Better Gas Mileage using Shell Gas vs Chevron - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Not sure if the specifics of Shell vs Chevron have been addressed in these forums but I was using Chevron in my 98 Boxster only because of convenience, Chevron is on my route home from work. I filled my car up with Shell about a month ago over the weekend and didn't have to fill up for about 2 1/2 weeks of driving back and fourth to work. My commute is only 8 -10 miles one way, depending on traffic I take back roads when the freeway traffic is heavy. I filled up with Chevron on the next go around and my gas only lasted about 8 business days before I needed to fill up again. I kept the my Boxster parked on weekends to test my theory - now I need to zero out my travel mileage next time I fill up to confirm. Anyways - just wanted to share my experience as I am still a fairly new Boxster owner.

I have had that same experience with Murphy gas at WalMart vs Shell gas. Shell is all I get now unless I can't help it. When I can't, I get Chevron (oddly ). I never get no-name gas anymore like "Racetrack", "Kangaroo".

The base gasoline pretty much comes from the same refinery. Each brand then adds in the own additives. Stick with "Top Tier" gas and you should do fine. Also, stick with stations that have a high turn over. Gas gets old/bad, so going to a low turnover station increases the risk.

I use Wawa 92 unleaded. Plenty of turnover at any Wawa gas/convenience store...and I think they put a little bit of coffee in the gas for the extra boost. ha ha..

I understand that as various refiners push their product down the actual pipeline, it flows like cars on a frieght train, with no air gap. So the beginning and end of a large slug, where they might be a cross between two companies products, is sold on the open market at the gas terminal via the spot market. The independent stations are the primary customers of the spot market. So they may end up with buying a cross mix of two major refiners version of regular. That unknown is one reason why I stay away from the independant stations.

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I would think this situation happening depends on where you live. In Arizona we use to get all of our gasoline from one refinery in California but a few year back they built a pipeline from Texas. Not sure if it gets mixed but it certainly helped lower prices. Ethanol gets mixed into gas so there could be some variation on the percentage mix in the final product that could impact mileage as ethanol negatively affects mileage as it's less energy dense then gasoline. Again, stick to Top Tier gasoline and you should be fine.

When I fill the tank with Chevron my OBC reads 340 miles for the tank and when I fill with Shell it reads 299 miles for the tank. The reading is taken right after the fill sitting still. Any thoughts on what causes this?

I always use Shell. There is no ethanol in the premium grade.

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Did you check to make sure conditions are the same? Your current average mpg when filling the tank.

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Maybe in Canada, but there is ethanol in Shell premium in the US. I use only Sinclair locally, since it's the only non-ethanol gas in town (all grades).

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Yes conditions appear to be the same the fuel gauge needle is right on the full mark. For some reason the OBC is indicating I will get more miles on a tank of Chevron than a tank of Shell.

I get terrible gas mileage no matter what brand I put in... that's what makes these cars so much damn FUN

While I worked at both Shelby & Saleen during the EPA emissions certification process for new manufactured vehicles, 2 different emissions certification engineers were adamant about using nothing but Chevron Supreme in test cars. That's all I use & it's usually the most expensive option. I just paid $4.12 per gal at my local station.

MPG?? I'm more concerned about GPM( grins per mile). Nothing beats my Boxster S!!

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That might not be the most scientific test of MPG. Even if you were taking the exact mileage, the wind, how fast you drove and how often you hit red lights would effect it, but counting how many days a tank lasts is pretty unreliable.

was going to say is one station ethanol and one 100%?

I have been trying to manage the weight of my Boxster Spec race car through the amount of fuel on board. Spec racing has a minimum weight of 2650 lbs with driver at the end of the race. Usually, the top 3 finishers are weighed immediately following a race. Me and my car weighs about 2650lbs with no fuel, so I am trying to minimize the amount of fuel on board with the goal of having only 1 gallon left at the end of a race. Any additional fuel beyond the optimum amount is simply excess weight that is slowing me down. This should be simple, right? Thus far, this has been a massive failure due to the inaccuracies of the gas gauge. Not only is the gauge wrong, it is non-linear and not-repeatable, i.e., when the gas gauge shows a half tank, the number of gallons actually in the tank will vary. Thus, based on this experience, anything less than an almost absurd dedication to detail and exact measurements of fuel used, distance driven, and engine load will be useless in determining repeatable MPG numbers to the accuracy needed to compare one brand of gas to another.

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I'm pretty much in this camp. I seem to average around 24 mpg (pretty decent) no matter what the brand or conditions. I don't anylize it any deeper than that because I'm too busy enjoying the car!

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$4.12 per gallon! What's in that gas that it's $4.12 a gallon? The Chevron by my house is $2.83 for super.

To the original poster's question, though, one tankful is not near enough of a sample size to determine any changes in fuel economy. To accurately gauge fuel economy, you need a large sample size. For the argument about one brand of gas is better than another, I give you this.