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.....

[Bird_Freak]

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

Same as mine. OP is not going to do much better.

[GREGORYJ]

Our last falls trip was 5100 miles. Divided by total gallons purchased the
mileage was 7.7 mpg. That included city traffic , generator use, etc.
Speeds were 60 - 65 mph. Our toad is light , 1800lb. Smart car.
I know lots of times I see the inst. mileage display showing better , between
8 & 10 mpg, but after the trip is over, the miles driven and gallons used tells the
real overall average.

[DSDP_Don]

There are four types of people when it comes to reporting fuel mileage. You have the guy that only tells you his BEST mileage he got once in five years of ownership. Then the guy that estimates his by figuring he used a 1/4 tank and went 150 miles so he must have gotten "X" mpg. There is the plain old bull crapper and lastly, there is the guy who puts pencil to paper and actually knows his true mpg and tells the truth about it.

Poor mileage is also seen if you're the type that takes a lot of short trips. Short trips that take you on and off the freeway, up grades and through towns will always get you poor mileage. If you drive 300 miles on a the freeway with maybe one hill climb, you'll get better mileage.

You say you're doing 60-65....is that true or is it 65 plus a smidge. That's going to eat fuel. Lastly, that engine is a beast with the Allison attached. No way you shouldn't be blowing past Fords, similarly loaded.

[Gjac]

What is the total wt of your MH? When people state MPG they don't state the Wt of the MH. I averaged 8.7 mpg over 80k miles on an old 454 eng with a 4 speed trans. On the surface that sounds good but the MH only weights 13,500 unloaded and 15,500 lbs fully loaded. Your's probably weighs close to 25 k fully loaded, which is a big difference. Adding headers,FF mufflers, CAI, did nothing to improve MPG either only performance. Changing to syn oil did not help mpgs either. There are two things that helped MPG one was advancing the timing from 4 degrees before TDC to 9 degrees before TDC. This added about a .2 mpg increase. The other was installing an old vacuum gauge I had laying around. The higher the vacuum the better the mpg's. Also it allows me to stay in 4th gear when climbing a hill by letting of the throttle. I have gotten as high as 12.6 and as low as 6.6 mpg. If I keep the speed down to 55-60 and watch the vacuum gauge I frequently get over 9 or 10 mpg but overall it is 8.7. Try slowing down a bit and your MPG's will increase.

[frankdamp]

Our V-10/F53 Georgetown 32-footer (an '02) got a consistent 7.2 mpg over the 6000 miles we drove it. The good thing was, it didn't change with altitude, thanks to EFI. By comparison, our previous 1985 26' Class C, with a 460 (carburated), got 6.5 at sea level and about 4.5 at 2000 feet. We have a lot of high altitude roads around here - Washington Pass on SR-20 is 5200'.

We didn't tow anything with either rig.

[BurbMan]

I would start with the basics as was mentioned, replace the air filter and fuel filter.

The other thing to check is the MAF sensor. It sits in the intake airflow between the air filter and the intake manifold and measures incoming airflow. The PCM uses that info to determine fuel delivery, and if dirty, could result in the engine running rich, which would explain both the low mileage and the black tailpipe.

The MAF is easy to remove but it is delicate. Be sure to use the aerosol MAF cleaner, NOT carb cleaner, or Brakleen or other chemicals. Take it out, spray it, put it back in after it's dry.

You might also consider plug and wires...even though you only have 28k miles, those parts are 10 years old now, and wires can break down due to heat cycling and cause a weak spark, which could cause incomplete combustion and also blacken the tailpipe.

No codes set because nothing is "broken", only little things that are each taking their toll and adding up to a 1 mpg or so cost.

FYI, I have 160k miles on my 8.1, and averages over the years have been 11-12 on the hiway, 10 around town, and about 7-8 towing. I have found that mileage has improved 1 mpg across the board since I changed to Mobil 1 Hi-Mileage oil last year.

[nevadanick]

8.1 in small class a towing 8.5 x 20 enclosed trlr with same Banks stuff and same results as you including black exhaust. I have been as low as 4mpg

[Tom_N]

I have a 2005 Itasca Suncruiser 38R on a W24 chassis. I bought it new, a factory order. I weigh 23,200#s loaded. 32,100 miles. I towed a Honda Civic about half of these miles.

I've averaged 6.97 mpg since new. I mostly keep my interstate driving speed at 60-63 mph. I use cruise control.

-Tom

[moisheh]

Lots of fairy tales when it comes to MPG. But have you hooked up a scan gauge to see if there are any trouble codes? maybe have a good shop have a look. You still will not get 8 plus mpg!

Moisheh

[tinkerer]

It's just you are an honest guy quoting gas mileage in the real world. There are so many factors determining gas mileage on a motorhome. The wind is a huge factor and whether you are going up or down in elevation. With my DP pulling a 6000 lb load in all honestly I only average about 7 driving 65. One day heading east out of Flagstaff I averaged 11.5 driving 70 mph. That is with a strong tail wind and going down in elevation. So I could brag that I get 11.5 mpg when in reality it was only one day under special circumstances. 😉

[rgatijnet1]

The easiest way to increase your fuel mileage is to tow another vehicle. That way you get TWO vehicles from point A to B with very little effect on the fuel used. I get 14-16 combined MPG with my 8.1 towing a Chevy HHR. :B

[s_N_s]

You didn't mention your driving habits. Do you use you cruise in hilly terrain? That will cause a lot of downshifting of the trans and of course a higher rpm range which in essence eats more fuel. I average between 7 - 8 mpg and am happy with that. As far as keeping up with t a V10, you shouldn't be having any problem with that either all things being equal. Lastly I don't think we purchase these things for there fuel mileage. Good Luck, hope things pickup for you but seriously between 7 and 8 is going to be the best it will be.

[Randu]

Your mileage sounds about right. 8.1 in my 2004 2500 pick-up when pulling 16,000# 5th wheel was 7-7.5 under good conditions but about 6.5 if winds were bad or hilly. Truck empty in town about 9 and 11 empty on highway. Plenty of power but thirsty. Randu

[Mike_Hohnstein]

35 years of towing the race car, every thing from a 1/2 ton 74 Chevy w/8' camper to big rig diesels. Worst was 78 3/4 ton 400 small block chevy, manual trans, 10.5 camper and 22' enclosed trailer got 3.5 mpg, every thing else and I mean every thing got 6.5 to 7, even the 34.5 Airstream towing a 240D. All the gassers except the sbc were 454s with T.400s. The diesel rigs get the same even though they weigh 3 times as much.

[viajante]

You might also think about replacing the fuel filter. I changed mine at 25K and it made a significant difference.