I have a 2005 Fleetwood Southwind 37c with the 8100 Vortec V8 with an Allison 5 speed transmission with 28000 miles that gets very poor gas mileage, about 6 mpg towing my boat or pickup and 7 mpg empty. I tried the UltraPower chip which seemed to do almost nothing and then installed the complete Banks system (headers, muffler, exhaust, Ramair, and the Auto power tune. A little more power, but still the same fuel mileage. This is driving between 60-65 mph. The boat weights about 3700 lbs and the pickup about 5000 lbs. I read about guys getting 8 to 8.5 while towing and even better empty. The motorhome seems to have adequate power, but still will not run with the Ford 3v V10. There are no trouble codes on the engine or powertrain modules. I do notice that the inside of the exhaust pipe is jet black and rubs off on your finger. The Fords exhaust I looked at are clean and only a very little brown on your finger. I have not checked any other Chevy 8100's. The motor starts and runs perfectly and outside of the super noisy thermostatic fan and the poor fuel mileage the coach drives and runs very good. Any help would be appreciated. Thanks.....

Have you tried 91 octane fuel? While it might seem more expensive, I did find I got more than 10% better mileage, so the extra $0.20 per gallon gave me more miles per $100 in fuel! It might also be a knock sensor that is picking up pinging, and is setting back the timing, and increasing fuel usage to compensate for pinging that is not really there. Higher octane fuel will improve mileage by changing the timing to more advanced, (this can cause pinging on 87 octane fuel, but will not on 91 octane fuel, so you will make more power per gallon by leaning out the fuel and changing the timing. Your 'Box;' probably is set up to save fuel - but only when running 91 octane.Because your 80 gallon tank is good for about 500 miles at 6 MPG, you will need to take a couple of long trips, then start filling with 91 octane (about 20 gallons at a time), use as much as you can before filling up again, to have a higher percentage of 91 fuel, and then the knock sensor should respond well to the higher octane fuel. So if you get down to 1/8 tank, you probably will still have between 10 and 20 gallons in the tank. Adding 20 gallons will bring up the average octane to about 89. Use a lot of that fuel, and add 20 - 40 gallons of 91 and your average will be close to 90, and you should see a improvement after the next tank fill.Good luck!Fred.

Just let you know your not the only one in that boat. I had a 04 SW 37c. I bought it with 17 K and traded it at 32k. My average mpg, towing a Jeep Liberty ranged between 6 &7. I checked each tankful using math not the computer readout in which It often showed one or more mpg. My unit was all stock and mileage tracked during trips from western US to Texas

Lots of people might lie about their mileage?I get about 7mpg with or without towing the CR-V, uphill, downhill, with the wind, against the wind, at high altitude with lower octane rating, etc. That's my average for 35,000+ miles.I've not tried Fred's approach, but it probably makes sense.

There are 3 things men lie about most often:1. Their golf handicap;2. How big their last fish was;3. Their fuel mileage;:B :B :B :B

6 to 7 is the most I can get with 06 Pace Arrow on W-22 chassis..

Workhorse 8.1 liter poor fuel mileage | Good Sam Community

36 Replies

dougsee3
Explorer
Apr 12, 2015
About 8000 miles (3500 no toad) about 500 miles very high side and head winds and 500 miles -10 to-25 Fahrenheit using generator.
29 fuel stops

Best 8.33 mpg
Worst 4.82 mpg
Average 6.82 mpg (34.43 litres per 100km)

It does make a difference if you fill up during only highway driving but in town looking for campgrounds, groceries, restaurants, traffic jams, border wait lineups, take a big toll on the mpg average.
jojolou
Explorer
Apr 12, 2015
I get between 6 to 8 and 7 to 7.5 mpg. is all I average when towing my Liberty, after 28000 mi. it hasn't changed.
tropical36
Explorer
Apr 12, 2015
Lmcneil wrote:
The terrain is both mountains and flatlands, but it seems there are always hills wherever you go. It got the same mileage stock before I changed anything, although I don't remember if the tailpipe had the black soot in it. I'm thinking of taking it to Banks and have them put it on the dyno and see what they say.

