High engine temps while going up hills (possible gear issue?)


lulzpwndyah

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So this is something i've searched for and could not find anything like it. I have a 2005 4.0 automatic... the engine is a new Jasper remanufactured engine and the cooling system is almost all new except for the radiator which is the Mopar from what I can tell. The waterpump used was Mopar the thermostat is 195 and the radiator cap is the correct 18 lbs one. I ordered a new radiator cap as a quick and easy test to see if it resolved my issue.

Basically when i'm going up hill on steep grades for example the Grapevine in California on the 5 which is one of the steepest grades for 5 miles in Socal I believe the car begins getting hot... The needle usually stays right below the halfway marker but as I was climbing it went past it and made it to the center of the 0 in the 210 so about 230/5... I have 31 inch duratracs and i'm positive it's stock gearing when i'm climbing at say 50 mph my rpms are below 2k and i'm losing speed with my foot floored. Before I gave up on the climb I got into the furthest right lane and dropped into 2nd and the heat began to drop back to the middle and I climbed the rest of the way up slowly at about 40... Could it be because my gearing was not appropriate therefore making the engine work harder than need be? I also lose speed going down hill without my foot on the gas and my rpms drop to like 1k

When I finally got to my destination I checked under the hood and saw that the overflow reservoir had blown the cap and spilled coolant. I bought some more coolant filled it back up did a few hours of offroading and it did not heat back up...I have about 1k miles on the new engine.

I'm going to check the radiator for cold spots after work but thought that the gearing might be the problem. It's dog shit slow in 3rd i'll be accelerating on the freeway and when I get to 60s I let off to cruise and the rpms drop to 1.8k or 1.9k when I accelerate again it will shoot up to almost 3k and keep on going.
 

freedom_in_4low

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well, 3k is about where you should be on the highway anyway. The 4.0 doesn't like being at 2k or below, at all.

But is it causing your overheating issue? I drove mine for 2 years with stock gearing on 32s and never got past 210 when running a mopar radiator. And that includes mountain passes up to 11,000' where even with 4.56 gears I can't get past 35 mph. But then again, mine is a manual so I can downshift at will and don't try to drive those passes at 1800rpm.
 
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lulzpwndyah

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What I meant by the 3k is that it's accelerating I can't keep a constant speed between 1.8k-3k it's either I cruise at 1.8k or i'm accelerating at 3k but no in between. Those rpms are lost.


Yeah mine is auto unfortunately for this situation.
@Chris do you have any thoughts on this issue?
 

Chris

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That sounds normal to me. If it’s just slightly past the 210, that happens to mine all the time and has happened on every TJ I’ve ever owned.

Hook and an OBDII scanner up to it while driving and see what the actual temperature is. The gauge is only going to be so accurate anyways.
 
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-T.

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When I had something similar happen, it was due to a worn fan clutch. Someone is probably going to jump all over me again today, and say that once the Jeep is moving at highway speeds, the fan clutch shouldn't matter. That's what I thought too, and I replaced a bunch of other items, as I was on a road trip. Everything was fine running down hill or on flat ground, but when the Jeep started climbing, the temp would start climbing again. In the rolling hills of western Iowa, the temps would just keep climbing on the uphills until at 230 degrees, I'd pull off the road and let it cool down. First, I stopped and changed the thermostat and got back on the highway. This had no effect. Then, I found a NAPA that had a radiator in stock, so I stopped and replaced the radiator in the parking lot. Back on the road, and the situation was the same. So, at that point, the clutch was the only thing that wasn't new or at least close to new (water pump and hoses were changed before the trip) I picked up a fan clutch at another NAPA along the route, and replaced it in a Subway parking lot. All of the overheating issues were gone for the remainder of the 4000 mile trip. And I have never had temperature problems since (2017) All this time, I assumed the fan clutch was for low speed stuff, but it helps on the highway as well.

Also, since this crazy event, I watch the temps pretty obsessively on long trips via an OBD reader and Torque app on my phone, and I have found that when climbing really steep inclines on the highway, the Jeep will run cooler when it is spinning the fan faster, so the additional engine RPM doesn't create more heat than lugging the engine with fan spinning slowly. So, on longer climbs, I've watched the temps start to climb - nothing serious, but it will start heading toward 220. Then the transmission will drop a gear, the RPMs jump up and the temps immediately begin to come down. I will run the poor engine hard climbing out of Denver, running 50 mph in 2nd gear, but it honestly runs nice and cool doing this. Counter intuitive, but it seems keeping that fan spinning really makes a difference.

So, I'd first make sure the fan clutch is good. Replace if needed - I have found that the HD fans make a lot more noise and don't improve things much. I've had better luck with a good non-HD fan clutch even though they seem to cost a bit more. Then make sure you are dropping the Jeep out of OD just as you start to climb, using the switch on the dash, rather than waiting for the computer to do it, and see if that helps. If all else fails, get in the right lane and drop to second and let it roar.
 
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freedom_in_4low

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So, at that point, the clutch was the only thing that wasn't new or at least close to new (water pump and hoses were changed before the trip) I picked up a fan clutch at another NAPA along the route, and replaced it in a Subway parking lot. All of the overheating issues were gone for the remainder of the 4000 mile trip. And I have never had temperature problems since (2017) All this time, I assumed the fan clutch was for low speed stuff, but it helps on the highway as well.

Did you look at the fan clutch when you took it out? Do you think it was freewheeling when it should have been locked, or locked when it should have been free?

I've seen rumors of this phenomenon before but haven't ever been able to wrap my head around how it happens.

