High temps and cruise

[jriggsaz]

I previously had a 3.6L JK and with the cruise control set, it would downshift and rev out to maintain speed when pulling hills. My JL with 33k miles is TERRIBLE in these same scenarios. I can hit those same hills with the cruise set at 75 mph and the Jeep will drop all the way down to 55 mph before dropping from 8th to 7th gear. I would have thought that with an 8 spd transmission it would slowly downshift to maintain RPM's but it refuses to do so.

I can manually downshift but my coolant temps immediately jump from about 215 to 240+. These coolant temps occur regardless of the ambient air temp.

I'm concerned about how easily I can hit ECTs of 240+, even if I'm not pushing the Jeep very hard.

Between my GFC RTT and cargo, I've probably added 1000 lbs of payload which shouldn't be that big of a problem for the Jeep. I'm on 38's with 4.56 gears so my final drive ratio is slightly lower than stock, but again, that alone shouldn't affect the Jeep that much.

I've searched the forums and haven't seen much related to the cruise control issue. I'd welcome your feedback on that and the high coolant temps that I'm seeing.

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[grimmjeeper]

Have you programmed the gears and tires into the computer?

Mine on 37s downshifts just fine and has no problem maintaining speed.

Mabe disconnect both batteries for a bit so the transmission is forced to relearn.

Also, don't worry about coolant temps in the 240s. These modern diesels are designed specifically to run at those temps on purpose. You're not going to damage the engine like you would a 30 year old gas engine.

I would only worry about temperatures when the engine starts to derate on you.

 

[jriggsaz]

Yeah, I have the tires and gears programmed via my Tazer. I've also replaced both batteries on the Jeep and haven't seen any changes in the behavior of the transmission.

I just got back from an AZ to CO trip with a newly installed Banks Derringer and I didn't notice any improvement in these issues that I mentioned. I did notice an increase in power on level 6, but that was about it.

 

[BaconFury]

I would un-marry and then re-marry your tazer. After that go through and make sure your gears and tires still have the correct selection. Many things are often fixed via the un-marry/re-marry.

 

[ChuckQue]

That doesn’t seem right. We just did a 600 mile trip with lots of long hill climbs with cruise control set and never had a problem with shifts or whatnot. While I’m not on 38’s, I’m on heavy 35’s, beadlocks, armored up, light bar, and we had the Jeep packed full including fridge, tools, luggage, cases of wine, etc lol. I only saw oil temps of 230’s a few times and just turned the fan to high via Tazer which dropped the temps into the 220’s.

 

[Ratbert]

Mine is stupidly heavy, 37s, and 4.63 gears. Cruise (adaptive) holds fairly well through the Rockies, where "fairly well" is that it's very rare that I need to help it out by stepping on the pedal. It definitely doesn't drop in speed like you're experiencing.

 

[zouch]

with 37s and 4.56s, mine shifts and maintains set speeds just fine.

Coolant temps can quickly approach what you describe when cruising ~70+ on climbs at altitude in near-triple-digit ambient temps, but everything still works as intended. (i still plan to put an aluminum radiator in at the first excuse.)

def sounds like something is amiss there; probably something basic.
please keep us posted with what you find.

 

[Plongson]

I've posted this before but it is probably good to push it out there once and a while.
It came directly from a MOPAR engineer when I was corresponding about heat issues with them a while back.

I'm old school and still don't like this high temp. On top of that, when ambient is above 80°f, the coolant temp will climb FAST...

 

[Old Jeeper]

I previously had a 3.6L JK and with the cruise control set, it would downshift and rev out to maintain speed when pulling hills. My JL with 33k miles is TERRIBLE in these same scenarios. I can hit those same hills with the cruise set at 75 mph and the Jeep will drop all the way down to 55 mph before dropping from 8th to 7th gear. I would have thought that with an 8 spd transmission it would slowly downshift to maintain RPM's but it refuses to do so.

I can manually downshift but my coolant temps immediately jump from about 215 to 240+. These coolant temps occur regardless of the ambient air temp.

I'm concerned about how easily I can hit ECTs of 240+, even if I'm not pushing the Jeep very hard.

Between my GFC RTT and cargo, I've probably added 1000 lbs of payload which shouldn't be that big of a problem for the Jeep. I'm on 38's with 4.56 gears so my final drive ratio is slightly lower than stock, but again, that alone shouldn't affect the Jeep that much.

I've searched the forums and haven't seen much related to the cruise control issue. I'd welcome your feedback on that and the high coolant temps that I'm seeing.

I run CC often and never have an issue with the trans not shifting up or down and cruise at about 68-75 mph depending on the traffic. I too have 35s and 4:88 gears

 

[zouch]

excellent info; thanks for sharing (again)!

I've posted this before but it is probably good to push it out there once and a while.
It came directly from a MOPAR engineer when I was corresponding about heat issues with them a while back.
[snip]

 

[jriggsaz]

So based on what you all have said, many have seen the increased coolant temps that I've seen, but the issue of my transmission not downshifting and CC not being able to maintain speed appears to be rather unique to my Jeep.

It's also worth noting that my Banks iDash would show the "load" at nearly 100% while the Jeep was slowly dropping from 75 to 55 mph going up a hill. That makes me think that the Jeep had derated due to the coolant temps as pointed out in Plongson's post.

I have not played with manual fan control so I'll do some research on that to see if that might help the next time I'm pulling a hill with high ECT's.

I'm taking the Jeep to the dealer tomorrow so I'll let you all know if they come up with something.

 

[Plongson]

This just got posted and I got the link because several months ago I posted about looking for an aftermarket radiator...

Now I'm really interested! Wish there was a real world review with this radiator in a JLURD. This could be the answer to our high temp issue...

Aluminum Radiator

 

[jrice454]

I've posted this before but it is probably good to push it out there once and a while.
It came directly from a MOPAR engineer when I was corresponding about heat issues with them a while back.

I'm old school and still don't like this high temp. On top of that, when ambient is above 80°f, the coolant temp will climb FAST...

X2 on the thanks for sharing, great info!

 

[Terpsmandan]

Running 37’s on Mopar lift and everything else stock. When I am in the hills around my town I lock it into 7th and let the boost handle the load increase. If I leave it in 8th it will bog down and if it’s in D8 it will downshift all the way to 5th on the same hills.

 

[ChuckQue]

This just got posted and I got the link because several months ago I posted about looking for an aftermarket radiator...

Now I'm really interested! Wish there was a real world review with this radiator in a JLURD. This could be the answer to our high temp issue...

Aluminum Radiator

I’ve been tempted. I just worry about cracking it on a trail and being stuck. Aftermarket radiators are so hit and miss from what I’ve seen, but then again that’s probably just the internet echo chamber.

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