2013 Tahoe/Towing question

[Geotrash]

Assuming OP's Tahoe has the factory trans cooler, a larger one is unnecessary IMHO. 190-200° F is normal operating range for the 6L transmissions. Dex6 has substantially better high-temperature capabilities than Dex3. And low temps can be just as bad, or even worse, than high temps. If you're not getting above ~150°, you're not boiling off condensation that may have collected in the transmission. And we all (should) know that water in the fluid is bad.

I just have the small factory cooler in my Suburban. 240k miles, still original, still operates perfectly. And I beat the crap out if it. If I'm just driving, I'm cruising down the highway and high speeds (90-100+), or I'm towing either my 4,000-lb cargo trailer or 8600-lb travel trailer.

My personal record is 243°, usually achieved when I'm going over the Continental Divide with the travel trailer. I simply change the trans fluid more frequently. Sometimes with an interval as low as 30k miles. But usually I do it every 50k. Full flush - at the dealership. 16 quarts.

This was on I-70 eastbound towards the Eisenhower Tunnel, 7% grades, pulling the behemoth right at 16,000 lbs gross vehicle weight...

Tiny cooler:
View attachment 397348

^^^This.^^^

I have researched this one to death for my own towing rig (2012 Yukon XL Denali). I have a trucool 40K on my '07 and I wish I hadn't done it. I installed it before I read GM's guidance on transmission temperatures. GM likes to see a minimum temperature of 150ºF in operation. Below that there can be problems with moisture accumulating in the fluid for various reasons. With the trucool I can't get my transmission temps above 125-130ºF for a third of the year (winter) and the rest of the year it rarely makes it to 150ºF in normal driving. Towing our 7500 lb camper I might see 175ºF for short times. These numbers are about 50ºF lower than with the factory cooler, which is too much cooling.

The second problem with the trucool is that it blocks too much of the radiator leading to engine cooling problems. My engine coolant in the '07 runs about 15-20ºF hotter when towing and has even gotten hot enough to trigger a warning message in the DIC for the engine coolant temp.

On my 2012, I took a different approach. I installed a Derale 13960 plate cooler with a thermostatically controlled fan behind my lower grille so it wouldn't obstruct the radiator. Now I see normal transmission operating temps of 175ºF year round and 190ºF when towing on level ground. In heavy traffic or climbing mountain passes I might see a peak of 225ºF but that fan cools it off really quickly back to normal. All of this is well within the normal operating parameters of the 6L80.

Long story short, if the OP's truck has the factory external cooler, I wouldn't change a thing. If it doesn't, I'd install either the factory cooler or the Derale. GM had this one engineered right in the OEM design, in my opinion.

 

[donjetman]

^^^This.^^^

I have researched this one to death for my own towing rig (2012 Yukon XL Denali). I have a trucool 40K on my '07 and I wish I hadn't done it. I installed it before I read GM's guidance on transmission temperatures. GM likes to see a minimum temperature of 150ºF in operation. Below that there can be problems with moisture accumulating in the fluid for various reasons. With the trucool I can't get my transmission temps above 125-130ºF for a third of the year (winter) and the rest of the year it rarely makes it to 150ºF in normal driving. Towing our 7500 lb camper I might see 175ºF for short times. These numbers are about 50ºF lower than with the factory cooler, which is too much cooling.

The second problem with the trucool is that it blocks too much of the radiator leading to engine cooling problems. My engine coolant in the '07 runs about 15-20ºF hotter when towing and has even gotten hot enough to trigger a warning message in the DIC for the engine coolant temp.

On my 2012, I took a different approach. I installed a Derale 13960 plate cooler with a thermostatically controlled fan behind my lower grille so it wouldn't obstruct the radiator. Now I see normal transmission operating temps of 175ºF year round and 190ºF when towing on level ground. In heavy traffic or climbing mountain passes I might see a peak of 225ºF but that fan cools it off really quickly back to normal. All of this is well within the normal operating parameters of the 6L80.

