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Old 03-25-2019, 09:40 AM
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JKU Engine Overheating

I have a 2017 JKU that recently underwent lift/regear. I run 35s on a 3.5Ē lift and 4.56 gear ratio. I put on steel front/rear bumpers and sliders. Today I was driving uphill on freeway about 75-80 mph on a 7% grade for about 3 miles with A/C on. At the top of the climb my temperature light went off and I pulled to the side. Let the Jeep cool for 20 minutes and checked fluid levels/fan. Drove home another 40 miles with no issues and temp range between 203-231. Engine coolant half full, radiator level totally full, fan works, no leaks, and no mud caked on the radiator. Put a winch on two months ago and havenít had issues off-road or on similar grade ascents until today. I am hoping itís a one off event due to combo of A/C and uphill grade - but I would think I should have no trouble with 7% grade on an 80 degree day. Any thoughts or ideas?

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Old 03-25-2019, 10:40 AM   #2
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T-stat?
You'll have to keep a watchful eye for a while.
My t-stat failed but failed in the open position.

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Old 03-25-2019, 11:09 AM   #3
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Sorry to say that is pretty normal for a 3.6 JK. 203-240 temps are a regular occurrence and my JK overheats pretty much every time I go off road. Computer will turn on the fan at 226F. But it will not be able to keep up with cooling. So this is a sad reality of a 3.6 in a jk. There is a lot of threads on this problem and what can be done and the general consensus is not much. Some have tweaked the programming with software, not just a programmer will do it!, some have upgraded the radiator.

I am sure what you will get with this thread is a bunch of people saying it isn't normal, that is because the don't know their JK does this, mostly because the temp needle doesn't move from center until over 235. But otherwise the rest that aren't aware is because there isn't 7% grade that last long enough to overcome the ability of the fan. In Colorado I see temps in the 240s regularly and as I said I overheat every time I off road.
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Old 03-25-2019, 11:13 AM   #4
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Sorry to say that is pretty normal for a 3.6 JK. 203-240 temps are a regular occurrence and my JK overheats pretty much every time I go off road. Computer will turn on the fan at 226F. But it will not be able to keep up with cooling. So this is a sad reality of a 3.6 in a jk. There is a lot of threads on this problem and what can be done and the general consensus is not much. Some have tweaked the programming with software, not just a programmer will do it!, some have upgraded the radiator.

I am sure what you will get with this thread is a bunch of people saying it isn't normal, that is because the don't know their JK does this, mostly because the temp needle doesn't move from center until over 235. But otherwise the rest that aren't aware is because there isn't 7% grade that last long enough to overcome the ability of the fan. In Colorado I see temps in the 240s regularly and as I said I overheat every time I off road.
I've never dinged the temp idiot bell even pulling my overweight teardrop up hills with 3.73s/33s manual trans. I've hit 230 degrees but never higher.
I've got about 126,000 miles on the mill and have R&R'd the coolant once.
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Old 03-25-2019, 11:33 AM   #5
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I've never dinged the temp idiot bell even pulling my overweight teardrop up hills with 3.73s/33s manual trans. I've hit 230 degrees but never higher.
I've got about 126,000 miles on the mill and have R&R'd the coolant once.
I have only gotten the warning 5 times or so, so not too bad. But I know it happens so I EIVC to Coolant when in 4LO or headed to the high county, which I am going to guess you don't have, and as soon as I see 235, I back off. The temp needle never moves... I know how to handle it now.
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Old 03-25-2019, 11:46 AM   #6
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Is it the hot oil warning with the small red light?
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Old 03-25-2019, 11:56 AM
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Thanks for your responses. Iíve been doing more research and it does sound common - which is unfortunate. I plan to monitor the temp closely and see if the issues persists. Maybe I will keep the A/C on low just to engage the fan prior to hitting 226 degree where it turns on automatically. A lot of added weight plus +3000k on long/steep ascent could have just overdone it. Will be more careful going forward.

No hot oil light. Just temp warning light. Didnít get a read on what the temp actually was at that time - too busy trying to pull over on the freeway!
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Old 03-25-2019, 12:20 PM   #8
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Thanks for your responses. Iíve been doing more research and it does sound common - which is unfortunate. I plan to monitor the temp closely and see if the issues persists. Maybe I will keep the A/C on low just to engage the fan prior to hitting 226 degree where it turns on automatically. A lot of added weight plus +3000k on long/steep ascent could have just overdone it. Will be more careful going forward.

