Safe Transmission Temps

[sennister]

Originally Posted by 01tundra

Every one I've installed I may have lost a few drops of fluid, just have some ties of some sort to keep the cut hoses elevated while you're hooking them up.

I haven't had to even add fluid to the transmissions, I just fill the cooler through the top port with a hose and bottle pump prior to hooking the final hose up.

Yeah I agree if I just add a third cooler. I would have to add fluid to compensate for the increase in capacity to fill the new Aux Cooler. Also I am kind of leaning toward ripping out the OEM cooler and just putting a bigger one in if I do anything. So I will lose that fluid on top of the filling the new cooler. The benefit is that I have a lot more options this way rather than ripping apart the truck to see where I could squeeze in a third cooler, ordering one and having to rip it apart to install later. Also being I am dealing with the somewhat restrictive gill on the Denali, I also could better position a higher quality cooler this way. Heck I could even add the bigger cooler with a dedicated fan if I wanted. There looks to be enough room. That might make up for the restrictions.

[DocBrown]

Originally Posted by sennister

Heck I could even add the bigger cooler with a dedicated fan if I wanted. There looks to be enough room. That might make up for the restrictions.

I'm not sure it would. You can only put so much water through a 2 inch pipe, even if it's forced. Same principle applies to air flow. Only so much can get through the front.

[Dustdevil]

I used to tow 10k lbs in 105 degree temps up and down hills when we had a Duramax Crew Cab pickup and a toy hauler. On level ground, it would operate in the 185-190 degree range pretty consistently regardless of outside temp or load. But once we started climbing hills, the trans fluid temp would start rising to the 200, and occasionally as high as 215 range on hot days, especially if I just let the trans choose its own gears. What I began doing, once I became familiar with what gear would likely be necessary is to lock the trans in that gear as soon as the truck began to slow while starting up the steep hills. The trans heats up very quickly if you allow it to keep shifting back and forth trying to stay a gear too high. If you simply lock it in that lower gear and don't get in a hurry, at least it keeps the torque converter locked up and doesn't generate unnecessary heat.

But an extra cooler mounted in the right place doesn't hurt, either. Overheating that trans will shorten its life.

[sennister]

Originally Posted by DocBrown

I'm not sure it would. You can only put so much water through a 2 inch pipe, even if it's forced. Same principle applies to air flow. Only so much can get through the front.

Yeah, more for slow speed stuff. Give me a bit more cooling while stuck in traffic heading out of town during construction season which is in full effect. Every bit of cooling I can gain in situations like that will help later on in the hills.

[sennister]

Originally Posted by Dustdevil

I used to tow 10k lbs in 105 degree temps up and down hills when we had a Duramax Crew Cab pickup and a toy hauler. On level ground, it would operate in the 185-190 degree range pretty consistently regardless of outside temp or load. But once we started climbing hills, the trans fluid temp would start rising to the 200, and occasionally as high as 215 range on hot days, especially if I just let the trans choose its own gears. What I began doing, once I became familiar with what gear would likely be necessary is to lock the trans in that gear as soon as the truck began to slow while starting up the steep hills. The trans heats up very quickly if you allow it to keep shifting back and forth trying to stay a gear too high. If you simply lock it in that lower gear and don't get in a hurry, at least it keeps the torque converter locked up and doesn't generate unnecessary heat.

But an extra cooler mounted in the right place doesn't hurt, either. Overheating that trans will shorten its life.

Of course we are talking about different engines and transmissions but the 2011 (not sure which year it was added) but it has the +/- buttons on the shifter so I can take it out of D and into M and control gear selection that way. I actually did this going down a grade to do some more engine braking. No exhaust brake on it though like my Father in law has on his 1 ton Duramax.

[Wireman]

Originally Posted by Hazman65

Interesting question. I tow with a Jeep Grand Cherokee Diesel and keep a careful watch on all the temps, oil, coolant, and transmission. The Jeep makes it very easy as all can be displayed. I have never seen the numbers on my oil or my trans go much over what they are normally when I am not towing. My coolant is another story. It has never gone into the "red" but has gotten close on some long uphill grades. Trans temp stays in the 190s which the display shows in the normal range. The system on the Jeep is sealed! Can't check it the transmission fluid or ever change it! Doesn't sit well with me but I guess they expect the synthetic fluid to last the life of the vehicle and don't want a pathway for any contamination.

I have basically the same setup. 2015 JGC Limited Eco Diesel 4X4 W/tow pkg. It's a ZF 8 speed tranny with paddle shifters that I always use when towing so I can control what gear I feel comfortable with.

Towing capacity is 7200#. I tow a 23RLSW that I weighed and it was 5700# on the trailer axles setup to tow.

I did a 5200 mile road trip last summer thru Idaho, Wyoming, Montana, Colorado, and Utah. Obviously a lot of mountain driving. I bought a Scan Gauge II with X commands set up for the Eco Diesel. Wanted to monitor exact water temps and turbo exhaust gas temps.

I've included a PDF with readings I saved climbing the Baker grade from SoCal heading toward Vegas. It's a long steady climb of about 19 miles.


As you mentioned, on the dash water temp gauge, needle got very close to the red mark. Water temp at the top of the grade was 240 degrees per the Scan Gauge. Tranny fluid temp was 214 degrees.

With the nature of theses new trannys and the synthetic fluid available, higher temps are really not an issue. That said my opinion is there is no such thing as lifetime fluid life, especially when towing.

Since I tow a lot, I plan on changing the fluid & filter at about 35K miles. Hazman, here is some info on what needed and how it's done.

It is changeable and I included a video on a Ram 1500 which has the same tranny. Very expensive to do, but so is a new tranny. Found the fluid for $23/qt. and the pan & filter are a 1 piece design.

If I remember right about $190 for that. Has to be the ZF 8 speed fluid. I guess the Germans are getting pay back.

Like anything else, it's about doing the correct maint. and I tend to error on the side of caution with changing oil and other fluids before the recommended intervals. JMO

https://www.youtube.com/watch?v=mNo9Ln5KrOE

JEEP TOWING TEMPS ON BAKER GRADE 8-2016.pdf

[Hazman65]

Wireman, thanks for the information! I bought the Jeep used last year and I am closely tracking how much I tow with it. We pulled some decent grades through the Virginias going into North Carolina a few weeks ago. $190 isn't too bad for some piece of mind.

[WhiteHawker]

Originally Posted by sennister

Since we are talking the same generation truck. Did you have the KNP RPO Code so you had an Aux that you removed or was it just adding the new one? Transmission is the same in both applications, I just have the 6.2 vs the 5.3 engine.

EDIT: I just looked at the amazon link. Interesting that it has a thermal bypass. Did you install that on yours? It claims to act like a thermostat where it won't flow through the cooler until temps hit 180F. That would mean that if you are running 145-160 in normal driving it actually isn't doing anything unless you left that off. I would consider leaving it off as it reduces a point of failure. However in the middle of winter when it is -20f out it might be nice to have it automatically shut down.

Unfortunately, my truck did not have a factory aux tranny cooler, my install was new...

I'm not convinced the bypass is worth the effort of install. I did put the thermal bypass in, but the temp setting of 180 doesn't do much for it as the tranny never sees anything over 180 unless pulling the TT. Year round I see 145-160 maybe 170 if I'm really thumping on it on a hot day without TT I also installed a BlackBear turner allowing me to adjust line pressure etc. to improve shifting. It gave the 5.3 a nice shot in the arm as well.