I always seem to average right around 8.5 mpg however the return leg of this last trip I saw averages around 7.5 and that concerned me. I'm looking for reasons this could have happened.1) The return leg used 10% ethanol gas during 7.5 and no ethanol during 8.5 legs - could that be the difference?2) I worried I had a stuck caliper (Workhorse brakes - but my VIN is exempt from the recall). However, after 70 mi, the rotors/calipers were near ambient air temperature. No mushy brakes and no "burning" smells either.3) Headwind? There was wind from the drivers side, straight into the MH (not tail or head).4) I tow a CRV - verified no wheels locked, no parking brake, everything looked perfectly normal there. No hot wheels.5) I drive at a constant 63mph (towing max on the CRV is 65), that gives a pretty constant 2200 rpm (varies with hills of course). This was constant during times of low mpg.6) It was very hot outside - but using engine A/C did not make any difference in mpg reading.7) I did look at instantaneous mpg and on level road it varied a lot: low of 6.0 high of 10.2 and it was jumping around erratically. Made me wonder if the "mpg" computer was accurate. However, it seems as though I did use more gas on the return leg than normal so I suspect the lower mpg was real.Could there be anything with the engine that I should check? It ran and sounded just fine. Lots of power as always. No funny noises.The autopark brake was performing normally. I could coast down a slight hill with engine in neutral (ie, autopark brake was not dragging) and when the autopark was engaged, the MH would stop almost instantly.I'm at a loss for any other ideas.... what should I check to explain the lower mpg?

Alfred622 wrote:1) The return leg used 10% ethanol gas during 7.5 and no ethanol during 8.5 legs - could that be the difference?There's yer sign!!!:BHappy camping!!! See y'all down the road!!!:)

Do you have the 8.1 chev or the ford V10? How did you determine the MPG? Did you fillup and write the odometer reading down and then after driving that leg of the trip, fill up again and do the math, miles driven divided by gallons used?? On board cumputers are just a reading of present fuel use at the time, not an overall fuel use over many miles. My 8.1 Chev gets about 7.5 all the timetowing a CRV. I have never got 8.5.

If you use ethanol your mileage will always be less then regular. This is the ugly truth that ethanol people always try to hide. We are work camping in a so called green state where you can't buy regular gas, everything has ethanol in it so we are buying more because our mileage is way down on our Jeep. When summer ends we will be back in a state that we can buy regular and our mileage will go up again.

As a tree hugger, I'm trying to get you down to 3.5 mpg. I'll have to work harder! LOL! Jus kid'n.I think one mile per gallon is not enough to worry about. There are so many factors that could make a difference. Look at the long-haul average.Safe travels,MM.

Ideas Needed: Why sudden drop in mpg? | Good Sam Community

427435
Explorer
Aug 31, 2013
philand wrote:
427435 wrote:
philand wrote:
copeland343 wrote:
ethanol
Ethanol has only 1/2 the btu as gasoline, so 10% ethanol will give you 5% mileage penalty. I used to travel w/ guys who raced outboards. We used 100% ethanol and had to rejet carbs. BTW, I think the farmers brought us ethanol along with a guy who owned a big distillery. I don't think even the tree hungers could come up with a more destructive idea.

That's wrong. Ethanol has 2/3 of the BTU's of gasoline.

http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
If you read the referenced information, The CGE of ethanol(i00 %) Is slightly less than half of the energy of std. gasoline. The octane is higher allowing higher compression without detonation.

Look again. Pure ethanol has 66.67% of the BTU's of base gasoline------or it takes 1.5 gallons of pure ethanol to provide the same BTU's of a gallon of pure gasoline.

Thus, a gallon of fuel that is 90% gasoline and 10% ethanol will have 96.67% of the BTU's of a gallon of pure gasoline.
cbr46
Explorer
Aug 30, 2013
2002 Fleetwood Terra 32 w Ford 2V V10

Coming home from purchase we got 8.0 interstate then 8.5 mpg on a later fillup. The latter was all off interstate.

I got 6.4 and 6.8 on a recent trip to FL. YIKES! Both fillups were in GA. This trip added a 6x10 cargo loaded at 2300 lbs. 3/4 tank water, others empty (fresh to grey variation on return trip). Typical speed 65 mph, lots of rain on return. Some generator use while camping but not during driving.

On the way back my knee was aching so I let cruise control do some of the work. About 5.4 mpg (uphill) it would downshift to 3.5 mpg and less, and do that with half the overpasses. That's a lotta gas! Bad move.

I did notice it would jump up to 10+ mpg following tractor trailers. Wouldn't want to do that for any time (don't think the t-t drivers like it either).

