Fuel Observations

[slomove]

While I was out to Wyoming and South Dakota, I obviously had to fill up with the local gas. I did notice 3 major differences:

 

- the tank lasted about 10% longer than here in CA on long distance trips (28 vs. 25 mpg)

- the indicated AFR on my wideband gage was about 0.8 to 1.0 points lower (richer)

- the calibration of my electronic (capacitive) fuel level sender was suddenly correct, after it had been way off for the last couple of years.

 

The first two items may have been influenced by the overall altitude (about 5000 ft average for the trip) that is probably not perfectly compensated in the ECU map. But I get the feeling that it has to do with the higher ethanol content and other crap they put in here. Does that sound reasonable or just coincidence?

[bsimon]

If I recall correctly, you have your ECU compensated for altitude with the internal atmospheric pressure sensor. I would guess you're seeing the results of unadulterated petrol. Can't explain the tank sender.

 

I noticed almost every gas pump in SD was labeled with "No Alcohol Content" in quite prominent lettering. Could be they're catering to the Harley crowd.

[powderbrake]

Ethanol has less energy per gallon, and always gives lower fuel mileage.

My Tahoe is a flex fuel model, and the manual states that with E85, you will get 25% worse gas mileage.

I notice the difference in 10% ethanol vs pure gasoline.

[rzempel]

I don't think WY and SD require the oxygenating additives that are required in CA. I suspect all of the symptoms you noticed are a direct result of that.

[slngsht]

agree with the others... it's the fuel, not the altitude.

[scannon]

The increase in gas mileage is due to lower pumping losses at higher altitudes. The throttle is open wider for a given speed which provides less restriction in the pumping process.

 

The internal combustion engine is just a big air compressor with a little fuel added to produce power.

[Kitcat]

I think you just kicked back, relaxed, and enjoyed the scenery and the throttle relaxed along with you:).

[turboeric]

I've certainly noticed differences, even among the same listed octane. My wife's Subaru runs perfectly happily on 87 octane here in B.C. (yes, we use the same rating system), but on Washington state 87 octane, it pings like mad. I also noticed in some places in Montana and Idaho, they were selling 85 octane as regular!

[MHKflyer52]

I don't think WY and SD require the oxygenating additives that are required in CA. I suspect all of the symptoms you noticed are a direct result of that.

 

agree with the others... it's the fuel, not the altitude.

 

I think you just kicked back, relaxed, and enjoyed the scenery and the throttle relaxed along with you:).

 

I've certainly noticed differences, even among the same listed octane. My wife's Subaru runs perfectly happily on 87 octane here in B.C. (yes, we use the same rating system), but on Washington state 87 octane, it pings like mad. I also noticed in some places in Montana and Idaho, they were selling 85 octane as regular!

 

Have to agree with the above folks that it is the fuel being real or better fuel and the fact that you where relaxed and not pushing the car as hard but enjoying the surroundings at least from the photos I have seen that have been posted so far.

By the way thanks for sharing your trip with us all that could not or did not take part in your adventure with your 7.

[slomove]

Looks like this is a good explanation.

 

I did some research in the meantime about the tank level sensor. Normal gasoline has a dielectric constant of 2.0, while ethanol has a whopping 24.3. That means adding 10% of ethanol roughly doubles the dielectric constant of the fuel mixture and a capacitive level sensor (if not compensated) might show twice the level.

 

I calibrated the sensor many years ago when the gas in CA probably did not have as much ethanol. For the last few years it always hit the peg when full and started reading only when fairly empty (I did not bother to recalibrate). Then, on the trip it showed only 3/4 when filled to the top. It all makes sense but does not give much confidence in the reading

[RossD]

I had a dead fuel gauge in a '53 CJ-3a (6 volt to 12 volt conversion done wrong). Since the tank was under the driver's seat, I could drive and shove a stick in the fuel tank while I was driving to check the level. A wet stick meant more driving! (I was 16 years old at the time, cut me a break!)

[danilo]

Along that line of thought My Lotus S2 had a painted stick (like one of those free wooden paint stir sticks but longer) as Supplied.. oem by Lotus with the Seven.

Undo tank cap... Insert stick .. Read fuel level contained.

Primitive as a stone axe.. But 100% accurate.

Make one and carry it as backup ?

[DeanG]

Along that line of thought My Lotus S2 had a painted stick (like one of those free wooden paint stir sticks but longer) as Supplied.. oem by Lotus with the Seven.

Undo tank cap... Insert stick .. Read fuel level contained.

Primitive as a stone axe.. But 100% accurate.

Make one and carry it as backup ?

 

Wow, I've never heard of such a thing. Could you please take some measurments and a few pictures. I would love to see it. I'm sure JD would give the pictures a place of honor on http://www.simplesevens.com

 

It seems odd but airliners still use the stick method for determining fuel load.

[slomove]

Along that line of thought My Lotus S2 had a painted stick (like one of those free wooden paint stir sticks but longer) as Supplied.. oem by Lotus with the Seven.

Undo tank cap... Insert stick .. Read fuel level contained.

Primitive as a stone axe.. But 100% accurate.

Make one and carry it as backup ?

 

That is indeed effective, cheap and lighter than a sender and gage

 

But the gage being off is not really an serious issue for me (as long as I know how much). I mentioned the surprising effect mainly out of scientific interest.