How to determine Towing power?

[intheburbs]

That's why literally everything we take camping with us goes into the trailer and not into the back of the Yukon. The ONLY things in the Yukon, besides seats and a steering wheel, are 2 adults, 2 small-ish kids (10 and 13), and a 65 lb. dog (all in about 650 lbs. of meat ). We even take the third row out on most camping trips. But again, that 6.2L pulls it all with ease and the truck and camper combo are very stable.

It's not the engine you should be worried about. Based on just the engine, hell, you could pull 15,000 lbs.

First, you have a less-than-optimal axle ratio - 3.42. 3.73, 4.10 or aftermarket 4.56 are better for towing. Second, I've always felt the weak link of the GM half-tons is the rear axle. Semifloater, prone to overheating on long drives with heavy loads. My 2001 Suburban is wearing rear axle number 4 precisely because of heavy long-distance towing. Third - weak half-ton brakes. The half-tons are underbraked. But I would expect with the 20s, you'd have the clearance to upgrade the size of your rotors.

Lastly, for those with newer GMT900s - don't get complacent and think the truck and integrated trailer brake will get you out of a death-sway. Make sure you've trained yourself to manually apply the trailer brakes in case of sudden/excessive sway. You have to pull out of excessive sway - you need tension on the hitch. You accomplish that by either mashing the gas (EXTREMELY counter-intuitive) or manually applying the trailer brakes. Practice it to a point you can do it instantly, without looking.

 

[Geotrash]

It's not the engine you should be worried about. Based on just the engine, hell, you could pull 15,000 lbs.

First, you have a less-than-optimal axle ratio - 3.42. 3.73, 4.10 or aftermarket 4.56 are better for towing. Second, I've always felt the weak link of the GM half-tons is the rear axle. Semifloater, prone to overheating on long drives with heavy loads. My 2001 Suburban is wearing rear axle number 4 precisely because of heavy long-distance towing. Third - weak half-ton brakes. The half-tons are underbraked. But I would expect with the 20s, you'd have the clearance to upgrade the size of your rotors.

Lastly, for those with newer GMT900s - don't get complacent and think the truck and integrated trailer brake will get you out of a death-sway. Make sure you've trained yourself to manually apply the trailer brakes in case of sudden/excessive sway. You have to pull out of excessive sway - you need tension on the hitch. You accomplish that by either mashing the gas (EXTREMELY counter-intuitive) or manually applying the trailer brakes. Practice it to a point you can do it instantly, without looking.

Thankfully I have had better luck with rear axles. Both my 2007 and 2012 XL Denalis are still wearing their originals, with 130K and 220K, respectively. I attribute their longevity to the fact that the AWD system is sharing the work with the front axle, full time, and that I change the fluid every 20K or so. I agree that 3.42 is suboptimal, but is helped by having a 6-speed at least.

I find the brakes on both of my Denalis adequate for my towing purposes. I'm running ceramic pads and Powerstop rotors on the 2007 and still have the original pads and rotors on the 2012 with lots of life left. I also use engine braking to keep from heating up the brakes too much in the mountains. Back in the 90s I hauled an industrial centrifuge (weighed about 8000 lbs with a gooseneck trailer) all over the western US behind a brand new '95 Chevy 3500 dually with the 454. These Denali's will out pull and out stop that pig any day of the week and twice on Sundays, so it's all relative. The GMT900 is a solid towing platform if you keep it within its limits.

All of that said, I've been looking at upgrading to the 14-bolt rear axle from a 2WD Escalade. They're widely available and inexpensive, but will likely only pull the trigger if I have any trouble with mine. I'll also likely upgrade the brakes on the 2012 once the originals wear out. It's an easy upgrade and yes, larger rotors will fit behind the 20s nicely.

 

[swathdiver]

First, you have a less-than-optimal axle ratio - 3.42. 3.73, 4.10 or aftermarket 4.56 are better for towing.

How do you like the 3.73s for towing Bill? They pull down the rpms about 5 mph compared with the 3.42s so 4th gear at 70 mph is 3000 rpms, which is 3000 @ 65 mph with 3.73s in 4th.

