Hopefully someone can explain this phenomenon

My truck is really confusing me right now, I topped off the rear tank with b5 biodiesel blend before taking a lil over 30 mile trip to my sis house and then topped off both tanks and the back tank wouldn't even take a full gallon so I did some research and it seems that biodiesel yields better mileage so after I put bout 80 miles on the front tank I topped it off with b20 figuring that with a 20 gal tank it'd work out close to b5 it took bout 4.5 gal and I drove bout 240 miles on it before last night when it started acting like it was bout to run empty I bled some air from the valve on the fuel filter and it stopped for a bit but then started doing it again so I switched over to the back tank and bled again and it hasn't done it on the back tank wich puts me in the mind that the front may be nearly empty but that doesn't make sense even with the mileage I was getting before then I kicked around the idea that the fuel filter might need changed since I'd read that when you first switch to biodiesel you'll need to replace it soon as the biodiesel cleans out the system but that dissent make sense to me because if it was the filter then I'd have the same problem on the back tank too right? I intend to try to fill it later to see how much fuel is left (fuel gauge doesn't work probably should've mentioned that sooner, sorry) but I'm unsure I'll have enough $ to fill it, I hope so lol anyways please help if you can

I think you may have a tank selector valve going bad. Migth have the rear tanks selected but be pulling from the front tank.

I'm sorry but that doesn't seem to make any sense I was having issues with the front tank selected and when switched to the back tank it cleared up if I'm missing something please elaborate

Thats what I was thinking too. The tank selecter valves can be taken apart but you need to read up on what needs to be done to get the valve apart first. They don't have screws or bolts holding them together...

Again how would the tank selector valve cause this issue(I've utilized both tanks many times and know that previously it was working fine and I'm almost certain it still is as when I had it on the back tank it did use fuel from the back tank and when the issue I was having while running the front track was fixed by switching to the back tank

I ran B99 once and it promptly plugged my filter up with a gelatinous sludge from the 25 year old fuel system...

FYI - I never run more than 200 miles on a tank of fuel, 240 is really pushing it for tank capacity.

And I have never got better econonomy on BioD than on regular D...

I dunno how bout the fuel sock on the p/u in the tank? could it be clogged? just thinking out loud it would explain the sudden change wouldn't it guys?

Had a selector valve fail on a customers truck that did the same exact thing. Drawing from the front and returning to the rear tank.

What was found that the pickup screen assembly on the front tank had degraded and was in pieces on the bottom of the tank and a piece of the pickup had also made its way into the selector valve causing it to partially hang up and doing exactly what has been described.

As Gary said, the valve assemblies can be taken apart but are riveted together. Simple machine screws and nylon stop nuts can be used upon cleaning and reassembly.

SparkandFire said:

I ran B99 once and it promptly plugged my filter up with a gelatinous sludge from the 25 year old fuel system...

FYI - I never run more than 200 miles on a tank of fuel, 240 is really pushing it for tank capacity.

And I have never got better econonomy on BioD than on regular D...

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I get nearly 300 miles on my front tank. I know this because the sender isn't working and must estimate mileage so I don't choke off on the freeway. I switch to rear tank at 290 miles on the trip.

I typically refuel both tanks when the trip reads 430-445 miles, but I'm not stone cold empty either. I also top off to the neck for reference.

I had a selector switch fail on an 83 F-150..... that truck did not have a return, but it stuck halfway between the tanks, to were the path to both tanks were open, I was running off the back tank, and the front tank would siphon off gas as it was running. I was headed to town, and it ran out.... so I walked to a phone to call dad, we got a can of gas, and put some in the back tank and drove to a station and added gas to the rear tank. A few days later, dad was driving the truck, and he wondered if there was any gas in the front tank, when I was out in the back tank. I knew the front tank was empty, because I switched tanks when it began to stall on the front tank. When he switched it, there was almost a quarter tank in the front. So, when I was sitting on the side of the road out of gas, there was actually gas in the empty front tank.......

SparkandFire said:

I ran B99 once and it promptly plugged my filter up with a gelatinous sludge from the 25 year old fuel system...

FYI - I never run more than 200 miles on a tank of fuel, 240 is really pushing it for tank capacity.

And I have never got better econonomy on BioD than on regular D...

Click to expand...

man ive ran over 340 miles on my front tank

I always switch at 1/4 tank

Usually get around 200 miles to a tank

when I refill its about 11gal to top them off

Likewise, I also switch tanks and refill when at 1/4 tank, why press my luck. Truck runs just as good on the top half of the tank as the bottom, and overall it's the miles you drive that determines the fuel use, not the amount you squeeze out of a tank.

93cc7.3 said:

man ive ran over 340 miles on my front tank

Click to expand...

Methinks i may have lost my showerheads...

BUT the gauge is always at empty around about 250 miles give or take... Any more than that and I start to sputter out.

93cc7.3 I'm usually not into it if it ain't 4x4 but that truck looks sweet with those stacks! Thanks for all the input everyone I was on a 850 mile haul and my damn phone charger went out so I count keep up but I came to a few realizations 1 currently I seem to be getting better fuel mileage the shorter the distance between fills (puzzling as if the bottom of the tank is different than the top) 2 I used to go 200 miles then top off and it take just over 10 gal (i changed the fuel filter on the trip it was getting clogged from the cleaning the bio had done, it helped a bit but I then also realized that being so preoccupied with my kids and many other things I'd neglected to clean my k&n in the last say 20k miles of hard driving/mudding/hauling yes I know dip stick move (cleaning it tomorrow) and 3 I'm burning oil much faster than before running the bio so I font know if that's because it cleaned things out and now more gets through or what but I gotta figure something out I went through over 2 gallons on that trip alone