Towing gears and tranny temps (repeat issue I know I know...)

Rob Featherstone · October 3, 2018

I own a 2014, 5.3L 4x4 with the G80/GU6 3.42 gears Silverado W/T. I live in rockies in British Columbia and tow a 4500lbs (Dry) 6000lbs(truck and trailer gear loaded) wet travel trailer. If you guys watch The Discovery Channel you will have probably seen the show "Highway Through Hell" and that's the highway I tow on. Rule of thumb out here is that you double your towing capacity for what you're towing due to the steep grades if you want to keep your vehicle out of the shop. I probably tow along that highway about half a dozen times a year and I typically see transmission temps between 225F and 232F which is hotter than I'd like to see. I've installed the B$M deep aluminum transmission pan, and it seemed to drop it maybe 2-3F while towing, but still not enough to make me happy. My next endeavor is to maybe re-gear my truck. I use it to commute to work 50miles a day, and I get that I'll probably lose a bit of fuel economy on the highway, but its better than blowing a transmission with 2 young kids and an angry wife on the way to going on vacation!

I'm torn whether I should go with the 3.73 gears, or go balls deep to the 4.10 gears. I'm running stock size tires and no lift or leveling kit.

Secondly I'll probably end up going with the Diablo I3 to adjust performance with running higher octane fuel to get some minor gains while towing.

Any advice on which gear set I should consider is appreciated. Thanks!

pronstar · October 3, 2018

A deeper pan won’t appreciably lower temps. Just takes more time to heat or cool the larger volume.

You should consider a large tranny cooler, I prefer the ones with fans so they operate optimally regardless of airflow due to vehicle speed passing over them...you can mount them out of the way like under the vehicle.

IMHO 4.10 is too much gear for stock tires. And going from 3.42 to 3.73 isn’t really worth the expense. Especially since you didn’t mention a lack of power, which I wouldn’t anticipate with that light of a load.

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Centex14 · October 4, 2018

Larger cooler for sure.

I disagree on 4.10’s being to much. For towing that road (yes I’ve seen the tv show) your truck could use all of the mechanical advantage it can get. Transmissions heat up due to load and having the converter unlocked. 4.10’s can help ease the load and potentially keep the converter locked longer which helps keep temps down.

Rob Featherstone · October 4, 2018

Having thought about it, I'm more leaning towards a secondary cooler along with some performance mods. That way I can keep the benefits of better performance and retain the fuel mileage.

pronstar · October 4, 2018

Something like this would work great for you, methinks [emoji106]

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truckguy82 · October 5, 2018

On 10/3/2018 at 9:42 AM, Rob Featherstone said:

I own a 2014, 5.3L 4x4 with the G80/GU6 3.42 gears Silverado W/T. I live in rockies in British Columbia and tow a 4500lbs (Dry) 6000lbs(truck and trailer gear loaded) wet travel trailer. If you guys watch The Discovery Channel you will have probably seen the show "Highway Through Hell" and that's the highway I tow on. Rule of thumb out here is that you double your towing capacity for what you're towing due to the steep grades if you want to keep your vehicle out of the shop. I probably tow along that highway about half a dozen times a year and I typically see transmission temps between 225F and 232F which is hotter than I'd like to see. I've installed the B$M deep aluminum transmission pan, and it seemed to drop it maybe 2-3F while towing, but still not enough to make me happy. My next endeavor is to maybe re-gear my truck. I use it to commute to work 50miles a day, and I get that I'll probably lose a bit of fuel economy on the highway, but its better than blowing a transmission with 2 young kids and an angry wife on the way to going on vacation!

I'm torn whether I should go with the 3.73 gears, or go balls deep to the 4.10 gears. I'm running stock size tires and no lift or leveling kit.

Secondly I'll probably end up going with the Diablo I3 to adjust performance with running higher octane fuel to get some minor gains while towing.

Any advice on which gear set I should consider is appreciated. Thanks!

A member here did an extensive towing towing test and got great results by simply installing a lower temp engine thermostat and activating the fans at a lower temp.

I believe it was “Jon A” if you want to search

300 Blackout · October 8, 2018

The reason the trans, diff or engine will fail is overheated/degraded lubrication. You tow 12 times a year (6 trips there and back). If you don’t feel underpowered and your goal is to assure the reliability of the truck, then cooling the lubricants should be your primary focus. Re-gearing can help with this by increasing leverage thereby reducing strain on the engine and trans thus producing less heat. Obviously, only you know if the cost of re-gearing is justified for how you use the truck.

With 4.10s on your truck your engine RPMs at 70mph would be 2030 (Driveshaft RPM is 3032) and it would stay in V4 more often (I calculated based on 31.8” tire diameter). My truck has 4.56 gears and 33.5” diameter tires. At 70mph my engine is at 2175 RPM in V4 (my Driveshaft RPM is 3202) and it averages 19MPG on 87 gas at that speed. My guess is you would be around 20 to 21 mpg.

