2500HD gas mileage

Truston Gunter · August 1, 2022

I tried towing with out using the tow haul mode on our recent camping trip from south texas to florida. at our halfway mark this popped up????

I read somewhere that the tow haul mode improved engine cooling. Even though my bumper pull camper is only 7500 lbs, I get similar mpgs like FALTUS does. Here is a gas tracker for anyone that may be interested in my experience.

Flatus · August 1, 2022

6 hours ago, Truston Gunter said:

I tried towing with out using the tow haul mode on our recent camping trip from south texas to florida. at our halfway mark this popped up????

I read somewhere that the tow haul mode improved engine cooling. Even though my bumper pull camper is only 7500 lbs, I get similar mpgs like FALTUS does. Here is a gas tracker for anyone that may be interested in my experience.

Man, I would hate to see that message. I have not ever noticed my engine temp getting high although I don't pay as close as attention to it as my transmission temp. My trans temp usually stays below 185 while towing.

Another JR · August 2, 2022

It’s interesting the coolant temp gage shows normal thermostat temperature. I wonder what temperature the computer is sensing for that message. An exhaust gas temperature somewhere with a cooling cycle requirement to clear the message? Oil temperature?

Truston Gunter · August 3, 2022

I read somewhere ( might have been this forum) that after a long and\or heavy tow, this message appears so you don't immediately turn off the vehicle and give it time to cool. I assume having the tow/haul engaged has some additional cooling parameters that are active. I have not had this message reappear but I also have the tow/haul mode engaged when I'm pulling my camper.

mtbadbob · August 4, 2022

I haven't towed with mine yet, but did tow my job trailer a little with my AT4 gasser. I noticed with both 6.6 gassers that they do better than my '15 w/6.0 & 4:10 gears. It's way easier to hit the 14-15 mpg range on these new gassers than my '15. I've tried different tires, cat-backs, CAI's, programmers, etc. to obtain the best mileage, so I can tell you that with every inch of tire increase, comes almost an mpg decrease. Bottom line is these new 6.6's are definitely better for power & mileage than the 6's, and I've done over 300k with my last two 6.0's. I can see possibly 16-17 mpg on long, steady roads trips, although mountain mpg's are a bit different than flat land mpg's!

MacLaren · August 9, 2022

Never had that message but, tow haul mode isn't even recommended until your hauling over 12,000 pounds if I'm not mistaken. Ya don't wanna burn up your tranny. Plus, these trucks have a radiator the size of Montana. - I've towed quite a bit and nary a hiccup, knock on wood.

My mpg not towing has always been between 16-18mpg (this of course doesn't count the first 1500 miles

mtbadbob · August 10, 2022

On 8/9/2022 at 4:16 AM, MacLaren said:

Never had that message but, tow haul mode isn't even recommended until your hauling over 12,000 pounds if I'm not mistaken. Ya don't wanna burn up your tranny. Plus, these trucks have a radiator the size of Montana. - I've towed quite a bit and nary a hiccup, knock on wood.

My mpg not towing has always been between 16-18mpg (this of course doesn't count the first 1500 miles

I've done over 310k on 4 different 6L's and I run with tow/haul mode a lot. I've never had any issues with these tranny's. I like how they shift better in the tow/haul mode, and they save on your brakes.

Flatus · September 5, 2022

I did another tow this weekend. I pulled the travel trailer from Biloxi to Starkville which is about 260 miles. I got 8.6 on the way up and 8.3 on the way back down. I tried towing without tow/haul for just a short bit and it seemed to shift between 5th and 6th too often. I put it back in tow/haul and stays in 5th the majority of the time with occasional downshifts to 4th (up hill) which while it is in 4th it will hit about 2800 RPM. I had stated earlier in the thread that it will go over 3000 rpm but I was incorrect on that that. I guess this is just going to be the norm. This is a hilly drive though, constant up and down.

sheath · September 6, 2022

18 hours ago, Flatus said:

I did another tow this weekend. I pulled the travel trailer from Biloxi to Starkville which is about 260 miles. I got 8.6 on the way up and 8.3 on the way back down. I tried towing without tow/haul for just a short bit and it seemed to shift between 5th and 6th too often. I put it back in tow/haul and stays in 5th the majority of the time with occasional downshifts to 4th (up hill) which while it is in 4th it will hit about 2800 RPM. I had stated earlier in the thread that it will go over 3000 rpm but I was incorrect on that that. I guess this is just going to be the norm. This is a hilly drive though, constant up and down.

Hope you had a good trip (besides fuel mileage). That is a pretty drive.

Still seems a bit on the low side to me. But what do I know...

Next time you make this trip it might be worth setting the cruise control (if possible) and leave tow/haul off. Let it shift as it likes, just watch the transmission temp. I would have thought you'd be a mid 9mpg with your setup, and GCW.

The only thing that I don't like about that is the cruise lets speed drop 3-5mph before correcting with a down shift. I'll normally depress the gas pedal to get a downshift as soon as it starts to drop speed. That process helps keep the speed more consistent.

Hth,

Flatus · September 6, 2022

5 hours ago, sheath said:

Hope you had a good trip (besides fuel mileage). That is a pretty drive.

Still seems a bit on the low side to me. But what do I know...

Next time you make this trip it might be worth setting the cruise control (if possible) and leave tow/haul off. Let it shift as it likes, just watch the transmission temp. I would have thought you'd be a mid 9mpg with your setup, and GCW.

The only thing that I don't like about that is the cruise lets speed drop 3-5mph before correcting with a down shift. I'll normally depress the gas pedal to get a downshift as soon as it starts to drop speed. That process helps keep the speed more consistent.

Hth,

I do use cruise when traveling but with tow/haul. I set it at 65 mph and you are correct, it will drop to 61 mph before downshifting to get back to 65mph. My transmission temp never goes above 180 while using tow/haul. I kinda think it will get above 180 if not using tow/haul because of the frequent shifting between 5 and 6 but I have not tried for a significant distance.

Ray Pickle · September 8, 2022

I drive a little slower most of the time, around 62 mph. I do not use cruise control in anything but predominatly flat terrain for that exact reason. I pickup speed on downhills, maybe up to about 67- 70 mph, whatever existing steady pedal pressure achieves within reason, anticipating bleeding speed on uphills. Much more efficient than losing 3 or 4 mph while climbing before downshift and then attempting to regain lost speed while climbing.

Flatus · September 8, 2022

5 hours ago, Ray Pickle said:

I drive a little slower most of the time, around 62 mph. I do not use cruise control in anything but predominatly flat terrain for that exact reason. I pickup speed on downhills, maybe up to about 67- 70 mph, whatever existing steady pedal pressure achieves within reason, anticipating bleeding speed on uphills. Much more efficient than losing 3 or 4 mph while climbing before downshift and then attempting to regain lost speed while climbing.

I think I'm just too damn lazy to not use cruise.

Stand By · September 15, 2022

Empty and with light traffic, these get pretty decent mileage on two lane highways under 65 mph. Not bad on the freeway doing the speed limit. Higher speeds, passing and hills, it'll drink it, but it gets it don't better than a 5.3 at freeway speeds. I also don't get quite as much "jet lag" as I did in the 5.3 on long trips. I/e not as fatigued.