Pull it and stick it in a pot of boiling water and see if it opens all the way. When you see that it doesn’t, test a new one as well. This is a very common problem with these thermostats.

 

[Anybodyhome]

I said 3.21 and I meant 4.10

To be honest, I'm not sure a 4.10 is the best gearing for 37s. A 4.56 minimum will run much more efficiently and a 4.88 will be the sweet spot. Your 4.10 is putting a load on the engine and trans with those 37s.
I'll assume you have an auto trans- here's a chart:

 

[phenophlebo]

To be honest, I'm not sure a 4.10 is the best gearing for 37s. A 4.56 minimum will run much more efficiently and a 4.88 will be the sweet spot. Your 4.10 is putting a load on the engine and trans with those 37s.
I'll assume you have an auto trans- here's a chart:

View attachment 124992

To be honest, I'm not sure a 4.10 is the best gearing for 37s. A 4.56 minimum will run much more efficiently and a 4.88 will be the sweet spot. Your 4.10 is putting a load on the engine and trans with those 37s.
I'll assume you have an auto trans- here's a chart:

View attachment 124992

You are correct. Someone else provided this table and I'm sure it's not at the sweet spot. I told him that I wasn't particularly set up to count teeth and pinions and that the metal plate with the ratio is missing. It's very evident that someone has altered it and that it's not at 4.10 but whatever it's at is still insufficient. Based on the table I was thinking 4.88 would be ideal. Another individual said he experienced the exact same issue and had to replace the thermostat multiple times before finding a solution.

To be honest, I'm not sure a 4.10 is the best gearing for 37s. A 4.56 minimum will run much more efficiently and a 4.88 will be the sweet spot. Your 4.10 is putting a load on the engine and trans with those 37s.
I'll assume you have an auto trans- here's a chart:

View attachment 124992

To be honest, I'm not sure a 4.10 is the best gearing for 37s. A 4.56 minimum will run much more efficiently and a 4.88 will be the sweet spot. Your 4.10 is putting a load on the engine and trans with those 37s.
I'll assume you have an auto trans- here's a chart:

View attachment 124992