If you forego the gears and opt for engine, trans and even a differential oil cooler, you will certainly be decreasing the likelihood of a problem. Pronstar posted a nice Derale cooler. These self contained coolers are great. The fan faces down and there is a cover to protect the fins. The fan pulls air through the cooler and can be set up to activate at certain temps and turn off at certain temps with the right sensors. You certainly can do it for less money but it’s hard to beat the complete unit. Jegs sells their own house brand of hoses and fittings too which are reasonably priced (I just ordered them for my bypass oil filter setup).

If it was me, even with the new gears I would want the coolers just because the difficulty of the terrain. All it takes is one crash ahead of you or whatever to slow you down and suddenly your going at a turtle’s pace on rough terrain with no airflow to cool everything down.

No matter what you choose to do, I highly recommend you change out your trans fluid as soon as you can. If you are regularly seeing 220-230F on your trans fluid for extended trips then it’s probably in worse shape than you think. Same goes for your differential oil.

Adding a new differential cover to your rear end that allows you to change the oil without having to break the gasket is another good idea. I changed my diff oil last night after only 500 miles of driving with my new gears. The oil was filthy. I installed a PML cover and am very happy with it. It has a drain plug for easy oil changes and, if one day I choose to run a differential oil cooler, it can easily be plumbed in using the threaded drain and fill port. There’s also a spot to add a temperature sender if I choose.

Good luck. Please let us know what you end up doing and how it all works out.

Jon A · October 10, 2018

On 10/5/2018 at 7:15 AM, truckguy82 said:

A member here did an extensive towing towing test and got great results by simply installing a lower temp engine thermostat and activating the fans at a lower temp.

Yeah, I've been meaning to do a writeup on transmission temps and the data I've collected. Maybe in a week or two.

Long story short: In stock form, my transmission ran between 195-205 even on flat ground, not towing anything, even in cool weather. When towing, if any hills were involved it would go to the 230 degree range...I even hit 240 something once. After a few simple mods, my trans temps run 30-40 degrees cooler on average and has yet to hit 200 degrees, even when towing at 15,000+ GCW up long 6% grades in 90 degree temps. Basically for any given situation, you can expect the transmission fluid to be 30-40 degrees cooler than it would be with the stock setup. Your factory cooler is very large, the stock setup just doesn't use it very well.

Mods, in order of importance:

1) Bypass stock thermostat/install aftermarket thermostat. The stock thermostat is the main culprit. Truckguy82's was non-functional, but I don't like the design much--even when working correctly I don't believe it forces much fluid through the cooler until well over 200 degrees. This mod worked even better than I though it would. Transmission fluid heats up very slowly, so when you drop your baseline temp by 40 degrees or so, even on a very, very, long hill it just never has the time to get hot as it would stock as it takes a long, long time to make up that 40 degrees. Simply bypassing the stock one is pretty much free and will give you all the gains, but especially being in Canada adding an aftermarket thermostat is probably a good idea. I used a 140 degree just to set the floor--on long highway drives in sub-zero temps I'd be worried the trans temp may never even reach triple digits without one.

2) Program the fans to come on more aggressively. The fans help quite a bit even at highway speed, and obviously a ton at low speeds. You have a 2014 so it's probably out of warranty anyway, so that shouldn't be an issue. I show how to do it with HP Tuners in this thread:

You'll want to replace your engine thermostat with a cooler one to use those settings so the fans don't run all the time--the GM 194 degree or lower. I've found the 194 to work well, and you never have to worry about it leaking in the winter as you do with the aftermarket ones that have a different gasket design. If you had monitored your coolant and oil temps along with the trans temps, they likely would have scared you. The lower temp thermostat and fan settings help a ton for max coolant and oil temps.

3) By-pass the factory in-tank cooler in the radiator. It's almost always working as a heater instead of a cooler. I found doing this helped some at highway speeds, but quite a bit at low speeds. Again that's basically free and easy to do when setting up an aftermarket thermostat.

If you do those things, I guarantee you your trans temp issues will be a thing of the past.

You originally asked about gears. I would not recommend doing gears specifically for the purpose of reducing transmission temps. Yes, they will help by keeping you in higher gears longer, but I think older transmissions with fewer gears that didn't keep the converter locked nearly as much probably benefited more than these transmissions do. It's just a really expensive, round-about way to reduce transmission temps. Improving the transmission cooling system directly makes much more sense if that's your goal.

But gears are a great mod, especially with a 6-speed, especially for towing. They have lots of other benefits--will make the truck a lot more fun to drive, make towing more pleasant, improve grade-braking, etc. So I'm all for doing them for those reasons, just think of help with transmission temps as a side-benefit as that's a lot of money to spend if lowering trans temps is your only goal.