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The donkey CRX · 06-26-2015, 06:53 PM

OG, most of what I am going to say is also what I "BELIEVE" or "THINK" is happening with this subject. So take it all with a grain of salt.

In the past year I have been constantly trying new driving techniques or testing new modifications to our cars. In order to get the fastest feedback on any change I "THINK" I need at least a 300 mile test and as much as possible around the same outside temps and wind conditions. This would be 3 round trip commutes for me. I have "found" that it is hard to get even 3 trips to all be close to the same and not have one be the outlier (rain, headwind in both directions, cold front, construction delays etc.) But some time I can feel like that all three trips are close and I can trust the results. If I fill up after 5 or 6 trips, I always have at least 2 of those trips that are way subpar as far as MPGs. So my experience is that the more miles you travel between fill ups, the more likely you will have a lower total MPG. But I also "think" over a 6 month or year time frame, all this washes out when you compare 90 day and same time last year numbers. Of course, this assumes all of your fill ups are as consistent as possible. All my fill ups are at the same pump with the car in the exact same spot, one click, and at about the same time of day.

Here are some other things I "think" I know:

When I did my alt delete, there was a discussion that not running at 13 or 14 volts at all times might effect the output or pressure of the fuel pump on our cars. I added a high quality digital fuel pressure gauge to monitor how the fuel pump reacted to changes in volts. What I found is that a voltage change had no effect on fuel pressure and the pressure only fluctuated based on throttle position. I saw no difference between the fuel pressure when the tank was full or if it was almost empty. But I can only say that about this one car. I am convinced enough that this is a non issue, I don't think I will install a fuel pressure gauge on any of our other cars.

So, to sum up this long and maybe useless post, I have never seen any evidence that causes me to"believe" that the amount of gas in the tank has anything to do with your long range MPG.

Thanks

06-26-2015, 06:53 PM	#42 (permalink)
The donkey CRX Master EcoModder Join Date: Feb 2013 Location: TN Posts: 300 MULE VX - '92 Honda civic VX Team Honda 90 day: 92.6 mpg (US) White 94 VX "Show Car" - '94 Honda Civic VX VX 90 day: 79.92 mpg (US) The Walrus - '02 Honda Insight base Gen-1 Insights 90 day: 100.88 mpg (US) Thanks: 399 Thanked 564 Times in 189 Posts	reply to OGVX OG, most of what I am going to say is also what I "BELIEVE" or "THINK" is happening with this subject. So take it all with a grain of salt. In the past year I have been constantly trying new driving techniques or testing new modifications to our cars. In order to get the fastest feedback on any change I "THINK" I need at least a 300 mile test and as much as possible around the same outside temps and wind conditions. This would be 3 round trip commutes for me. I have "found" that it is hard to get even 3 trips to all be close to the same and not have one be the outlier (rain, headwind in both directions, cold front, construction delays etc.) But some time I can feel like that all three trips are close and I can trust the results. If I fill up after 5 or 6 trips, I always have at least 2 of those trips that are way subpar as far as MPGs. So my experience is that the more miles you travel between fill ups, the more likely you will have a lower total MPG. But I also "think" over a 6 month or year time frame, all this washes out when you compare 90 day and same time last year numbers. Of course, this assumes all of your fill ups are as consistent as possible. All my fill ups are at the same pump with the car in the exact same spot, one click, and at about the same time of day. Here are some other things I "think" I know: When I did my alt delete, there was a discussion that not running at 13 or 14 volts at all times might effect the output or pressure of the fuel pump on our cars. I added a high quality digital fuel pressure gauge to monitor how the fuel pump reacted to changes in volts. What I found is that a voltage change had no effect on fuel pressure and the pressure only fluctuated based on throttle position. I saw no difference between the fuel pressure when the tank was full or if it was almost empty. But I can only say that about this one car. I am convinced enough that this is a non issue, I don't think I will install a fuel pressure gauge on any of our other cars. So, to sum up this long and maybe useless post, I have never seen any evidence that causes me to"believe" that the amount of gas in the tank has anything to do with your long range MPG. Thanks