FK 12 Gal Aux Fuel Tank DIY Install

[MAC25LC]

Just as my main tank hit 3/4 full, fuel transferred quickly from the 12gal aux tank to full on OEM tank, my Miles to Empty, went back up to what it was when I last filled. So far so good.

Okay, question, it did the same for the 2nd time, filled up at 3/4 full, now if you do the the math, each quarter tank of gas should be 4.47 gallons on 17.9 gal tank. Or am I doing the math wrong on the main and aux tank?
Just went the 3rd time to 3/4 full, no gas transfer.
If above math is correct, 4.47, it should have only transferred x2 8.95 gal, so there still should be 3.05 gal left in the Aux 12 gal tank.
Would it be normal for 3 gal left, or will it eventually fill the main tank.
Has anyone else noticed when the aux tank fills main tank and when, how many times?

 

[Swerdna]

Okay, question, it did the same for the 2nd time, filled up at 3/4 full, now if you do the the math, each quarter tank of gas should be 4.47 gallons on 17.9 gal tank. Or am I doing the math wrong on the main and aux tank?
Just went the 3rd time to 3/4 full, no gas transfer.
If above math is correct, 4.47, it should have only transferred x2 8.95 gal, so there still should be 3.05 gal left in the Aux 12 gal tank.
Would it be normal for 3 gal left, or will it eventually fill the main tank.
Has anyone else noticed when the aux tank fills main tank and when, how many times?

I am to ADD to be able to catch it every time but I’m confident it’s getting almost all of those 11+ gallons in the aux as I’ve gotten over 500 miles between fill ups.

What I’m curious about is my wife took the truck for the week. What happens if she doesn’t fill the tank(s) at the pump? Some of the gas will go in each tank I assume. It will be an interesting experiment.

 

[MAC25LC]

Just a heads up, if you are planning on running wiring to the front from battery, I suggest you do it before you install the 12 gal tank. You. can still do it, but it’s more of a pain in the arse.

 

[MAC25LC]

Did a 2nd fill up from 1/2 tank, again the aux tank filled the main tank twice, each time at 3/4 full line, didn’t see or show any more siphoning from aux tank. I will be at around 470-475 mile, now if I ran it empty, should be at 494, only getting 16.6 mpg.
So I take it, that the first quarter tank, is around 6 gal.
Has anyone else watched it closely to see when and how many times it fills main tank?
Thanks

 

[MAC25LC]

Just did fill up, said I had 9 MTE, put in 27.819 gallons. With both tanks totally empty should be right around 17.9+12=29.9
My gauge said I was getting 16.6, but when I take miles on the tank 478 and divide by gallons put in 27.819, comes to 17.18.

So far very happy having the extra 12 gallons and to me it was worth the investment.

 

[MAC25LC]

3rd fill up and the same on aux tank filling main tank, soon as I get to the 3/4 full line, it fills it twice

 

[MAC25LC]

Now this is getting weird, my last 2 fill-ups—aux tank filled main tank at 3/4 full, then when it was at around half tank it filled it to just past 3/4.
So first few fill-ups aux tank filled the main tank at 3/4 full to full tank.
Anyone else’s aux tank doing this?

 

[Swerdna]

I stopped paying real attention (a bit ADD) and the last “top off” seems a little less consistent as to when it hits. I’ve driven a good 10k and have had no issues. All but one or two fill ups have been with less than 30 miles to empty and taken 25-27 gallons. Our road trips I’ve been seeing over 600 miles on a single fillup.