Correct way to check MPG on VX

[Coconut Sunrise]

ok i know the basics of MPG.....However to top off a VX takes some skill
doing at the pump is not the way since all fuel pumps not the same
some I can trickle the fuel and some I cannot. the only way I get a true Top off on level ground is with small funnel and a a graduated cylinder. which is a pain when you are doing a full tank.
The vx fuel tank Neck holds some fuel and unless you shake car to get air pockets
out your MPG will vary.

when I use the same pump and same fuel stop I get numbers all over the place driving the same daily route,

so just what tactics do you guys to get your numbers

coconut

[theholycow]

There's no reasonable way to get the kind of single-tank accuracy you're looking for. The best you can do is go to the same pump, facing the same direction, at the same time of day, and stop pumping when it clicks off the first time. This is pretty easy if you have a standard driving routine/commute, maybe not so easy if you don't. It's not good enough to say with a single tank if something is working; you can't depend on any better consistency from traffic, weather, and random other conditions anyway. Topping off, trickling, and shaking out air pockets is only going to make it worse.

Try to be as consistent as possible, but what's most important is keeping a log and seeing a graph over time.

[Jay2TheRescue]

I agree. I try to go to the same station, pump, and face the same direction. I put the pump on high, and stop when it clicks off, and don't top off. If you're consistent with your procedures, you will be as accurate as possible.

[Coconut Sunrise]

well I have done that also, However sometime after the pump clicks off i can put in a gallon more or 1.75 gallon more to top it off. So my pump does not always click of at same level by these observations.

[Jay2TheRescue]

I never top off. The whole procedure of topping off is so imprecise. I pump till it clicks off, and I'm done.

[theholycow]

Originally Posted by Coconut Sunrise

well I have done that also, However sometime after the pump clicks off i can put in a gallon more or 1.75 gallon more to top it off. So my pump does not always click of at same level by these observations.

Yup, that's how it is. I would attribute that more to the extremely inconsistent nature of topping off than to the moderately inconsistent nature of stopping at the first click.

[trollbait]

Maybe not a concern with a VX, but newer cars have evaporative controls on the gas tank. Topping off could damage them.

[Coconut Sunrise]

Anyone ever knocked out the top of the fuel filler restriction ? Unleaded is all we have so its not needed and topping off would be easier. I see no issue with doing this. Get one from the junk yard and adapt it. My TDI wagon has a Vent relief valve that allows topping off.

[bobc455]

Multi-tank averages.

I remember seeing some kind of "real world horsepower" test several years ago in one of the magazines, where the cars got some insane MPG numbers (I think 31 MPG for a 454 Camaro with huge cam, 1050CFM carb, etc.). But when I read the article, the "real world test loop" was maybe 25 miles and they didn't fill up at the same gas station each time. So in reality, they calculated that this Camaro used slightly less than a gallon on the test loop... Anyone think that is accurate? NOT

When I had a spreadsheet going for my car, I had a column with the MPG per tank, and another column with a 10-tank running average. After running that for a while, I think a 3- to 5-tank running average is most useful (especially since I would "tweak" more than once every 10 tankfuls).

-Bob C.

[Jay2TheRescue]

Originally Posted by Coconut Sunrise

Anyone ever knocked out the top of the fuel filler restriction ? Unleaded is all we have so its not needed and topping off would be easier. I see no issue with doing this. Get one from the junk yard and adapt it. My TDI wagon has a Vent relief valve that allows topping off.

Depends on what state you're in. Here in Virginia, the restrictor is checked for both safety and emissions inspections. If its removed or tampered with, your vehicle will fail, and you will be unable to legally register and operate it on public roads.