Gas Mileage

[fmattox73]

What kind of gas mileage could you get with a 37 foot fleetwood motor home with a:

454 Chevy Engine
Allison Transmission
Tag Axle.

Are we talking 4 mpg, 6 mpg, or possibly 8 mpg.

I'm just looking for an approximation under normal conditions as I have never had this rig on the road for more than a few miles at a time.

Frank

[tropical36]

fmattox73 wrote:
Tropical36: You're probably right. Somewhere in the literature, I thought that I read that it had the Allison Transmission. Since you brought the subject up, I thought that I should go back and look at the Factory Manual for the chassis.
In the 7th chapter on transmissions it calls it a Hydra-Matic 4L80-E.

So nothing special other than it shifts just fine.

I've been under it once or twice and I seem to remember that it had a coil spring front end suspension.
When I got it and drove it back to the house all the tires were low, but other than the front end feeling a little loose it was fine.

Since then I've pumped the tires to 90 psi and now I seem to have a wobble at about 40mph.
Looks like I might need some front end work also.
On the other hand since I brought it home a local shop has replaced the Hydro Boost Unit, The Power Steering Pump, and the Master Cylinder. I want to check underneath and make sure that they bolted the steering gear links and arms back solidly before I have any expensive work done to it.

Frank

Best to replace the front coils if they're still OEM with airbags and get some Henderson super steers under there, according to the actual loaded front end weight. You'll need proper ride height of 1 1/34 - 2 1/2" for alignment, anyway and who wants to be replacing air bags on a regular basis anyway.
Wobble is most likely cause by tires that are out of balance and with excessive play, I'd be looking at the bell cranks as well.
As for as I know, the hydro boost for the wheel brakes and the power steering pump are one and the same thing.
By the way, check the DOT number on the tires for age (last four digits) and since you don't know the history, I'd change them out and even if they might only be 4 or 5 yrs old and you can always use them on the rear, if they're not too old, like between 7 and 10rs and dependent on a professional inspection.

[fmattox73]

Tropical36: You're probably right. Somewhere in the literature, I thought that I read that it had the Allison Transmission. Since you brought the subject up, I thought that I should go back and look at the Factory Manual for the chassis.
In the 7th chapter on transmissions it calls it a Hydra-Matic 4L80-E.

So nothing special other than it shifts just fine.

I've been under it once or twice and I seem to remember that it had a coil spring front end suspension.
When I got it and drove it back to the house all the tires were low, but other than the front end feeling a little loose it was fine.

Since then I've pumped the tires to 90 psi and now I seem to have a wobble at about 40mph.
Looks like I might need some front end work also.
On the other hand since I brought it home a local shop has replaced the Hydro Boost Unit, The Power Steering Pump, and the Master Cylinder. I want to check underneath and make sure that they bolted the steering gear links and arms back solidly before I have any expensive work done to it.

Frank

[tropical36]

fmattox73 wrote:
Thanks for all the replies so quickly. The answers were about what I was guessing at (4 to 8mpg) depending on terrain and speed.
For the one questioner, It is a P-30 Chevy chassis and the engine, cooling system and tranny was rebuilt in 2014 and a SWAG on the mileage on the engine is about or less than 6k miles. (The odometer doesn't work any more, Something else to fix.)

I came into possession of this thing through a fluke and I'm trying to figure out if it's worth keeping and throwing some money into or just donating it to some charity and taxing the tax deduction.

The previous owners seemed to take very good care of it, but again it's 24 years old. I have ALL the maintenance and repair manuals for just about every thing in it. And I'm mechanically inclined, but I'm 75 years old and wondering just how much to try to bite off with this project.

Frank

Just so you know, my question about the rare P12 chassis came up when you mentioned having an Allison transmission, so if it's actually the common generic P30 chassis (P32 actually) and no one has modified it, then I would suspect that it has a GM tranny and in some form of a turbo 400. At some point, overdrive and electrionics was added and it was then named the 4L80E and later the heavier 4L85E was introduced.
May I ask if you have coil independent front suspension or a straight axle, so that we might be sure of the chassis model?

[carp65]

when asked about gas mileage my pat answer is "I didn't buy it for gas mileage"
Too many variables effect the mileage, wind, terrain, speed to name a few.
Have been full-timing for 10+ years. We also often run our generator while on
the road to have A/C. Dash air will not keep us cool at 90+ degrees outside.

[fyrflie]

Unfortunately, most folks are using their onboard electronics to guesstimate their fuel economy.

There are simply too many variables involved.

As is the case in my MH. The speedo reads about 3 mph faster than what I am traveling. Confirmed by GPS. So, do I adjust for this when calculating fuel mileage? No

I calculate the old fashioned way. Total miles driven divided by the amount of fuel I pump into the tank.

I average about 7.5.

The bottom line is that I am smiling anytime I'm in my MH going somewhere.

