LVTony

Here's a fun one.

I replaced my OEM tank with an Aerotank 75 gallon tank set. There's the main tank (where the OEM tank was located) and a small ~15 gallon "donut" tank that sits between the bottom of the bed and the spare tire. The cable for the spare tire actually threads through the "donut".

This small tank is attached to the large tank via four lines, so when I park in the driveway, some fuel will drain back to the donut tank. The sender doesn't read off full until ~460 miles in the city unless I park in the driveway. It takes a couple minutes for the small tank to drain back into the large tank.

For those few minutes, my DTE will go from low 400s to almost 600 when the fuel has drained back and the sender is back on full again.

This is a great tank. If you need to tow and/or go long distance, this is one to keep in mind. I still have all my bedspace. I try to fill up a little under 3/8s of a tank left. It's right about 60 gallons then.

DiEseLjunKy

With regards to doing hand calcs.

If the digital overhead is not right and you're basing your hand calc on what a digital speedometer says your mileage was how can you be so trusting of one digital gauge on the one hand and yet mistrust the other as wrong?

Also if you are not filling up at the same exact pump parked in the same spot every time you cannot be certain you are getting the same amount of fuel in there every time. The capacity of these tanks is 34 gal but they are slightly bigger than that to allow for fuel expansion. Imagine if your truck was parked pulling up a 45 degree incline and you try to put fuel in the empty tank like that. Well obviously you won't be able to get more than half a tank before it "fills up" (depending on where the filler neck hose hooks into the tank, i'd have to look at that to be certain). By the same token a slight gradiant variance of one or two inches at different gas station pumps will make your truck "fill up" sooner or later with a +/- quarter gallon or so of fuel than it would at your usual regular fuel stop. It may not be much difference but it won't take a lot to make your hand calc mpg be off.

The bottom line of what I'm saying is - if you don't know you are putting the EXACT same amount of fuel in there every time your hand calc is always going to be wrong. If you're not fueling at the exact same pump parked in the same manner every time your numbers will be off slightly.

One more note on digital speedometer readings - my class 8 Volvo has a digital odometer in the dashboard. It also has a hubodometer out on one of the rear drive axles. When the truck was brand new it had 430 miles on the digital in the dash after being driven down from the assembly plant and delivered to the dealer where they installed a new hubodometer that read 0 miles. Now at almost 200K miles the variance is about 3K miles instead of the 430 it should be. So which one should I trust? Just something to think about.

Believe what you want and do as you please. But personally with this in mind, right or wrong, I think I'll trust the overhead in my Ram knows what mpg's I'm getting better than imprecise hand calcs.

JohnInNH

Let's see.... Mile markers and your ODOMETER check em. then do some math and keep track of your fuel usage. I have a log book.

My overhead is off 1.5 to 2.5 miles per gallon.

I fill up and burp the tank.. I fill to the top of the neck. Takes about 15 minutes! (I need to do the vent mod)