So I have a 15 jk, I have been having some trouble with my the engine running hot. My coolant temp will get all the way up to 240s (3/4 on temp gauge) before fan kicks on and it takes it down to low 200s. After it takes it down it will baseline around 222 and uphill slops will take it up to 230. I’m running a 6in lift with 37/13.50s on Dana 30 in front and 44 in rear (just hit 100k miles) This temp is interstate driving 65-80ish mph, I'm in 5th gear most of the time but shifting to 6th doesn’t help with the temp any. Thermostat went bad and was replaced 15-20k miles ago and I just replaced a leaking oil cooler. Still having this issue. Any help would be greatly appreciated!
2015 Jeep JK overheating
- Thread starter TyLawson410
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- coolant temp help overheating
Have you re-geared? If not, you're operating your engine in a low rpm/high load map running down the highway. Lower engine rpm also means lower water pump flow. This all equates to higher heat soak. 6th not helping makes since as it puts the engine into an even lower rpm.
If all was fine before the t-stat swap then it may be a low quality stat that is not functioning quickly enough. Replace with OEM or equivalent and give that a try. You should also be sure all the air is burped from the coolant system...
For one thing, if you're running 37's with the stock gears, you're way off. If you've got a Rubicon you've got 4.10:1 gears. But since you've got a D30 in the front, it's not a Rubicon, which means you have (at best) a 3.73:1 gear. You need to be at 5.13:1 or, better yet, 5.38.
Your 222F engine temp is totally normal. But your engine is way out of the power band and working FAR too hard, so it's no surprise that mild slopes (which are all the interstates are allowed to have) causes it to overheat. The fact that you cannot use your overdrive gear is further evidence that your gearing is a mess. Shifting into 6th won't help because it means your gearing is even further off and the poor engine is working even harder.
Your thermostat could certainly have failed prematurely, but replacing it will not really help unless you fix the real problem.
Your 222F engine temp is totally normal. But your engine is way out of the power band and working FAR too hard, so it's no surprise that mild slopes (which are all the interstates are allowed to have) causes it to overheat. The fact that you cannot use your overdrive gear is further evidence that your gearing is a mess. Shifting into 6th won't help because it means your gearing is even further off and the poor engine is working even harder.
Your thermostat could certainly have failed prematurely, but replacing it will not really help unless you fix the real problem.
It’s not a rubicon, just a sport and stock gearing. I’m planning on do 60 swaps for both the front and rear closer towards August-September. If the gearing is the issue would it even be worth it to re gear at this point if I’m swapping them in 6ish or so months? The thermostat was replaced at a dealership (I was on a road trip and couldn’t swap it myself) so I assume they used an oem part. I haven’t noticed this issue before recently. I’m running about 3-3.5 rpm’s when this is happening. I can take a video of my dash cluster if this would help
Probably not. I'd probably try to move up the swap (and make sure the D60 has the right gearing).
The only thing replacing it with an OEM part guarantees is that you'll pay more for the part. They buy the same one you can, slap a label on it, and add a premium to the price. It could still have failed. All manufacturers produce duds once in a while.
So do I need to just keep and eye on the temp and try to let off or gear down the keep the temp down until I can swap them? What gearing would you recommend for the 60s? Also a dumb question, after replacing my cooler I was under my Jeep checking everything else and making sure the leak has stopped I noticed my drive shaft seal has blown so I have a new one on the way, would this contribute to any of the issues I have?
The axles don't have any impact on gear ratios. You're still going to want 5.38's.
I don't think so, no.
Rear, from the t-case? Depending on how long it's been going on... Probably not significant enough though.
Before you drop a chunk of change on the new axles..... get your machine re-geared before you break something serious. Here are gearing charts for the 3.6 both auto and manual transmissions that show you where your rear end needs to be:
I'm going to disagree. They're running 37" tires on a Dana 30. That's too much tire for that little twig of an axle. Regearing is a good idea, but axles strong enough to handle the abuse are an even better idea.
Did you even recalibrate your speedometer when putting the bigger tires on?
Lckydrw
New Member
Same problem on 35s with 3.21s. I tested this theory by running my engine at my desired RPM on the gear chart by controlling when I shift.
IE my setup with 4.56 shows my RPMs at 2350 instead of my current 1800 at 70mph with my auto transmission. Which is where my 4th gear keeps my RPMs now. Rode around in 4th…engine temps remain normal. Confirmed Regear needed.
Too much work with not enough coolant circulating.