Now this was weird

[Bill]

This last weekend I went to Glade Park, Colorado to visit my brother who lives up on the Mesa above the monument. I was watching my milage just to see what it was doing to try to determine wether I should trade trucks or not as the last trip out to see Donnie I didn't do so good. That trip I was getting about 15.5 and sometimes 16.5 but the overall average was closer to the 15.5. On the trip out I too the interstate west of Denver and my overall average was 14.4. Kind of torked me and I was just about ready to trade like YESTERDAY.
Well when I wen't to leave his place I stopped and bought gas. Something weird happened. The had the 92 octane on the left rather than the right side and I didn't read it just punched in the card and hit the botton and started cleaning the windshield.
Well I went to check and the light above the 92 was blinking while it was filling telling me I had put in the 92 by mistake. I thought what the heck, its almost full might as well finish filling it. Well we took off from Grand Junction and I reset the computer to see what was happening with the milage with the 92 octain in it. From Grand Junction to Rifle and driving 75 I got 20.1 miles per gallon. From there on home it dropped down to 19.0 miles per gallon and stayed there. Now thats a heck of a jump up and well worth the 10 cents per gallon differance with 4.6 mpg more and almost a 30% increase. But what kills me is most of the vehicles I have ever driven did just about as well with the lower as it did with the higher octane.
So why that big a differance.

[Jack]

Headwind? tailwind? maybe

[klsm54]

Back in the old days, you remember Bill, when gas had lead in it. Regular was about $0.30 a gallon and Hi-test was about $0.34 a gallon. I always checked my mileage, for 3 or 4 tanks in a row, with regular and hi-test. Found some cars were well worth the extra $0.04 per gallon, on others there was little, or no, difference.

After gas got more expensive ..... or maybe I got cheaper ..... I quit trying hi-test any more. But I guess when you look at it as a percentage thing, it would still be worth checking it out.

[jabba]

Elevation?

The higher octane gas actually burns slower than the lower octane.

It's mostly to control knock. But I have seen it yield gas mileage too.

Jabba

[Bill]

Jabba, for the last 2/3 of the trip I was pushing into the wind and for about the fist third I had a side wind. Some of those winds were pretty strong at times. Still nothing I can think of can account for that much increas in MPG. And I monitored the MPG computer constantly as I thought maybe something was amiss but then I thought that something really was on the way out because I got great milage going over the passes and lousey milage on the flats. Nothing was consistant going out but on the way back everything looked normal. Plus the Expy run like a top. But I kept wondering if something changed in the timing or something causing all this.

[dakota]

I think your vehicle has a computer that retards the spark on lower octane gas, so it will not knock. The retarding will cause lower power and cause more gas to burn.

[jabba]

Oh yeah. New cars and spark sensors.

Nice pick up Dakota.

I forgot about dem.

Jabba

[Bill]

So what your saying is this. Me burning Unleded plus was making the truck retard the spark and made the truck under powered. Yup your right on that one. It was a bit underpowered but there were times I was averageing 17 to 18 mpg. Very seldom running over 65 though. Although I have done that well running between 70 and 75 before but not often. I have never gotten the 20.1 mpg though since I owned it and that was with a crosswind and about 5-6,000 in altitude. The 19 mpg was with a 20 mph head wind and from 6,000 to 10,000 ft in altitude. I'm going to see what it gets driving back and forth to work as I was getting 12.5 MPG doing that.

[jimiowa]

I think at the higher altitude the higher octane will do much better.
I know years ago I had a 84 Chrysler New Yorker with the Turbo Charged 4 cyl. Here in the flatlands it ran great on 90 octane ethanol.
I went out to Southern Colorado and forgot to fuel up in Colorado Springs. I pulled into a gas station around Canyon City and all they had was 83 octane, the darn think hic upped-and spark knocked under a pull on hills till I found some octane booster to add to that tank.
So I can see that the higher octane fuel is a benifit at higher altitudes.
Another note there are no Texaco stations in Iowa anymore but in states where they are I find I always get better milage on their fuel.

BTW Bill if you were on the Grande Mesa did you happen to go through Cedar Edge where my little brother lives?

[jabba]

Actually, higher octane is LESS important at higher elevations. That's why they don't sell high octane fuel there. Because of the elevation, the air is thinner, and therefore the compression ration is less, therefore lowering the likelihood of premature detonation (spark knock).

Jabba

[Bill]

I don't know what the heck the higher octaine does but I can sure tell it on the MPG computer. Even driving back and forth to work is about 8% better. I keep resetting the MPG computer to see what differance it makes for differant types of driving. Found out that going up the hill to go to work I get 6.4 mpg but when averaged out I get 13.4 runing back and forth to work. That was taken over a 2 day average and its still climbing. I use to average 12.4 MAX.

Jim, I didn't get up on the Grand Mesa I don't think. I went south thur the park (only way to get up to the brothers without diving 100 miles around. He lives at Glade Park.

[deputydon]

Bill I've been there years ago.... Beauiful country I can see why Bobby loves it.

[klsm54]

Ah....so Bill...you're talking about figures from the mileage computer, not actual mileage calculated when you fill up?

I never trust a mileage test unless it is done over several tanks of gas. Just too many factors that can influence the "True" milage.

I'd like to see a test done over 3 or 4 tanks of gas and see what the actual mileage was.... versus what the mileage computer said it was.

[Bill]

I was keeping track of it on the trip meter and the pumps and matching it to the trip meter and it was comming out pretty close or close enough I didn't argue with the results. Actually it came out higher by going by the gallons and miles by about .5 mpg but I go buy the computer. That average was with 2 fillups so I figured it was going to be pretty close.