Just spitballing here. Fluid flow is complicated. The best I can come up with is if the fan is locked when it should be freewheeling, and the engine is causing it to spin at a slower rate than it would be if it were freewheeling, then it basically becomes an airflow obstruction. To throw a little shop talk in (I'm an HVAC engineer), the heat transfer of a heat exchanger doesn't really improve much past about 1500ft/min. That's less than 20mph, so there's really no need for a fan beyond there. The only reason a fan clutch could have any impact at all at highway speed would be if it's doing something funny that's creating a stagnation effect at the radiator. Fans do funny things when you play with their inlet and outlet pressure relationship.
 
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Steel City 06

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Going somewhat over 210/midpoint is normal. If it reaches the 3/4 point, you have a problem.

Don't be afraid to rev the engine. You are more likely to overheat and damage (by lugging) the engine at low RPM than you are by redlining it. I routinely run mine up to redline while accelerating and hold 4500+ when climbing steep hills. (Depending upon your gearing, this may or may not be feasible.)
 
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lulzpwndyah

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Hey guys, so I checked the fan clutch and it looked good... I think... I grabbed the fan and tried to spin it but it only spun maybe half a turn but probably less.. I touched the radiator after a good spirited drive through the front in between the grille and actually found some cold spots down near the bottom of the radiator... The top was ridiculously hot. I'm guessing I need a new radiator as it doesn't seem to be absorbing the heat evenly throughout the whole thing. but i'm unsure is it normal for the top to be dog hot after drives?

On the subject of climbing uphill I tried to get my engine to rev more but it just would not, I had my foot all the way in and it was around 2k I only went upto 4.5k rpms when I dropped gears.
 

pagrey

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1/2 turn is a bad fan clutch in my opinion, that is way too much even cold.

Edit: just to clarify when I shove my fan blade with a good firm push on a cold engine the blade travels less than 6" from where I release it
 
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lulzpwndyah

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okay I wasn't sure if it had to move some or not but half was an exaggeration. I plan on changing the radiator soon... maybe this weekend... is the fan clutch very difficult or can it be done easily while the radiator is off.... I have an autoimmune disease so it makes it harder for me to wrench on my Jeep... I still enjoy working on it but I work slower and take more breaks than most people do because I get tired or in pain quickly.
 

pagrey

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Do the clutch first. Radiators very rarely go bad without popping on top. The clutch is fairly easy, you just have to have the correct size wrench and it spins off after you unbolt the fan. You don't have to pull the radiator.
 
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Jerry Bransford

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Bad fan clutches cause overheating at idle or slow speeds like crawling offroad or in stop & go traffic. At cruising speeds 60-70 mph airflow through the radiator is what does the cooling.

At speed on the highway it's either a bad radiator or, my first thought, your engine is simply struggling in the situation you described. Shut your Overdrive off when making climbs so the engine is operating at a more efficient rpm which also spins the fan faster. 2K rpms is simply too low of a cruising rpm and it's especially too low to be climbing grades at. Yes my daily driver and my wife's daily driver cars both easily do that at 2k rpms but they're not turning big tires and they're not even close to being as heavy as a TJ is.

The stock 3.73 ratio isn't helping either. Your 42RLE's Overdrive ratio is .69 which is REALLY excessive it drops the RPMs too much. Regearing both axles to a lower ratio would help everything, even your mpg.
 
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lulzpwndyah

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@Jerry Bransford okay I thought it might be the radiator just based on finding cold spots after a long drive... I also thought it was possibly struggling to climb which could cause over exertion and cause it to heat up... i'm guessing from what i've read to resolve my low rpms issue i'll have to regear my diff.... and if i'm right about the regear fixing the low cruising rpm i'm guessing i'd have to go with something like 4.88 gears correct?
 
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lulzpwndyah

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Okay, I actually figured out how it works this time. I had tried other times but was always distracted.

I have planned on staying on 31s for the next year or two but many people tell me my suspension i've ordered is overkill for 31s and I should go to 33s or 35s so maybe 33s in the next year.

Based off numbers I plugged in I believe I have 3.07 gears atm
 

Steel City 06

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The deepest you can go with non-Rubicon axles is 5.13. 5.13 would be ideal for 33s and acceptable for 31s or 35s. Ideally with 35s you would go to 5.38, but 5.13 is the deepest you can go without an axle swap.

If you think you’ll end up with 33s or larger, go 5.13. That way you’re future proofed. In the meantime you would just be very slightly over the RPM target.
 
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lulzpwndyah

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The deepest you can go with non-Rubicon axles is 5.13. 5.13 would be ideal for 33s and acceptable for 31s or 35s. Ideally with 35s you would go to 5.38, but 5.13 is the deepest you can go without an axle swap.

If you think you’ll end up with 33s or larger, go 5.13. That way you’re future proofed. In the meantime you would just be very slightly over the RPM target.

Got it okay and 5.13 is still acceptable for highway driving? I drive far on the weekends during the week I drive less than 10 miles to work.

Right now my mechanic is looking for 2 Dana 44 housings to swap out my axles if the price is right... otherwise I will go with chromly axles upfront on the Dana 30 and upgrade the rear to super dana 35.
 

Steel City 06

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Got it okay and 5.13 is still acceptable for highway driving? I drive far on the weekends during the week I drive less than 10 miles to work.

Right now my mechanic is looking for 2 Dana 44 housings to swap out my axles if the price is right... otherwise I will go with chromly axles upfront on the Dana 30 and upgrade the rear to super dana 35.
With 33s it would be perfect for highway driving. With 31s it would still be quite reasonable, just a little bit of extra torque, a slight amount of extra noise, and a likely imperceptibly small loss of fuel economy. Many of the manual TJ owners target about 3000 RPM at 75 mph, which that gearing would get you very close to with 31s. With 33s, you would be at about 2600 RPM at 70, which is ideal for the autos.

Most of the ratio advice on this site is based on highway speeds. If you were building a trail-only rig, the suggestion would probably be to go as deep as possible.