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.....

[RCMAN46]

When was the last time you replaced the air filter?

[Janss]

I have the same engine and transmission. My last three summer trips of 3000-4000 miles resulted in average mpg of 7.31, 7.33, 7.70. That was with the toad.

[dcbrewer]

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

[topflite51]

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

[Pangaea_Ron]

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.

[emorris548]

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

[Golden_HVAC]

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.