[pmsteinm]

Because I am weird that way, I've added a tab to my auto maintenance spreadsheet for all fuel stops. I use the info from the car (ODO, "Data Since Refueling") and gas pump and keep track of things.

Something I've noticed is that I consistently add about .3 gallons more than the car says it has used. I know fuel volume changes with temperature but if that was the cause I would expect some fill-ups to take more and some less than the car says. I played with the car numbers assuming worse case rounding errors but it still doesn't account for the difference.

When I fill up I don't top off. When the pump clicks off I don't try to add more.

[Autoregression]

Originally Posted by pmsteinm

Something I've noticed is that I consistently add about .3 gallons more than the car says it has used.

Possibilities:
1. Car is inaccurate, and assumes a specific volume of fuel after completion of fillup.
2. Pump is inaccurate and is ripping you off.

Probably #1, as pumps get audited and you have probably filled up at more than one station/pump.

A funny quirk of one of my old cars (Audi RS4) is that the trip computer used Audi A4 constants, yet the RS4 had a slightly different shaped tank (more volume above the "full" sensor). It meant a few "free miles" on the distance remaining calculation until the fuel level got below the sensor.

Perhaps the M5 uses some 5-series assumptions? It would be interesting to know if those cars also have an inaccuracy.

[MackSea70]

Originally Posted by pmsteinm

Because I am weird that way, I've added a tab to my auto maintenance spreadsheet for all fuel stops. I use the info from the car (ODO, "Data Since Refueling") and gas pump and keep track of things.

Something I've noticed is that I consistently add about .3 gallons more than the car says it has used. I know fuel volume changes with temperature but if that was the cause I would expect some fill-ups to take more and some less than the car says. I played with the car numbers assuming worse case rounding errors but it still doesn't account for the difference.

When I fill up I don't top off. When the pump clicks off I don't try to add more.

You need to stop doing this.

You’re going to ruin all the fun for the rest of us when you conclude the car gets 8mpg.

Might I suggest a round of golf and a long stay at the 19th hole. That should give you plenty for your mind to mull over.

[pbonsalb]

I don’t even know where “data since refueling” is located, but I probably fill up my 1 gallon water/meth tank every 2 tanks of gas on average so maybe my consumption is even further off.

[mavz]

Originally Posted by MackSea70

You need to stop doing this.

You’re going to ruin all the fun for the rest of us when you conclude the car gets 8mpg.

Might I suggest a round of golf and a long stay at the 19th hole. That should give you plenty for your mind to mull over.

I do what he does too similarly, been doing it years (just because). The way I drive, I can say I'm getting more than 8mpg tho

[pmsteinm]

Originally Posted by MackSea70

You need to stop doing this.

You’re going to ruin all the fun for the rest of us when you conclude the car gets 8mpg.

Might I suggest a round of golf and a long stay at the 19th hole. That should give you plenty for your mind to mull over.

Ha! I also get annoyed when my paystub doesn't quite match my spreadsheet.

I don't see how the car can be wrong. I assume the amount of fuel is based on how much its metering in with DI. That should be pretty close to perfect or the engine wouldn't run correctly.

I have been using the same gas station and pump actually, since I'm on the Top Teir kick for now. I went through that with my previous cars, but usually quit worrying about it after the "newness" wore off.

[Aronis]

oh my.

Mike

[micvite]

Well... if we're assuming that the HPFP is what's counting how much gas goes through, you're always going to have stuff left over in the lines that the pump has already yoinked out of the tank into the lines but hasn't counted yet hence why you're filling up more than the car thinks it's used. That being said every pump also has different click offs.

[pbonsalb]

Maybe a neighbor is stealing gas at night?

[pmsteinm]

I figured it was measuring based on injector activation and since it has stored calibrations for each one it would know how much fuel is being injected. But maybe that is too high precision to be worth the math so they count or measure somewhere else (like the fuel pump).

I feel like I have a hybrid compared to the V. It makes sense that with 2/3 the displacement I get better mileage when not pushing, and when pushing it drops to about the same. And with the larger tank I can finally just get gas once a week instead of every 4 days. I try to fill up at 1/4 tank just in case the BMW urban legend about fuel pump failures due to temperature applies.