Excellent, another person proves that different fuel stations can show different MPG. Keep in mind, anyone else that tries this, that different cars will react differently. My 96 Tahoe showed these results with Shell vs other stations, but my 87 S15 gets the same MPG regardless of what goes in the tank. TBI fuel systems don't seem to care but port injection does.
Calculated the cost per mile using 2.50 per gallon for 87, 2.60 for 89 and 2.70 for 91 since this is the usual price spread, came up with the following. Used gallons times cost divided by miles travelled.
Based on this, it's cheapest to run the Shell 87 overall, and cheaper to run Shell 89 than the cheap 87, even though the best mileage came in with Shell 93. So if you are interested in saving gallons run the Shell 93, if you are interested in saving money run the Shell 87.
If you ever have to rebuild the engine, you might increase compression by an atmosphere or two to allow proper use of 93. I don't know what it would be on your engine, but on a Chevy 350 each atmosphere of compression with all else equal adds about 30HP and should increase efficiency by about 3 percent, but will require the high test.
you get some consistent gas mileage. It even starts to drop off evenly as the weather gets cooler. although maybe you don't live in a seasonal area.
Well, these numbers are averaged over thousands of miles. If you take a look at my gaslog you'll see it jumps around pretty good.
Yes, Virginia is seasonal. I'd say average temperatures have dropped maybe 20F across the period of the test. Do you think that's what we're seeing in the numbers?
I plan to loop around again (maybe several times) in the hopes consistent trends will emerge.
Originally Posted by VetteOwner
do your shell pumps have 10% ethonal in them too? cuz that 10% ethonal could be causing slightly less mpg cuz of the ethonal
I don't know. I've read that the ethanol mix is government mandated but it's like CAFE in that it's across all blends, and that Shell doesn't add it to the higher grades. I have no idea if that's true. It was one of my theories for the higher numbers on V-Power originally, though.
I've also been told that ethanol is involved with the Winter formula down here, and some places just don't bother to take the stickers off come warmer weather; again, I don't know for sure. I did see one sticker that said the gas "may contain up to 10% ethanol," which is just the sort of wording one might use for seasonal stuff.
I guess ethanol, ECU self-optimizing to consistent gas, lubricating additives... the actual reason wouldn't really matter (though it would be nice to know). If running on one particular brand is less expensive or gives one better mileage, that's the important bit.
Originally Posted by Telco
Excellent, another person proves that different fuel stations can show different MPG.
It's a little early to say this proves anything, I think. I need to get through the second "A" segment first to see if I return to baseline (or what the new baseline is). Then, what with changing temperatures, Winter gas, refined driving techniques, etc, loop through the whole test again (or a few times) to look for repeatable trends. Anything else could be explained away as noise.
Also, remember the original intent was to see if the V-Power detergent claim held up. It wasn't until I got into it that the consistent gas/higher-quality gas factor started being discussed. So I didn't really come into the test gathering all the information I maybe should have to test that.
As for cheapest gas per mile versus per gallon, if it looks like Shell gives me consistently better mileage I can do some data-gathering on that. With gas prices fluctuating as much as they do lately, I'd need to gather prices from both Shell and the cheapest generic stations I normally use at each fill. That'd get closer to a fair comparison than using fill costs alone. Example: Prices here are up about 10 cents a gallon right now from when I was in the middle of the Shell portion, so if I calculated based on fill prices, Shell would have an unfair advantage.
If you ever have to rebuild the engine...
I don't know whether to hope I never have to rebuild the engine, or that the car lasts me so well for so long I eventually need to.
Second "random regular" (10% Ethanol) segment complete; 34.05MPG over 391 miles. Refill was also stickered 10% Ethanol.
It's worth noting I was forced to make an aggressive, high-speed run during this segment. Before starting the run, efficiency for this tank was over 35MPG. If I had hypermiled the entire tank I would have managed at least 1MPG higher than the recorded figure.
Third "random regular" (10% Ethanol) segment complete; 33.86MPG over 376 miles. Refill was also stickered 10% Ethanol.
I don't think too much weight should be put on this tank's numbers. We had a lot of very foggy mornings which affected driving style (all the moisture in the air probably had a bearing, too). I also had to drive a bit more aggressively than normal overall, due to some schedule commitments. And my air dam came off near the end of the tank (not by choice; see, there was this parking curb...)