I assume that you're not burning oil and this black is in fact just soot.
At any rate, it doesn't sound like there's anything wrong with the rigs fuel consumption, but you might slow down for an extra mpg and save a lot of wear and tear, as well.
J-Rooster
Explorer
Apr 12, 2015
I think 7 MPG is good mileage considering what your pushing down the road.
xctraveler
Explorer
Apr 12, 2015
WE had an '04 Southwind 36E towing a Rav4. We crossed the country 8 round trips and drove to Alaska. Total mileage was 110,000. This was over 8 years on a well maintained Vortec 8.1 L with the ally 5 spd. I logged every gallon of fuel purchased and mileage at fillup. The long term average mpg was 6.5. The first 3 or 4 years we drove the speed limit as fast as 70. The rest of the time we agreed to limit our speed to 63 regardless of any higher limit.

DW and I share the driving equally, if I had to bet she got 7 and I got 6 mpg, she has a lighter foot and I am more likely to stick my foot in it when i want to accelerate. Nonetheless the average is taken over 110,000 miles in all conditions. On good days I might see as much as 8 and headwinds heading uphill all day it might be as poor as 6. As they say YMMV
Lmcneil
Explorer
Apr 12, 2015
The terrain is both mountains and flatlands, but it seems there are always hills wherever you go. It got the same mileage stock before I changed anything, although I don't remember if the tailpipe had the black soot in it. I'm thinking of taking it to Banks and have them put it on the dyno and see what they say.
tropical36
Explorer
Apr 11, 2015
Lmcneil wrote:
I have a 2005 Fleetwood Southwind 37c with the 8100 Vortec V8 with an Allison 5 speed transmission with 28000 miles that gets very poor gas mileage, about 6 mpg towing my boat or pickup and 7 mpg empty. I tried the UltraPower chip which seemed to do almost nothing and then installed the complete Banks system (headers, muffler, exhaust, Ramair, and the Auto power tune. A little more power, but still the same fuel mileage. This is driving between 60-65 mph. The boat weights about 3700 lbs and the pickup about 5000 lbs. I read about guys getting 8 to 8.5 while towing and even better empty. The motorhome seems to have adequate power, but still will not run with the Ford 3v V10. There are no trouble codes on the engine or powertrain modules. I do notice that the inside of the exhaust pipe is jet black and rubs off on your finger. The Fords exhaust I looked at are clean and only a very little brown on your finger. I have not checked any other Chevy 8100's. The motor starts and runs perfectly and outside of the super noisy thermostatic fan and the poor fuel mileage the coach drives and runs very good. Any help would be appreciated. Thanks.....

What kind of terrain are we talking here and most usually bragging rights of 8 or more mpg are on the flats. I've gotten as much as 9 on flat land with no head wind, not towing, no generator, and at about 52 mph, which is my normal speed when driving a behemoth of sorts.
Does sound like your engine is running rich though, so that would account for some of it. Are ya sure that all these mods you speak of hasn't changed things with the computer and it's sensors?
mci7
Explorer
Apr 11, 2015
Always love the discussion at the fuel pumps, about half have a clue what their fuel mileage is, the remaining 50% range from wild to stupid guessing. Always love the ones with the 17-18 mpg on their V-10 Ford motor home, I always tell them they have a serious problem as everyone else with that setup is getting 22-25 mpg, so hope they get it fixed.
Me, I get 8.2 leaving and 8.6 returning, so my average is 16.8 mpg.
Lots of humor.
Dave M
Belgique
Explorer
Apr 11, 2015
Just a thought. My V10 mileage went in the toilet...cut in half...7 to 3.5. Took it to a chap and he said: "Front O2 sensor". When they go bad, they keep "asking" for fuel long after it is needed. Changed the O2 sensor and mileage is back to 7.
BurbMan
Explorer II
Apr 10, 2015
Bird Freak wrote:
I doubt your Burb is the same.:R

Mileage may not be the same but the engine is....unless GM creates a different tune for RV chassis that causes it to run richer and create a sootier tailpipe than the same engine does in a pickup or SUV.