I might have to start driving slower . . . . . not sure that's possible. 65 is pretty slow when you want to get there.

How much would anyone suppose the 2300 lb 6x10 cargo trailer is pulling us back?

I do have a slight drag on RF brake caliper . . . . enough to make a noise when pulling in for fuel, etc but not enough to smell any heating. (will be fixed).

There's also considerable wheel imbalance, we think on the front.

All tires inflated to 110 psi (DynaTrac Tires). Rears are all terrain, fronts are steers.

Best,
- c bob
johnwalkerpa1
Explorer
Aug 30, 2013
I may have missed it in all of the other discussion, but to the OP: How many miles are you talking about when describing the legs of your trip?

I wouldn't even worry about a drop from 8.5 to 7.5 over 1 or two tanks of fuel since that can easily occur and probably only indicated a change in one of a hundred variables.

However, I would be more concerned if it was an average drop over say 5000 miles.
philand
Explorer
Aug 30, 2013
427435 wrote:
philand wrote:
copeland343 wrote:
ethanol
Ethanol has only 1/2 the btu as gasoline, so 10% ethanol will give you 5% mileage penalty. I used to travel w/ guys who raced outboards. We used 100% ethanol and had to rejet carbs. BTW, I think the farmers brought us ethanol along with a guy who owned a big distillery. I don't think even the tree hungers could come up with a more destructive idea.

That's wrong. Ethanol has 2/3 of the BTU's of gasoline.

http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
If you read the referenced information, The CGE of ethanol(i00 %) Is slightly less than half of the energy of std. gasoline. The octane is higher allowing higher compression without detonation.
427435
Explorer
Aug 26, 2013
Patrol 65 wrote:
Have you tried changing the air filter on the engine?

Unlike the old days of carbureted engines, a dirty air cleaner won't hurt mpg-------only hp on a fuel injected engine.
427435
Explorer
Aug 26, 2013
Snowman9000 wrote:

Oil companies are not fond of it, regardless of being able to increase octane with it.

There is a very good reason the oil companies don't like ethanol. For every gallon of ethanol that is used, about 2/3 of a gallon of gasoline is no longer needed. That is one of the reasons (not the only) that gasoline now costs less than diesel.
Patrol_65
Explorer
Aug 26, 2013
Have you tried changing the air filter on the engine?
427435
Explorer
Aug 25, 2013
wallynm wrote:
higher octane hence less knock but less or fewer Btu's per gallon hence less MPG

427435 wrote:
I think your understanding is wrong---------at least in Minnesota. Actually, ethanol makes it easier to rate a gas as higher octane.

I'm not sure what you're saying here. E10 at 87 octane has the same octane as regular gas at 87 octane but about 97% of the BTU's. Premium gas has 91-93 octane and approximately the same BTU's as regular gas. Premium gas, however, allows more compression before pre-igniting.
427435
Explorer
Aug 25, 2013
philand wrote:
copeland343 wrote:
ethanol
Ethanol has only 1/2 the btu as gasoline, so 10% ethanol will give you 5% mileage penalty. I used to travel w/ guys who raced outboards. We used 100% ethanol and had to rejet carbs. BTW, I think the farmers brought us ethanol along with a guy who owned a big distillery. I don't think even the tree hungers could come up with a more destructive idea.

That's wrong. Ethanol has 2/3 of the BTU's of gasoline.

http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
427435
Explorer
Aug 25, 2013
Coyote74 wrote:
While on a rv trip in july, in nj I refueled our HHR towed at a sunoco on the garden state parkway I was getting 31 mpg before refueling (normal). Once I refueled mpg dropped to 24 mpg . Drivin habits and the terrain the same. Brought it back to nc and still 24 mpg. Refueled a week later in charlotte area and same 24 mpg. A week later refuled in mooresville, nc and back to 32 mpg. Sunoco and shell, and sheetz gas. Weather the same rain some sun at times and very humid. The research octane rating at tbe pump sucks. They have no ideas of mixing ethanol properly, I think its manipulated by who's running the mixing valve at the refinery or who's asleep at the valve. Ther probaly sneaking in loads of E15 with the E10 at the pumps for testing resuts for future.

Sounds like you filled up with E85-------not E10. No way that 10% ethanol could reduce your mpg that much IF everything else was equal.

Forum Discussion

Ideas Needed: Why sudden drop in mpg?

About Motorhome Group

Related Content

Need ideas

need ideas for strange problem

Clever storage ideas needed

heat ideas

Bounder with with sudden electrical problems