Have I been doing it wrong all these years?

[rollexx]

I have been towing our 30ft fiver for years with a Silverado 2500 Duramax. Have been using the tow mode and get right around 12MPG. Today we headed out. I zeroed out the trip computer before leaving. Stopped at a rest area about 100 miles out, all freeway traveling at about 60 as usual. It’s then I noticed I had forgot to put it in tow mode. Checked MPG reading and was surprised to see 15 MPG. Tran temp and engine temp were normal so just left it off the rest of trip, another 140 miles. Checked again at end and got 14.4 MPG. So my question.. On fairly flat highways should I leave towing mode off and only turn it on when I hit the hills?

[Bipeflier]

We use $100,000+ RVs weighing many thousands of pounds and we worry about fuel mileage? My guess is that most RVers don't drive over 10 to 20K miles per year. In the overall scheme of things 1 or 2 MPG isn't that big of a deal.

[hawkeye-08]

Yes, you will get better fuel economy without T/H on generally.

[mnaquaman]

Sorry - this ones going to be a bit long - there is son many things to consider.

There are two schools of thought on figuring fuel economy. One trust the computer or second compute it yourself based on the gas pump!

I had a co-worker that studied the pump method and its accuracy.
He found if you parked at the same pump in the same position every time your accuracy was right around 10%. know add in different pumps and vehicle positions?

When I hit the road I frequently check my MPG using both methods and rarely do they agree with each other! The computer normally tells me that my MPG is slightly higher (.3 mpg) than the pump method. So what do you believe?

I believe what one should be asking himself is this: Is my MPG consistent with my prior tank given the conditions? If they are then everything is good. Did my Mileage drop then why? Wind, Hills, Speed or other? If it's not the wind, hills or speed - is there something wrong with my vehicle?

Speed & wind are the biggest reason I see for a Mileage drop or gain!
driving 10 miles an hour faster is the same as driving into a 10 MPH head wind. For every 10 MPH increase in speed you can expect a 10% decrease in MPG.

I keep a log and at the end of the trip I'll figure out my MPG for the complete trip. If I hit my goal of 10 MPG I am happy. Some days are better than other, but I can say that I almost always are within a few tenths.

Happy camping and save travels!

[TravelinDog]

The engineers made the T/H mode hold the lower gears longer for a reason. If you choose not to use it that is your prerogative since it's your truck and trans life you are shortening.

[gmckenzie]

rollexx wrote:
I have been towing our 30ft fiver for years with a Silverado 2500 Duramax. Have been using the tow mode and get right around 12MPG. Today we headed out. I zeroed out the trip computer before leaving. Stopped at a rest area about 100 miles out, all freeway traveling at about 60 as usual. It’s then I noticed I had forgot to put it in tow mode. Checked MPG reading and was surprised to see 15 MPG. Tran temp and engine temp were normal so just left it off the rest of trip, another 140 miles. Checked again at end and got 14.4 MPG. So my question.. On fairly flat highways should I leave towing mode off and only turn it on when I hit the hills?

Had an 01 Sierra with the Duramax. I found it held the lower gear on flat roads so I'd turn off the T/H until it shifted and then turn it back on. Once in 5th, it would stay there with T/H on. But I liked T/H for getting up to speed and hills.

I doubt it would be a 3 mpg difference though.

[drsteve]

Terryallan wrote:

fj12ryder wrote:
The main thing to remember is that the MPG reading is a lie. If you really want to know your MPG, keep track of mileage and amounts added to the tank, over several tankfuls you'll get your pretty accurate MPG.

Let me understand. You trust your computer to tell you the number of miles you traveled. You trust your computer to tell you how fast you are going. You trust your computer to tell you the amount of time you traveled. You trust your computer to tell the engine what your foot wants it to do. You trust your computer to mix the correct amount of fuel with air, to allow the engine to run correctly.
But you don't trust your computer to be able to use all that information to figure your MPG? Instead you trust a hand held computer, and a simi accurate computer on a random gas pump on a simi level concrete pad to figure your MPG. Oke Doke!

The MPG is a calculated number, unlike the clock, odometer reading, etc, so it is more likely to be inaccurate. That said, hand calculating is not really any different.