No hot oil light. Just temp warning light. Didnít get a read on what the temp actually was at that time - too busy trying to pull over on the freeway!
The condition seems common. The tire wheel combo is probably not helping either. Your thermostat could be lazy, I would check into that. I would also turn the AC on, and blow maximum heat through the unit, not cold air. The heater core acts as a small radiator, and turning the blower onto max heat will drop coolant temperature a bid faster. Turning on AC will also force the radiator cooling fan to run, although once the engine hits 226F the fan comes on with or without the AC running.
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Old 03-25-2019, 03:14 PM   #9
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When I pull the teardrop through the co mountains, I have the heat on high and all the windows down. The heater works great to cool down the engine a bit but sure does warm up the cab.
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Old 03-25-2019, 09:54 PM   #10
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Where is your winch mounted - is it in front of radiator? Do you have those grill insert or angry grill things? Both would be blocking flow of cooling air when you need it most.
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Old 03-25-2019, 10:22 PM   #11
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Check to see if your radiator fins are plugged up with mud, bugs, etc. That will really hinder your cooling system and lead to hot temps.
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Old 03-25-2019, 11:24 PM   #12
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Sorry to say that is pretty normal for a 3.6 JK. 203-240 temps are a regular occurrence and my JK overheats pretty much every time I go off road. Computer will turn on the fan at 226F. But it will not be able to keep up with cooling. So this is a sad reality of a 3.6 in a jk. There is a lot of threads on this problem and what can be done and the general consensus is not much. Some have tweaked the programming with software, not just a programmer will do it!, some have upgraded the radiator.

I am sure what you will get with this thread is a bunch of people saying it isn't normal, that is because the don't know their JK does this, mostly because the temp needle doesn't move from center until over 235. But otherwise the rest that aren't aware is because there isn't 7% grade that last long enough to overcome the ability of the fan. In Colorado I see temps in the 240s regularly and as I said I overheat every time I off road.
This is exactly right. As someone else mentioned, turning the heater on will cool it off pretty well, at the expense of your comfort.

BTW, I'm one of those who's changed both the fan start temp and upgraded the radiator. I won't know till the weather warms up and I head to the mountains again whether the upgraded radiator was worthwhile.

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Old 03-26-2019, 02:03 PM
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Yes - the winch is mounted on top of front bumper and I do have grill inserts. This setup has been in place since January and I had no issues until last weekend. I did a few off-road trips in Big Bear and J Tree with some significant elevation gain. Although temps in SoCal were a bit cooler at that time then.

I checked the radiator and saw no mud build up.
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Old 03-26-2019, 02:06 PM   #14
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Ditch the grill inserts, for sure. They are just decoration, and serve no useful purpose.

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Old 03-26-2019, 03:48 PM   #15
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With already restrictive and poor flow your winch and bumper won't help. I would absolutely ditch the grill inserts or look for a slimmer design.
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Old 03-26-2019, 04:09 PM   #16
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If you have concern about engine temp, the winch needs a bumper that mounts it low between frame rails - and grill inserts do nothing but block air flow.
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Old 03-26-2019, 04:13 PM   #17
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If you have concern about engine temp, the winch needs a bumper that mounts it low between frame rails - and grill inserts do nothing but block air flow.
^^^X2, plus, I don't see a air dam. These are all contributors to higher coolant temperatures.

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Old 03-26-2019, 04:47 PM   #18
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If you have concern about engine temp, the winch needs a bumper that mounts it low between frame rails - and grill inserts do nothing but block air flow.
That's true, but mine is buried in the bumper and it'll still get hot on tall passes. Lowering the winch is worth doing, but is unlikely to make coolant temps drop meaningfully, by itself.

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Old 03-26-2019, 05:51 PM   #19
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That's true, but mine is buried in the bumper and it'll still get hot on tall passes. Lowering the winch is worth doing, but is unlikely to make coolant temps drop meaningfully, by itself.

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Yep, my which sits between the frame rails as well. I still get hot on steep grades. I just know that as I approach the grade, windows go down and heat goes on high.
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Old 03-27-2019, 06:22 PM
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I am going to take out grill inserts. As of now my options are limited with the winch mount. I am going off-roading this weekend. This trail involves some very steep climbs. I did it recently with no issues. I will monitor temps and let you know. Will employ A/C fan and blast heat if needed.

