Fuel for Gassers

[Alex_and_Tee]

Anyone run Premium fuel or Octane Boost? Improved performance/mileage or waste of $$.

[Rick_Jay]

JaxDad,

I realize that. Just being a bit sloppy. 🙂 I was including various situations in one set of rounded numbers: towing/not towing, generator use, different seasons, etc. But high 7's to 7 is about 10%. I guess I should've said low to mid 7's on the ethanol junk and from high 7's to low 8's with real gas. That would definitely be a more accurate statement. 🙂

My highest MPG ever, on a tank of real gas, occurred on a long day trip in the Fall (no generator, no A/Cs, not towing the minivan and driving mostly level terrain) and the rig returned about 9.2 MPG over the 300 mile round trip.

Unfortunately, I only had the rig about a year or so before all we could get up in this neck of the woods was the ethanol junk, so I couldn't really get really good, seasonal data. To be honest, I didn't expect any MPG drop when they forced the E-10 on us. But sure as can be, once that was our only choice, every vehicle we owned took an MPG hit in the neighborhood of 10%. For the cars, this became obviously apparent without even measuring anything. The "low fuel" warning lights were going on with about 10% fewer miles traveled.

~Rick

[JaxDad]

Rick Jay wrote:
Ponderosa,

I'm right there with Hikerdogs and JaxDad. When we first purchased our motorhome, 10% ethanol was not common in New England. Within a few short years, it was mandated. Without a doubt, our gas mileage dropped 10% with the 10% ethanol fuel.

I used to get consistent high 7's to low 8's. On ethanol, it hovers around 7. .

~Rick

Rick, not to nitpick, but ‘low 8’s’ down to 7 is a 15% drop, not 10%.

[rgatijnet1]

On every gas pump that I have seen, the little sticker says "no more than 10% ethanol" meaning the fuel is mixed with the last batch, etc, and it may or may not have 10% ethanol. This is why your fuel mileage may vary from tank to tank. Some stations like WaWa and others have non-ethanol fuel as well as ethanol blend fuels. Some have the E85 which can be used in vehicles like my HHR toad. I always get the non-ethanol fuel for my small engines at home, including my emergency generator. In the motor home with the GM 8.1L engine, I used the E10 87 octane fuel and experienced no issues in 100,000+ miles of travel. I even used the 85 octane when in the Western mountains but always added 87 when I was going to lower altitudes. I never used any higher octane fuel than 87 and never felt the need. I didn't monitored my fuel mileage and didn't really care. Fuel costs were the price I paid to travel in an RV. To keep my in tank fuel pump cool, especially in hot weather, I always tried to refuel before the level got below 1/4. I guess it worked because I never had to change my fuel pump.

[Hikerdogs]

I've checked the mileage religiously on our 2001 Adventurer and our 2013 Adventurer. It's hard to put an exact number to the mileage difference due to the number of variables involved, but with both motorhomes we've consistently gotten 1 mph or more traveling the same routes when using the non ethanol regular. Given mileage is usually between 7 mpg and 8 mpg depending on the route traveled. An additional 1 mpg with non ethanol makes it cost effective to use it when available.

[Rick_Jay]

Ponderosa,

I'm right there with Hikerdogs and JaxDad. When we first purchased our motorhome, 10% ethanol was not common in New England. Within a few short years, it was mandated. Without a doubt, our gas mileage dropped 10% with the 10% ethanol fuel. I used to get consistent high 7's to low 8's. On ethanol, it hovers around 7.

One time, on a trip down south, unbeknownst to me, I stopped at a station and put REAL GAS into the rig. As we're driving down the highway, I checked the Scangauge MPG and the dash MPG...BOTH were reflecting around 8 MPG, plus or minus, when I had been seeing the typical low 7's the entire trip up to that point. At first, I thought I was just going down hill, but the GPS elevation proved that not to be the case.

Shortly after the next fill-up, the mileage pretty much was back to the low 7's. Once we arrived at our destination, I carefully reviewed the receipts and realized the state we had fueled in which gave the MPG boost DID NOT mandate ethanol fuels.

I know what the "science" says about the alcohol having an energy content. Of course it does. But for all of our vehicles, I've always experienced about a 10% drop in MPG when forced to run 10% ethanol gas.

Perhaps there are some vehicles that might only see a 3% or 4% drop in MPG on 10% ethanol. I have no idea. I just know that NONE of our vehicles are in that category, nor any vehicles owned by folks I've chatted with about this.

~Rick

[JaxDad]

Ponderosa wrote:

Hikerdogs wrote:
If you're looking to improve fuel mileage non ethanol regular (87 octane) is the way to go. As mentioned the ethanol does nothing in that regard except lower the mileage by the amount of ethanol in the fuel. With a 10% blend you can expect a 10% poorer mileage than with non ethanol unleaded.

It's a bit amusing that the non ethanol regular gasoline is most available in Iowa, the state that produces the most ethanol in the country. Non ethanol regular wasn't even available in neighboring Wisconsin until about 5 years ago. Even now it's not available at most stations. It's more easily found in rural areas and those catering to "recreational vehicles". In this case recreational vehicles refers to ATV's and marine inboard and outboard motors.

A 10% reduction in mileage would imply that ethanol has no available energy on combustion. In fact, it is around 3 to 4% less than gasoline. So the mileage drop in reputable testing I have seen is also 3%-4% not 10%. That is also my experience when I have experimented. I would much prefer the real thing, but with pricing what it is, it is simply too expensive for payback at that number. I use it only in my stuff that frequently sits for months unused.

