Workhorse 8.1 liter poor fuel mileage

[Lmcneil]

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.....

[dougsee3]

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]

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]

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]

I think 7 MPG is good mileage considering what your pushing down the road.

[xctraveler]

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]

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]

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]

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]

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]

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.

[rgatijnet1]

If you have an OBDII gauge, you can monitor the air/fuel ratio. If it is 14.7 when in a normal cruise, that is about as good as you are going to get. Your A/F ratio will change during hard acceleration or climbing an incline but the 14.7 is considered an optimal A/F ratio where the 8.1 is not running too lean or too rich.

[Bird_Freak]

BurbMan wrote:

Bird Freak wrote:
OP is not going to do much better.

The fact that OP has so much soot on his tailpipe says something isn't right, mine burns nice and clean. And whatever that something is surely has an effect on mileage.

I had almost the same coach in the Pace Arrow so I speak from experience. Bought it new and that's about the mileage I got. I doubt your Burb is the same.:R

[BurbMan]

Bird Freak wrote:
OP is not going to do much better.

The fact that OP has so much soot on his tailpipe says something isn't right, mine burns nice and clean. And whatever that something is surely has an effect on mileage.

[chuckftboy]

My coach is 26,000 lbs loaded and towing, gets 6.5 mph at best
My Jeep is less than 1/6th of that and gets 14.5 mph average
If you look at it that way "mileage ain't so bad" on the coach
Black, sootie, tail pipe is a sign of running rich. Need to check the fuel to air ratio. You may be waisting some fuel that you could save if it ran leaner.