I tested on the freeway today and my highway temp is about 221-224F, high of 228 (up inclines) going 70 mph. High heat & A/C fan brought it down to average 217-219F, and low of 212F. I’d say it provides about 6-8 degrees of relief on average. Hopefully it will improve further after taking out grill inserts.
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Old 03-27-2019, 09:45 PM   #21
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Hmm, I've hammered up some long grades in high temps at high revs and with A/C, like Towne Pass in Death Valley, without any signs of problems. Although I don't pull trailers, I have done it with a full load of passengers and gear. No problems off road in the heat either. I don't have anything restricting my airflow though, no grill inserts and my winch/bumper are low.
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Old 03-27-2019, 11:10 PM   #22
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Haven't done a test yet but I believe that removing the air dam is a big contributing factor to hot Jk's. The air dam creates a low pressure area that helps pull air through the radiator. Look at the number of vehicles that have some form of air dam. All below the radiator. When you drive at speed that forces the air to the side or down creating a low pressure area that the air flowing through the radiator fills. That gives increased air flow through the radiator and therefore better cooling.
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Old 03-28-2019, 05:26 AM   #23
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Get rid of the grill inserts.

You can add hood vents that will also help.

You can also add a product like Water Wetter to your coolant that is supposed to reduce operating temps.

When it gets hot turn off the A/C and turn on your heater full blast.
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Old 03-29-2019, 08:58 PM   #24
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Mine will creep up to 3/4 on grades so I removed my grill inserts. No change in temps.

I too have a higher.mounted winch (VR10K on a PSC brawler lite).

Since it's never put me onto limp mode I just deal with mine as is. Brought it in to the dealer with heat complaints and they found the passenger head running 60* hotter than the driver side. Replaced both heads, no change.
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Old 03-29-2019, 09:27 PM   #25
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and grill inserts do nothing but block air flow.
Almost all vehicles on the road have a grille/ covering on them. If they blocked that much air, manufactures wouldn't put them there.
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Old 03-29-2019, 09:28 PM   #26
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Ditch the grill inserts, for sure. They are just decoration, and serve no useful purpose.

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Keep rocks and other debris from hitting your radiator is not a useful purpose?
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Old 03-29-2019, 09:42 PM   #27
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Not with the radiator sitting behind the AC condenser and transmission cooler, no.

They are just ornaments masquerading as useful.

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Old 03-29-2019, 10:06 PM   #28
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Haven't done a test yet but I believe that removing the air dam is a big contributing factor to hot Jk's. The air dam creates a low pressure area that helps pull air through the radiator. Look at the number of vehicles that have some form of air dam. All below the radiator. When you drive at speed that forces the air to the side or down creating a low pressure area that the air flowing through the radiator fills. That gives increased air flow through the radiator and therefore better cooling.
^^^Bingo..many don't understand this. Also remove your engine cover, and keep your radiator flushed out externally.

I live in hot as hell Phoenix az. And do not run these high coolant temperatures that many of you have mentioned. Plus I do drive in our mountain areas, but do not tow trailers.
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Old 03-29-2019, 10:20 PM   #29
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2014 Rubicon w/4.10, 34" tires and a winch dead in front of the grill... I live in Arizona and have never overheated on or off-road, and even use the A/C off road in some circumstances. I'm not 'unaware of it', it simply doesn't overheat (on warm days I usually monitor coolant and trans temp when off road.) I do see temps in the 220-225 range but that's because the JK doesn't turn the fan on until these temps (or at least doesn't spin it fast enough to hear, it's variable-speed.) But once the fan comes on coolant temp is controlled.

That's not to say that it's impossible to overheat, just that it doesn't happen to me (and apparently several others in the thread) and if I overheated every time I went offroad personally I'd be looking for a problem, and in the OP's case (overheated on a 80F day and then everything seemed normal) I'd probably be checking the thermostat because yes, the prediction above was right, I'm saying that common severe overheating of a JK cooling system in good working order is not normal.
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Old 03-30-2019, 12:02 AM   #30
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I wish I could find a jk in my area that didn’t overheat. I would like to see what they are doing different. Every 3.6 jk I have been in, that is a half dozen, has seen 235-245 temps off road or on long uphills. Then on here people say that theirs doesn’t. I am around 3 jkurs in hunting season every year, so not during high temp times. Every one of them the temp needle starts to climb in 4lo driving into a back country spot And every one of them I can hear the fan kick on when we stop to glass an area and leave it running. So that is 226 just sitting still at an air temp in the 40’s. My fan turns on in stop a go traffic when it is single digits temp out side. Gauge doesn’t budge until 235. So if you see anything other than dead nuts center you are 10 degrees from a warning. I would be surprised if everyone says they haven’t needle seen the needle go past center. To me 235-240 is overheating. Any time the fan is over come in cooling capability and you have to alter what you are doing that is overheating. Maybe what others are saying is limp mode or a CEL indicates over heating and that is the difference.

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