The problem with “reputable testing” is that it’s just that, testing, done in a laboratory.

In the real world, where we ‘test’ our mileage going down the highway, the differences are VERY different. There is water entrainment, fuel adulteration, messed timing based on false or misleading sensor input and generally much lower performance.

The only ‘real’ way to measure fuel economy is to do large scale real world test twice, once each on 2 different types of fuel. I have done that repeatedly and the results were FAR more than 3% to 4% different.

[T18skyguy]

RLS7201 wrote:
Why does premium fuel give more mileage and power?

Richard

Matt gave a very good answer and I'll add just a bit more. When engines are new, they usually don't ping even under high load and heat. But as they age,deposits build up on the top of the combustion chamber, valves, and pistons. These deposits raise the octane requirements because they take up space, and actually raise the compression ratio and the result is that the engine starts pinging on 87 octane. On cars, you usually see it start about 30-40 thousand miles. Engineers call it "Octane creep." So if you hear that rattling sound,you can move up to 89 octane to stop it if you'd like. Even though some manuals say light pinging is ok, myself I just want it stopped. I just give it what it wants. Higher octane doesn't really give you more power, it just stops the sensors from taking away power.

[vjstangelo]

When recently in CO I noted again that their "regular" is 85 octane. Since the manuals for my vehicles state don't use less than 87, I went with the mid grade 87 or premium 91 which pushed the price to over $4 gallon.

[Ponderosa]

Hikerdogs wrote:
If you're looking to improve fuel mileage non ethanol regular (87 octane) is the way to go. As mentioned the ethanol does nothing in that regard except lower the mileage by the amount of ethanol in the fuel. With a 10% blend you can expect a 10% poorer mileage than with non ethanol unleaded.

It's a bit amusing that the non ethanol regular gasoline is most available in Iowa, the state that produces the most ethanol in the country. Non ethanol regular wasn't even available in neighboring Wisconsin until about 5 years ago. Even now it's not available at most stations. It's more easily found in rural areas and those catering to "recreational vehicles". In this case recreational vehicles refers to ATV's and marine inboard and outboard motors.

A 10% reduction in mileage would imply that ethanol has no available energy on combustion. In fact, it is around 3 to 4% less than gasoline. So the mileage drop in reputable testing I have seen is also 3%-4% not 10%. That is also my experience when I have experimented. I would much prefer the real thing, but with pricing what it is, it is simply too expensive for payback at that number. I use it only in my stuff that frequently sits for months unused.

[Hikerdogs]

If you're looking to improve fuel mileage non ethanol regular (87 octane) is the way to go. As mentioned the ethanol does nothing in that regard except lower the mileage by the amount of ethanol in the fuel. With a 10% blend you can expect a 10% poorer mileage than with non ethanol unleaded.

It's a bit amusing that the non ethanol regular gasoline is most available in Iowa, the state that produces the most ethanol in the country. Non ethanol regular wasn't even available in neighboring Wisconsin until about 5 years ago. Even now it's not available at most stations. It's more easily found in rural areas and those catering to "recreational vehicles". In this case recreational vehicles refers to ATV's and marine inboard and outboard motors.

[theoldwizard1]

I always ran premium when towing through the Smokies. No knocking !

[wolfe10]

The only real "octane" issue is if filling up at high elevation where they are allowed to sell lower octane fuel and driving on it to lower elevations/mountains.

When filling in places in the mountains, we always read pump octane rating and put in the octane called for by our vehicle. It may NOT be their regular.

[Sandia_Man]

We pretty much use the cheapest unleaded fuel available at the pump wherever we happen to be, sometimes 85 octane at high elevations, mostly 86 is what we normally pump in our neck of the woods. We do occasionally add octane booster to a tankful, and it sure does have a positive influence on the miles to empty info from dash display, although from our experience it is wishful thinking on the ECUs part, just a minimal power boost noted.

We have plenty of power and we do traverse many inclines to get to where we are going, which is routinely at high elevations where gassers lose significant power. Now, if we had any performance issues we would get premium, thus far our 40' Monaco gasser is taking the hills using plain ole regular. For our sports cars we use premium as they just flat out perform better, our SUVs, full-size vans, and HD trucks all get regular unleaded.

[Matt_Colie]

RLS7201 wrote:
Why does premium fuel give more mileage and power?

Richard

Richard,

This is a very good question, and I will try to answer it without getting too "engineer" for you.

In times past, engines did not have a computer to control fuel mixture and ignition timing. Now many do.

They listen intently for any knock that is the result of wrong conditions including spark timing. When they hear a knock, the box will start a bunch of corrections that some engineer has tested and advised. Usually the cure is to back off the spark timing. While this will cost some mileage, because the ECU (Engine Control Unit)never gets tired of listening and gets board at sitting still, when it hasn't hear a knock in a while, it will dial in more timing advance. It may also lean out the mixture a little (he can also use fuel to quell a knock). Another correction that many ECU have is to lower the engine temperature. There is not a great deal he can do here, but it is again involved with fuel mixture and sometimes the engine fan speed control.

When you have your very own computer and a raft of sensors, you can pull off all manner of nifty things.

If I lost anybody in here, come back and I will try again.

Matt