Long story short, if the OP's truck has the factory external cooler, I wouldn't change a thing. If it doesn't, I'd install either the factory cooler or the Derale. GM had this one engineered right in the OEM design, in my opinion.

Did you install the optional thermostatic bypass?
They make several smaller cooler too.

 

[Geotrash]

Did you install the optional thermostatic bypass?
They make several smaller cooler too.

I didn’t. It didn’t ship with one and when I installed it I hadn’t had enough experience with it to know that it would be an issue. It wouldn’t help with the radiator blocking issue though.

 

[B-train]

Assuming OP's Tahoe has the factory trans cooler, a larger one is unnecessary IMHO. 190-200° F is normal operating range for the 6L transmissions. Dex6 has substantially better high-temperature capabilities than Dex3. And low temps can be just as bad, or even worse, than high temps. If you're not getting above ~150°, you're not boiling off condensation that may have collected in the transmission. And we all (should) know that water in the fluid is bad.

I just have the small factory cooler in my Suburban. 240k miles, still original, still operates perfectly. And I beat the crap out if it. If I'm just driving, I'm cruising down the highway and high speeds (90-100+), or I'm towing either my 4,000-lb cargo trailer or 8600-lb travel trailer.

My personal record is 243°, usually achieved when I'm going over the Continental Divide with the travel trailer. I simply change the trans fluid more frequently. Sometimes with an interval as low as 30k miles. But usually I do it every 50k. Full flush - at the dealership. 16 quarts.

This was on I-70 eastbound towards the Eisenhower Tunnel, 7% grades, pulling the behemoth right at 16,000 lbs gross vehicle weight...

Tiny cooler:
View attachment 397348

Yours is a 3/4 ton. Different trans designed for above said use. Ive had the same power train in a work truck and it is much more robust than the 1/2 tin version. The lighter duty guy wouldn't hold up to that for those miles in my mind.

But, I have see a few transmissions go way farther that I ever imagined by having frequent servies.

 

[j91z28d1]

for you guys that are over cooling tranny fluid. are these add on coolers still using the in radiator cooler? if so, just swap the lines so that it goes the the aux cooler first and then into the radiator. that will stabilize the Temps to your coolent Temps. if fluid is cooler going in, it will warm it up and help with the air blockage on the coolent side. if you're working it hard and the aux cooler can't completely bring the Temps down. the radiator will do it.

also if there's room, you can move the cooler behind the radiator. its the same idea, but relying on the warm air from the radiator to equalize stuff.

 

[intheburbs]

Yours is a 3/4 ton. Different trans designed for above said use. Ive had the same power train in a work truck and it is much more robust than the 1/2 tin version. The lighter duty guy wouldn't hold up to that for those miles in my mind.

But, I have see a few transmissions go way farther that I ever imagined by having frequent servies.

Yes, I'm aware of the 6L80/6L90 differences. I do own 1 of each. They both use Dex6, and both benefit from frequent/regular service intervals. Plus, OP is only talking about flat-towing a Wrangler, not towing a gigantic trailer. So the only added work the Tahoe trans has to do is overcome the rolling resistance of the tires and axles of the Jeep.

He'll be fine, and doesn't need to add an extra cooler (assuming he does have the factory trans cooler).

 

[B-train]

Yes, I'm aware of the 6L80/6L90 differences. I do own 1 of each. They both use Dex6, and both benefit from frequent/regular service intervals. Plus, OP is only talking about flat-towing a Wrangler, not towing a gigantic trailer. So the only added work the Tahoe trans has to do is overcome the rolling resistance of the tires and axles of the Jeep.

He'll be fine, and doesn't need to add an extra cooler (assuming he does have the factory trans cooler).

Gotcha. I was thrown off by the pic of the 3/4 ton in your driveway. Agree 100% that he'll be fine flat towing with his 1/2 ton.