[fmattox73]

Thanks for all the replies so quickly. The answers were about what I was guessing at (4 to 8mpg) depending on terrain and speed.
For the one questioner, It is a P-30 Chevy chassis and the engine, cooling system and tranny was rebuilt in 2014 and a SWAG on the mileage on the engine is about or less than 6k miles. (The odometer doesn't work any more, Something else to fix.)

I came into possession of this thing through a fluke and I'm trying to figure out if it's worth keeping and throwing some money into or just donating it to some charity and taxing the tax deduction.

The previous owners seemed to take very good care of it, but again it's 24 years old. I have ALL the maintenance and repair manuals for just about every thing in it. And I'm mechanically inclined, but I'm 75 years old and wondering just how much to try to bite off with this project.

Frank

[J-Rooster]

I agree with 6 to 8

[Tal_IL]

We had a '94 Fleetwood Flair 33 ft with 454. GVWR of 16,000 lbs and I towed a Ford Ranger pickup about 2/3 of the time. Driving was all midwest, mostly interstate, no mountain travel.

I kept a log of my mileage/gas for the 5 seasons we had it. Over the 12,000 plus miles we put on it we averaged 8.2 mpg.

[usersmanual]

I drive a 37'7" Gasser, 8.1L Chevy engine allison Tranny

Originally I towed a 4,000 Pound (max tow for this RV) Chevy Lumina APV with Axle lock (It is a true trailer when towing) 8 mpg 9 with a fresh wax job.

Car died of old age I hit 11MPG with a fresh wax job

11 ??? in a almost 38 ft gasser? you must drive down hill most of the time

9MPG towing a 4K tow vehicle? (highly unlikely )

[wa8yxm]

crasster wrote:
I don't see why it wouldn't get 7-8mpg.

I drive a 37'7" Gasser, 8.1L Chevy engine allison Tranny

Originally I towed a 4,000 Pound (max tow for this RV) Chevy Lumina APV with Axle lock (It is a true trailer when towing) 8 mpg 9 with a fresh wax job.

Car died of old age I hit 11MPG with a fresh wax job

New towed is a 2500 Pound Dodge Neon with Trans Lube Pump.. Tows a bit heavier 7.5 to 9, add a MPG with fresh wax.

Any question why I wax 2x a year (Before my major migration trip?)

[tropical36]

usersmanual wrote:

Anyway, in top gear on the flats, not towing and no wind, running about 55mph and not counting the genset, I would expect you'll see about 9mpg.

maybe in your wildest dreams;;; more like 7.5 MAX

Wellllllllllll, I was estimating this, based on what he's driving, comparing it to what I was driving for nine years and to what I'm driving now, which is over 40ft, GVWR at 34K lbs and with a computer doing the calculations for me. Since I've owned it for the last 5 mons, it hasn't wavered at 6.1 overall. I assume this isn't just me, either and is taking it's whole life into account, as well. This being the case, it should eventually improve, even if just a little. We shall see, I guess and not even sure how the genset figures into this reading, if at all.

[tropical36]

tropical36 wrote:

fmattox73 wrote:
What kind of gas mileage could you get with a 37 foot fleetwood motor home with a:

454 Chevy Engine
Allison Transmission
Tag Axle.

Are we talking 4 mpg, 6 mpg, or possibly 8 mpg.

I'm just looking for an approximation under normal conditions as I have never had this rig on the road for more than a few miles at a time.

Frank

Are you saying that you have a rare P12 chassis here?
Didn't know that they made anything longer than 36ft on any of the Chevy chassis's either.
Anyway, in top gear on the flats, not towing and no wind, running about 55mph and not counting the genset, I would expect you'll see about 9mpg. Over the yrs and counting different terrain, idling, traffic stops with gear changes, about 7.5 overall.
Whatever it is, it's not significant over the cost of ownership, like depreciation per mile might be with the newer rigs.

I should probably mention that the best way to lessen your fuel costs and in effect increase your MPG, is to stay overnight in a Walmart, when feasible.

[Gjac]

A lot depends on the weight, gearing, and how you drive, but at 37 ft with a tag axle you might weigh 20,000 lbs or more. You are more likely to average below 8 mpg. I have a 33 ft MH with a 454 TBI and a 4 speed transmission that weighs about 15,000 lbs fully loaded (13,500 ULW) and have averaged 8.6 MPG over 85,000 miles of travel.

[haydoracin]

usersmanual wrote:

Anyway, in top gear on the flats, not towing and no wind, running about 55mph and not counting the genset, I would expect you'll see about 9mpg.

maybe in your wildest dreams;;; more like 7.5 MAX

On the trip referenced in the post above I recorded three tanks at or over 9 mpg all across NM, AZ and Texas. These were not consecutive fill ups but the other fillups were in the 8s.

I don't think I was dreaming all across those three states.

Haven't experienced that before or since but we will see what happens on this winters trip since the tune up.