1BadAction

iTrader: (10)

You know this how? You don't, because the only thing you've towed with a gasser is a keyboard on the internet.

I've towed cross country with 8.1s and various other big block trucks of different EFI types multiple times, and if you're towing something heavy enough to make them hunt in and out of OD, they will get better mileage out of OD, Period. In drive (1:1) they are more likely (usually completely) stay out of PE and COT modes which both add fuel to the mix. If you had more than a 2nd grade understanding of EFI gasoline engines, this wouldn't even be an argument.



Will do man, I'm out.

Vindii

I own a Yukon XL 2500 8.1. Pretty much the exact same truck as the OP. Ive drive it daily and have thousands of miles towing a 10K lb 28 foot enclosed car trailer. So I think I have the experience to comment in this thread.

The OP is getting advice from a guy with a 5.7, a 6.0 and you with a old 454. Who's the keyboard jockey again?

If this motor trans combo got better MPG in 3rd VS 4th why wouldn't GM tell you not to tow in 4th at all? What would be the point in letting it shift at all if the mileage was better? Wouldn't GM know?

If you want to tell him it will be easier on the trans to tow in 3rd I'll agree 100%. But I know the MPG wont be better.

Take your 8.1 out and test it. Report back with the results...

Fast355

I already told you I have done testing!! Although the 8.1 was in an 18,000 lbs motorhome. OD in the Allison was practically WORTHLESS at 60-70 mph with the stock rear gearing. He ended up dropping the rear gear about 25% and had alot more torque to move the RV. If memory serves he went from 4.56 to 5.86:1.

Vindii

SO what was the details of your test. What was the MPG difference? How far did he test?

OP doesn't have an allison.

CaptCameltoe

iTrader: (3)

it's common sense and usually recommended not to tow in OD, why is that so difficult to comprehend?

Vindii

Old school thinking.

If you were correct GM would have locked out 4th when tow haul was activated.

CaptCameltoe

iTrader: (3)

people like you keep the trans shops in business, they thank you for your ignorance.

Vindii

So now where talking about tranny life? We were talking about MPG. Too different subjects.

Cant say Ive seen a bunch of 4L85-E trannys blown up from towing in 4th. But I'm sure you have.

Change the subject as you need to suit your posts.

CaptCameltoe

iTrader: (3)

you're my new hero, can tow 20k lbs at 90 mph and get 30 mpg in OD.

Vindii

Glad your coming around!

I get what you guys are saying. Its common to tow in lesser gears in older trucks. Newer trucks have better trans and bigger motors. I just dont see a point in locking it in 3rd with this motor trans. But if you want to go ahead. It wont hurt anything except suck up more fuel.

If its shifting all the time and the trans is getting hot lock it down a gear. If the trans temp is fine Id rather have the fuel mileage.