Was the 243F in your 1/2 ton or 3/4 ton? The highest I've experienced climbing mountain trails in CO was about 217F and I wasn't too keen on that, but it's good to have your experience input.

 

[Geotrash]

for you guys that are over cooling tranny fluid. are these add on coolers still using the in radiator cooler? if so, just swap the lines so that it goes the the aux cooler first and then into the radiator. that will stabilize the Temps to your coolent Temps. if fluid is cooler going in, it will warm it up and help with the air blockage on the coolent side. if you're working it hard and the aux cooler can't completely bring the Temps down. the radiator will do it.

also if there's room, you can move the cooler behind the radiator. its the same idea, but relying on the warm air from the radiator to equalize stuff.

I ran the experiments of different routing of the plumbing for the cooler, including taking the radiator's oil-to-water cooler out of the system entirely back in 2021 and it didn't work. Couldn’t keep temps under control. It’s all documented here: https://www.tahoeyukonforum.com/thr...ontrol-when-towing-in-the-summer-heat.125753/

The GM upfitters manual is also clear that any aux cooler should be plumbed inline after the radiator and before the transmission in the fluid path.

I considered moving the trans cooler to behind the radiator but that creates several complications for the fans and other clearances. In the end I decided that since I have a lower grille on the Denali, I would locate the Derale there and punch out the plastic plugs to get airflow to it. I've found it to be about the perfect setup for towing near the max rated capacity of the truck.

On the 1/2 vs 3/4 ton topic, the 6L90 uses the same torque converter as the 6L80 and I believe the factory external transmission cooler is the same as is used on the 1/2 ton with the 6L80, so I would expect their capacity to generate and manage heat to be nearly identical.

 

[intheburbs]

Gotcha. I was thrown off by the pic of the 3/4 ton in your driveway. Agree 100% that he'll be fine flat towing with his 1/2 ton.

Was the 243F in your 1/2 ton or 3/4 ton? The highest I've experienced climbing mountain trails in CO was about 217F and I wasn't too keen on that, but it's good to have your experience input.

I was simply showing the size of the factory cooler with the pic of my 3/4-ton.

The highest trans temps I've seen were all pulling the behemoth trailer over Continental Divide passes with my 2500. Gross combined weight right around 16,000 lbs. Primarily Powder River Pass and the Eisenhower Tunnel.

The "trans hot idle engine" warning only triggers at 265°. The "heat bad" crowd still has a strong presence here. I don't know if it's Dex3 guys upgrading their rigs and not understanding Dex6's capabilities, or whatever.

Again, I have a data set with 1 sample - but my Suburban has 240k miles and it's still the original 6L90. Probably 20k miles towing the 8600-lb behemoth, and another 20k pulling my enclosed 6x12, which is about 4,000 lbs.

 

[Geotrash]

The highest I've experienced climbing mountain trails in CO was about 217F and I wasn't too keen on that, but it's good to have your experience input.

For what it's worth, I lived in Colorado for 25 years and pulled trailers all over, and also pulled our current camper over some of the passes out there in 2021. I was shocked to learn that here in the east I have seen just as high of engine and transmission temps over the Blue Ridge in Virginia (on 33 between Standardsville ind Elkton) and also down just east of Asheville, NC on 40 as I saw out west.

On 33 with the factory cooler I saw 237ºF for the transmission one summer day, which is what prompted me to start researching and experimenting. Then I learned what GM has to say about transmission temps in the 6L80 and realized that I needn't have worried and that the factory coolers are plenty adequate. I still had another 30º to go!

As @intheburbs says, there are still lots of folks around clinging to ancient wisdom dating back to the 700R4 days with Dino fluids and old seal materials who have an unshakable belief that you can't overcool transmission fluid. It doesn't help that there are charts everywhere on the interwebz that show impending transmission death above 200ºF for more than 100 miles. But it turns out that you can indeed overcool the fluid, from an engineering perspective and that current transmissions and fluids are designed to handle more heat.