 

[intheburbs]

How do you like the 3.73s for towing Bill? They pull down the rpms about 5 mph compared with the 3.42s so 4th gear at 70 mph is 3000 rpms, which is 3000 @ 65 mph with 3.73s in 4th.

The 6.0 loves to rev. I'm usually in 4th when towing heavy on the highway. I let her eat! I always tow heavy in "M," because I don't want it gear-hunting. On steeper grades I'll wind it higher, letting the VVT kick in for a little extra power boost.

What drove home the importantness(?) of axle ratios is the comparison between my two trucks.
Sierra Denali - 5500 lb curb weight, 3.42, 400 HP
Suburban 2500 - 6500 lb curb weight, 3.73, 350 HP, Blackbear tune

I've never actually raced them head to head.
Denali - 1000 less pounds, 50 more HP, AWD
Suburban - better axle ratio, Blackbear tune

No contest, right? But from my obviously extensive wheel time behind each, I actually think it's pretty close. Here's my expectation of the result of a drag race from a light...

Denali jumps out to an early 1- or 2-car length lead. But after about 30 MPH, the Suburban slowly starts to close. The higher ratio keeps the engine higher in the power band. Probably around 70-80, the Suburban pulls even, then at 100 the Denali hits the governor and the Suburban walks away on its way to 120+. Seat of the pants 0-60 times? I'd say 6 flat for the Denali and 6.2-6.3 for the Suburban.

Yes, the tune firmed up shifts and increased throttle response, but the 10% difference in gear ratios is the difference, IMHO. Simple gear change offsets 50 hp and 1000 lbs.

Having the two GMT900 trucks allows me to make some good comparisons. Another eye opener was the effect of tow vehicle wheelbase on towing smoothness and stability. I also have a 6x12 enclosed single-axle cargo trailer I tow frequently. Usually I tow it with the Suburban. It's about 4,000 lbs, and has no trailer brakes. The Suburban has a 9900-lb braking system (RPO JH6), so it's better suited for towing the trailer. The ride is pretty choppy, especially on the ****** Michigan highways like I-94. But then one time I towed the trailer with the Denali. Even though it is 1000 lbs lighter, the extra 14 inches of wheelbase made for a remarkably smooth tow. I was shocked at the stark contrast. Again, the Denali brakes aren't really up to the task, but frankly I'd rather tow that trailer with the half-ton, rather than the 3/4-ton.

 

[Mickey_7106]

Everyone makes great valid points. I have little experience towing but did drive a 14k lbs Rv, so take my recommendations with a grain of salt. I had very little wiggle room when loading up the rv to camp.

You'll probably want some E Load rated tires at minimum. Upgrade your brake pads to HD/towing rated. Tow air bags for the rear or a hitch weight distribution. Think I read that increases your town capacity to 12k lbs? Also everyone is talking about coolers but since it snows where you live you might want to consider one of those remote oil thermostat units.

 

[Geotrash]

Also everyone is talking about coolers but since it snows where you live you might want to consider one of those remote oil thermostat units.

^^^YES.

That's precisely why I went with the Derale 13960 cooler. It has a thermostatically controlled fan so that the fluid heats up to operating temperature faster, but the fan cools it down before it gets too hot. It's the best solution I've found for these trucks when towing heavy in the summer heat. It outperforms the factory cooler under load but doesn't have the downsides that the Trucool 40k does, which doesn't allow the fluid to heat up enough in the winter (GM says 150ºF is the minimum recommended operating temperature for the 6L80E), and blocks too much airflow through the radiator, creating an engine cooling problem when towing heavy in the summer. I mounted the Derale below and behind the front bumper, so it's out of the path of airflow through the radiator and it works great.

 

[Just Fishing]

^^^YES.

That's precisely why I went with the Derale 13960 cooler. It has a thermostatically controlled fan so that the fluid heats up to operating temperature faster, but the fan cools it down before it gets too hot. It's the best solution I've found for these trucks when towing heavy in the summer heat. It outperforms the factory cooler under load but doesn't have the downsides that the Trucool 40k does, which doesn't allow the fluid to heat up enough in the winter (GM says 150ºF is the minimum recommended operating temperature for the 6L80E), and blocks too much airflow through the radiator, creating an engine cooling problem when towing heavy in the summer. I mounted the Derale below and behind the front bumper, so it's out of the path of airflow through the radiator and it works great.

