So yesterday I had to do a 160+ mile trip RT. I had an interesting set of conditions which prompted me to try this out.

1. I was late leaving and had a 1/4 tank of gas which made me nervous about having enough to get there so we stopped at the Turnpike gas station to get $10 worth gas with the idea of filling it up later on where it was more reasonably priced. Well the gas station was poorly manned and it was clear that we were going to have to wait a long time so we decided to try and make it with the gas we had. That meant watching the consumption carefully. I was pleasantly surprised because due to conditions and traffic we were able to keep it at 65 mph the entire way and I got some of the best mileage ever in that car. Better than even some of the long trips. I saw 23.4 for a while and in the end we averaged 23.1 mpg which for a STR around here is really good.

2. So after my appointment I decided to use this as a test and I went into Pennsylvania to pickup a tankful of pure gas and drive not quite the exact same route back but it did include all of the route out there as well as the foray into PA for the gas. The gas was $.50 a gallon more but some of that is the PA pricing differences. We had a 1/4 tank of the ethanol blended gas still in the tank which is 10% alcohol here so that's a net of 2.5% when you add in 3/4 of a tank of pure gas.

So the result?

I saw 27.4 mpg most of the way, 27.8 for a little while and my conclusion is that this netted 4 mpg better milage.

With all pure gas it undoubtedly would have been even better!

Why it the hell are we screwing up our gas like this????

15% is just nuts!

 

power, money lobbying .... turning food into gas is something like the most dumbest thing any human being EVER came up if, except for maybe Arm & Hammer convincing people to buy their product to pour it down the drain to get rid of some perceived smell.

Less energy in E90, 85 etc per gallon than pur fuel, plain simple. To get as far in E90 as with pure fuel you have to burn more gallons.

Simple.

The farmers dig it though, guaranteed market and price stability ....

 

Maybe also some sort of hope to reduce or eliminate dependency on foreign oil.

All disguised as saving the planet (*), too, I think.

(*) the planet will be fine, but we humans may not, is what is actually meant so why don't they just say that???

hmm, those figures would make me wonder if I could pay a small premium to get alcohol-free fuel

 

Your figures suggest that going from 10% ethanol down to 2.5% gave approx 15% better mileage.

Even if ethanol contained zero energy and passed through the engine contributing nothing, at a 7.5% concentration as in your example it could not affect mileage by more than that same percentage.

Yes, ethanol blended fuel is as big a charade as I've ever seen in the car industry, but facts is facts. It has 70% of the energy of gasoline, so at a 10% concentration (E10) a given vehicle will return 97% of the mileage of pure gas. Most people don't notice a 3% variation in mileage.

 

I'm just reporting the data from the Jag's computer.
It was all highway driving.
If anything I tried more to conserve on the first leg of the trip.

So maybe there's something more going on here than we know?

 

Ah. Individual readings from these instruments don't mean much when abbreviated distances and times are involved.

I've seen bigger fluctuations on mine without changing gasoline types.

For reference, I frequently see 30+ mpg on my non-R while using E10.

 

Glad your gas test worked out! I had my gas light come on the other day on my way to work. I only had about 20 miles to go so I thought no problem, the light just came on, I can easily go another 30 miles! Well about 15 miles later with only 5 to go, even though my fuel thing said 15 miles to empty, car ran outta gas..... Ugh I was so mad! Every car I have ever owned prior to this one I have driven with it saying zero miles till empty! Lol.... Oh well, lesson learned with the STR! When the gas light comes on I'm filling up! Not taking that chance again

 

Running that low on gas, you also run the risk of the jet pump and fuel pump to malfunction. They are both inside the tanks and rely on the fuel to keep them cool and operable. I had first hand knowledge of this problem (idiot previous owner) and lucky the repairs were warranty covered. Otherwise, if you're not a DIY, it'll cost anywhere from ~$800.to ~$1,000 to fix at a dealer.

 

The computer measurement is still a valid indicator that there was a "relative" improvement.

Some additional factors that can come into play:

1) the outbound trip may have been uphill while the return trip was downhill;

2) if the pure gas was also a higher grade, then the ecu is able to push the
ignition advance further which would also net more mpg;

3) some stations have been known to push the ethanol over the 10 percent advertised
by several points ... ethanol is cheaper.

 

That would be Imperial gallons? The 25 percent bigger ones?

 

US gallons.

 

They're not 25% bigger, just 20%, apparently.
https://www.wolframalpha.com/input/?...ial+gal+to+gal

 

80 miles on the way out. 120 miles on the way back.

elevation change on the way out 300ft - 80 ft so about 220ft

elevation change on the way back 500ft - 80ft so 320 ft.

So yes a slight incline is involved. I don't think that explains it.

Both pumps stated 91?

I'm as surprised as anyone by this. I frankly wasn't expecting such a big bump in MPG but it's real.

 

My fool light never came so it's not an issue.

There's about 2 to 2.5 gallons in the tank when it reads completely empty. But I don't know if it still runs at that point or not?

 

Umm, no. You're expecting laboratory grade precision from instruments that are not much more sophisticated than a wooden dowel used as a dipstick.

If the presence of ethanol was the sole reason for the difference in the mileage and all the gauges were accurate, the old fuel would have to have been spiked with 40-50% ethanol to achieve such a boost with the new fuel. I highly doubt even the conspiracy theorists would contend that this happened.

Try a little more experimenting. Reset the mpg calculator at random intervals and take a note of the inconsistent numbers it comes up with after just an hour or two of driving.

Edit: forget to mention that the 30 mpg (US gallons) I can induce is also possible with 87 octane fuel.

 

Another factor could be the PA gas was new summer blend and what was in your car was NJ winter blend----could be 5-10% difference in energy content there.

 

A 4.2L engine giving 30 mpg (US) on 87 octane stretches the imagination every bit as much as a 4 mpg increase using plain gasoline compared to E10.

It should be noted that that under poor housekeeping conditions, a gallon of E10 can contain 8 times as much dissolved water as a gallon of plain gasoline. Still shouldn't explain a 4 mpg difference, but definitely won't help.

 

Wow there sure are a lot of people trying to come up with something?

This is an experiment I can't possibly repeat all that easily but if I do get another chance I'll try it again.

This was over a pretty decent interval of road and a couple hundred feet of elevation doesn't explain this.

I've never ever seen that sort of mileage for a run of 120 miles (return trip).

It wasn't terribly windy either.

The winter versus spring gas formulation is not one I had heard could have an effect on mileage? What's the basis for this idea? Remember, there's no alcohol at all 365 days a year in this particular fuel.

 

Also remember that I got terrific mileage (for my experience with this car) on the way out with the E10. Traffic was very accommodating in that it was smooth even if most of the way it was not possible to exceed 65. I wonder if this car also gets substantially better mileage at 65 versus 75 my and most peoples prefered cruising speed. I tried to maintain that pace on the return trip but I know I was faster a lot of the time.

How does 87 octane have anything to do with this? I'm not following ...

 

And here is the 'proof' presented yet again.

https://www.jaguarforums.com/forum/s...e4/#post663803

Staatsof-

The relevance of the octane is a long-standing disagreement over the side effects of using less than (or higher than) recommended octane levels. The sky is not falling there either.