I followed the advice of a thread here that said you can squeeze up to 4 additional gallons beyond tank capacity. On Monday morning I filled up and fit in 38 gallons total, it took forever, but not seeing the needle move off of full until around 120 commute miles had been driven was a beautiful site.

I always trusted my O/H even though many on here complained about it's inaccuracies, I had occasionally checked it by crunching the numbers in my head, rounding off where needed. It always seemed close enough to not worry about it, well today I got the itchin' to top off after driving 206 commute miles (I wanted the needle pegged again). I topped off to the same level as last time about 1" below the vent hole in the fill neck, it took 12.94 gallons.

My O/H had been reading 14.4mpg lately, Using my handy dandy solar powered calculator, I went to work to decipher the long anticipated question, "Is my O/H accurate or not?"

This is commute traffic ie. 23 miles in 45 minutes includes climbing a 700ft pass in about 1 mile.

206/12.94 = 15.91mpg, 1.5 miles off in my favor.

This is with out Howes Meaner Kleaner, since they won't return my emails. I found Power Service locally last night and dumped it in with this fill-up, I hope the 8% increase is accurate. 17.1mpg would be beautiful.

17.1mpg would equal my 5.0 Mustang in commute traffic.

 

I must be doing something wrong. I run mine to below the red "E" and the most I am able to jam in the tank is about 36 gallons. Never been able to put in the 38-40 that some can. However, I do like seeing the needle on the full mark at 200-220 miles. If my gas gauge were linear, I would be getting 1000 miles to a tank.

 

Patience is all I can think of when you're topping off, do you fill it until you can see the fuel level in the neck is just below the vent hole or just until you start seeing foam? Once I see foam I think it's still about 1-2 gallons to go, you have to wait for the foam to back down the neck before you pump.

My first time was last Monday, I had 44 miles on the O/H and I was able to put in 34.7 gallons...I calculated that I had about 3 gallons in there to start off.

 

I fill it up to the top of the filler tube and give the truck a shake. I've gone to the point where the needle on the fuel gauge is almost touching the peg to left of the "E" and way past "0" DTE.

 

Weird? I know the first time I did it, the pump clicked off as full and I was able to put in almost another $10.00.

I filled my wife's 02 gasser (26gal) last night and after it clicked off I was able to get in an extra 1.9gal before it started pouring rain and I gave up. I don't know how much she had left in it to start though.

 

I've got the fuel tank vent mod and I regularly fill up with 31-32gal each and every fill up. I fill up when the DTE reads 0 or close to it!! Prior to the vent mod I would regularly fill up with 28-29gal. This leads me to believe that my fuel gauge reads low and that I could go much further on a tank if needed. I'd rather have it that way than the other!!