I was thinking about that pretty seriously.
I added a bigger cooler that worked great in the summer, but in the winter the fluid was pretty close to body temperature after a good drive.

Luckly on my S10 the grill is really easy to pull.

So, during the winter I just tape off part of the cooler in order to get the fluid above 100f


On the HoeMare,
For my new cooler setup, I'm thinking about going with a Y for the feed and return.
One feed will go to the radiator cooler.

The other feed will go to the cooler in the front of the radiator.
On that line, add a little valve to control the flow.

That way I can both control the back pressure I'm reading, and the transmission fluid temperature.
(And the pressure reading comes off of the feed line going into the cooler line filter.)

Overthinking it, but I'm thinking what the hell!

For my transmission cooler, I have a double pass 1/2in unit that's a left over from my garage air system/compressor install.
It was going to act as an air cooler/water separator, but I went a different route instead.
I'm curious to see how it does as a transmission cooler.

This will also allow me to see the resistance difference between the radiator and the front cooler setup with the lines plumbed with -8AN.

 

[donjetman]

Both Derale and Tru-Cool sell thermostat bypass valves for cold wx climates.

 

[sonic2211]

Welcome to the forum Sonic. First, I suggest looking for 2012-2014 models because they have Trailer Sway Control, Hill Start Assist and Improvements with Powertrain Grade Braking and Cruise Grade Braking. Like Dave, JL1, the Integrated Trailer Brake Controller is a must have, won't consider a truck without one. No, it cannot be added! LOL

Ok, if you come across a 5.3 and it has 3.08 gears, pass on it. If you come across a 5.3 with 3.42 gears, you have to make sure that it has K5L in its RPO sheet so that you know it is rated for the maximum tow rating. Same goes for the 6.2 Denalis. Some of them do not have the external engine oil cooler and external transmission cooler either.



Sign up to Compnine, $5 for 5 RPO Sheets.



If you are looking for a real unicorn, in 2010 GMC made Yukon XL SLTs with the L9H 6.2, no AFM, and they can be found as 4x4s or RWD. Thus far we've only located just under 40 but they do show up for sale every month or so, usually all but used up mileage wise.


We can still see your VIN Dave! LOL

Your girl weighs 100 pounds more than mine! Is that what those Dubs and air suspension add? My payload capacity is 1499 pounds with the same GVW Rating, so her original curb weight was 5901. Right after I put the new Michelins on, the CAT Scales say she weighed 5860.

Question for Dave and Bill @intheburbs @Geotrash : How far on average is your daily run while towing a travel trailer?

View attachment 364113

I am wondering about whether what you mentioned as being important in the 2012-2014 models is really a deal breaker? I have found a 2011 Yukon XL Denali with <140,000 miles that has JL1, KC4, KNP, Z55, C6C, GU6, Z82, VR4. So trying to determine whether I really need the upgrades in the 2012-2014 models that you mentioned. That being said, I also found a 2012 Yukon XL Denali with a bit more mileage ~150,000 and a couple thousand more in price with the same line up of RPO codes. Is it worth it to buy the 2012 model??

 

[swathdiver]

I am wondering about whether what you mentioned as being important in the 2012-2014 models is really a deal breaker? I have found a 2011 Yukon XL Denali with <140,000 miles that has JL1, KC4, KNP, Z55, C6C, GU6, Z82, VR4. So trying to determine whether I really need the upgrades in the 2012-2014 models that you mentioned. That being said, I also found a 2012 Yukon XL Denali with a bit more mileage ~150,000 and a couple thousand more in price with the same line up of RPO codes. Is it worth it to buy the 2012 model??

You'll have to answer that one for yourself, can you live without TSC and HSA and the cruise control changes? How about the upgraded navigation unit? If you have a good sway control and weight distribution hitch then those things aren't as critical to have, just nice to haves and you'll have a little more jingle in your pocket!