[kellem]

dodge guy wrote:
TH doesn't care about flat ground. What it does is hold each gear longer when accelerating. When it's off it short shifts and can make the engine work harder building rpm back up which actually uses more fuel. I'm guessing you had a tail wind?

This ^

[Etstorm]

Doesn’t tow/haul also help engage the engine brake Incase of a sudden stop for traffic on flat ground?

[N-Trouble]

Ozlander wrote:
My 06 YukonXL has always, every fill, taken more gallons to fill than the computer says it used. Maybe around a gallon with a 25 gallon fill. New tires, old tires, still took more
I always figured the MPG shown was an optimistic estimate.

It is and will always be. Yet some will still try to argue all those pumps must be off by about the same amount.

[Ozlander]

My 06 YukonXL has always, every fill, taken more gallons to fill than the computer says it used. Maybe around a gallon with a 25 gallon fill. New tires, old tires, still took more
I always figured the MPG shown was an optimistic estimate.

[bguy]

If you're only going to keep the truck a couple years without a lot of miles then what odds. OTOH if you are going to keep it long term you can save a few bucks on fuel but eventually spend a lot of bucks on transmission. IMO at the very least follow the severe duty service schedule for AT fluid and filthers.

[nickthehunter]

Terryallan wrote:

fj12ryder wrote:
The main thing to remember is that the MPG reading is a lie. If you really want to know your MPG, keep track of mileage and amounts added to the tank, over several tankfuls you'll get your pretty accurate MPG.

Let me understand. You trust your computer to tell you the number of miles you traveled. You trust your computer to tell you how fast you are going. You trust your computer to tell you the amount of time you traveled. You trust your computer to tell the engine what your foot wants it to do. You trust your computer to mix the correct amount of fuel with air, to allow the engine to run correctly.
But you don't trust your computer to be able to use all that information to figure your MPG? Instead you trust a hand held computer, and a simi accurate computer on a random gas pump on a simi level concrete pad to figure your MPG. Oke Doke!

But...But...But... I read it on the internet it must be true!!!

[Grit_dog]

You guys are looking fir excuses to argue about stuff now.....sheesh.

To the OP, that seems like more of an anomaly than a phenomenon.
Mostly because 15mpg pulling a 30' 5th wheel doesn't seem very realistic.

[Terryallan]

N-Trouble wrote:

Terryallan wrote:

fj12ryder wrote:
The main thing to remember is that the MPG reading is a lie. If you really want to know your MPG, keep track of mileage and amounts added to the tank, over several tankfuls you'll get your pretty accurate MPG.

Let me understand. You trust your computer to tell you the number of miles you traveled. You trust your computer to tell you how fast you are going. You trust your computer to tell you the amount of time you traveled. You trust your computer to tell the engine what your foot wants it to do. You trust your computer to mix the correct amount of fuel with air, to allow the engine to run correctly.
But you don't trust your computer to be able to use all that information to figure your MPG? Instead you trust a hand held computer, and a simi accurate computer on a random gas pump on a simi level concrete pad to figure your MPG. Oke Doke!

Ok so on the flip-side if we assume my truck MPG readout is accurate than your implying every tested and certified gas pump Ive filled at is off by the same amount???

My truck always reads 6-7% above hand calculated numbers. This is directly attributed to “fuel used” value the computer tries to calculate. It is always 6-7% less than what the pumps say. These trucks have no gauge/meter to physically messure how much fuel the truck has actually burnt. Its all “calculated” numbers based on MANY engine parameters. A best guess estimate...

Some trucks are near spot on while others can be greatly off. Whichever you have will likey be consistent over the life of the truck.

Now back to the OP we all know nobody truly gets 15MPG towing a 30ft 5er out WEST. So just another datapoint that shows his computer numbers are BS.

Just saying. You use the computer generated miles to do your calculations. And you use a random gas pump, that may or may not have a level pad for the vehicle to sit on and if the one you used for the first fill did not have a level pad, or if the pad the vehicle sits on leaned slightly the opposite way. You are not getting a accurate reading.

For me. The computer is close enough. It has all the information needed to calculate MPG to a acceptable level.