fuel question
 

shell mobil sunoco hess what do you use, I noticed better results with mobil over shell, this tank is sunoco

All fuels are basically refined to the same standards.Their upper and lower heating values will be identical.One brand over another should not make any difference.That's not what oil companies would have you believe,however that's the reality of it.A laboratory is the best places to test such things, as there are so many variables which can cause a change in mpg in the real world,you would be hard-pressed to sort it all out.

I did use BP all of the time until one of the Texaco stations started being $.10-$.15 a gallon cheaper. I switched and started using Texaco most of the time and saw my FE go up on my '88 Escort. I doesn't seem to matter to the '97 Escort it gets about the same mileage on either. I think the major differences in brands is the additives they put into their fuel.

I've put BP in my tank the past two fillups. My FE went up, but that's probably due to my driving habits and tire pressure more than anything. Besides, it would probably take more than a couple tanks to come to any sort of reasonable conclusion.

Pump calibrations.
 

Always remember that gas station pumps are rarely spot on accurate. All jurisdictions allow some percentage error in measurement. Some allow as much as +/- 5%.

Let's say you start with a full tank and drive 300 miles. When you fill up the pump registered 10 gallons. However, that pump reads 2.5% low so you really put 10.25 gallons (the real amount you burned) in your tank. You figure your FE based on the pump readout and figure you got 30 mpg.

You then drive back to your starting point and fill up again. But, this pump reads 2.5% high. You put 10.25 gallons (the real amount you burned) into your tank but the pump readout is 10.4 gallons. You figure your mileage based on the pump readout and figure you got only 28.85 mpg.

If the first pump is Texaco and the second pump is Mobil, you arrive at the erroneous conclusion that you get better mileage burning Texaco when in reality you got exactly the same mileage from both.

But can that not be somewhat controlled by filling up at the same pump, same time, same direction, etc.? I mean, even if that isn't possible, sticking with the same brand over several tanks should increase the odds of the percent error of the pump measurements balancing out over time. Makes sense in my little mind. :p

I usually use the same pump at the same station, but I have also used different pumps at different stations with the same results and I always fill to the cap.

Correct ptsmith24.
 

You are correct. Filling up with different pumps will average out over time. The original poster was talking about filling up with two different brands and noting a mileage difference and I was pointing out that the difference could be entirely due to errors in measurement.

Another point. Supposed he filled up with Brand X and drove 300 miles on a calm day. Then filled up with Brand Y and drove 300 miles but it was into a 15 mph headwind. Without allowing for the wind, it would appear that Brand X gives better mileage than Brand Y.

Now, if you keep very careful records about which fuel (and pump) you use on every fillup, record the weather and road conditions, etc. You really can't conclude that one brand of go-juice is really any better than another.

I only use Shell, Mobil or Chevron/Texaco. All 3 of those have top tier additives, may or may not help with FE, but I enjoy the peace of mind knowing at least it will help prevent some gunk build up.

Do you have any actual proof of this (besides commercials) somewhere or what? I really am curious...