Just start using long unsued fuel tank?

Cubey

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On my F250, I never really needed to use the rear tank, I could go pretty far even at 13mpg before needing to refuel. I always thought about it but never did.

It's a bit worse in the RV at about 9.2 hwy MPG. It calculates as ~8 sometimes and ~10 at others. My average this month so far, including a small amount of city driving, is 8.9mpg. (I wish I could find a free C6 overdrive and 3.55 rear end for double digits, ha!)

Sadly, fuel prices are going up suddenly. Diesel has jumped 10-15 cents since 4 days ago. I think I need to start using my rear tank to save on fuel costs. But, who knows when it was last used. There's no telling how nasty it is.

Would something like Power Service Clear-Diesel be adequate to dump in the tank before I fill it up? They say.... "The Fuel Polishing Formula of Clear-Diesel Fuel & Tank Cleaner removes water and slime, disperses contaminants and stabilizes fuel during long-term storage."

Or am I asking for trouble by suddenly using it without dropping it and properly cleaning it? I get that I might need to change my fuel filter soon after, but for ~$25 (cleaner+filter) I would have my rear tank to use. It would take a long while to recover the $25 cost, but still. The longer I put it off, the worse it's going to be.

My selector valve seems to be working, or it clicks at least, so there's a chance it's fine. What typically kills them, excessive use? If so, I doubt it's been used much, being so low miles.
 
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u2slow

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How long has it been in there? I have run sketchy fuel before, and so-far so-good with 2 stage filtering on my truck. It doesn't go stale per se, but it grows things when there's moisture.

I'd most likely top it off with fuel and a std dose of additive.... and run it.

If you're nervous, don't try running it with the other tank empty, and keep a spare filter on-hand just in case.
 

Shadetreemechanic

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You are overthinking it. If the cap has been on the tank, just turn it on and see what happens.
Do carry a spare filter, and if you are really worried, plumb a cheap clear disposible prefilter in the hose ahead of the lift pump. That way if you do have issues you can quickly see what they are.
 

Cubey

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How long has it been in there?

There's no telling. It could be 2 years or it could be 20 years.

With the rear tank selected (engine off), the gauge shows a bit under half a tank. Presumably it's a 22 gallon rear tank, as that's what replacements are for 85 E350s. If I had to guess, I'd say it has 8-9 gallons of highly questionable fuel in the rear tank.

After I switch from front to rear then back to front again with the engine off, the engine kind of hiccups for a second when I start it, as if it had a bit of air in the line. I guess some fuel in the line from the lift pump drains back towards the rear tank, or the line from the rear tank to the selector valve, being bone dry probably, lets air get into the line between the selector valve and the lift pump. It doesn't stall or idle rough, it kind of acts like it's going to stall but catches again, all within 1 or 2 engine rotations, so it's very quick so there's no time for it to actually stall.
 
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Cubey

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Well I made a big mess (of myself) trying to put in a small engine filter I already had, but it was too small for the hose leading to the lift pump. I replaced the cracked, soft old hose that was bypassing the missing water separator in the process, with new Gates hose I already had on hand. I cut the old hose then realized it was too big for the filter. Wasted a bit of good bit diesel to the ground (and my hair) that was in the line leading from the selector valve.

After I replaced the hose, I decided to be brave. I started the engine, preset to rear tank. It started perfectly fine and idle sounded fine too. I let it idle for at least 30 seconds and gave it a little throttle a few times too. It didn't stall or stutter like it had air in the lines. Either the valve isn't actually switching, or it's just seamlessly changing and the fuel in the rear tank is usable.

At idle, I tried switching back and forth and there was no difference in idle and were no stutters or stalls. Is that how it operates when it's working properly? I've never used dual tanks.

If that sounds normal, I guess I will dump in an overdose of Howes additive but no extra fuel. It's about 20 miles to the next gas station I plan to refuel at, so the rear tank can slosh around and get the additive mixed in. Then I'll fill the front tank only, select rear tank and try driving it 25-50 miles that way. The gauge should drop noticably from it's current half a tank reading in that amount of time if it's using the rear tank. If it doesn't move, but switching to the front tank shows a drop from being completely full, I'll know the selector valve isn't working.

I don't really want to pump any fresh diesel into the rear tank until I'm sure the selector valve is working. I'll only lose a few ounces of additive this way.
 

IDIBRONCO

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My only experience with this was in my current truck. I bought the truck in January 2013. When I got the truck, I topped off both tanks before I drove it home. The gauge didn't read on the rear tank so I didn't use it. About 6 months later, I was putting a bed on it (I bought it with out a bed just for parts and then decided to keep it). Since the front tank read empty at about 1/2 tank, and I wanted everything to work so I swapped put the senders from both tanks out of my first F250 which was already wrecked at the time. I had hauled off what was left of the truck for scrap, but kept both tanks. While I had the sender off of the rear tank, I shined a flashlight inside and the fuel looked cloudy so I never used it. By around three years later, it had developed a hole in the rear tank and the full tank was not empty so I guess I did the right thing by not using that fuel.
 

IDIBRONCO

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Now, after thinking about it, one time in Dec of 2015, I did actually hit the FSV by mistake and switched back to the front as soon as I realized what I did. The FSV stuck on the return part and would return part of the fuel to the rear tank instead of the front. A month or so later, I drove the truck for the next time and I went through 3/4 of a tank in 94 miles. I found out that the tank was empty a few months later when I decided to bypass the FSV and use only the front tank. What I thought was fuel running out the vent in the top of the rear tank on that trip was probably fuel running out the hole in the tank.
 

u2slow

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The old fuel I've used just seems to get darker with age. I've had summer fuel gel on me come wintertime... it can get like white candlewax at the bottom. Early stages might be cloudy. It goes back to normal when it warms up.

I've fed my trucks old diesel, old furnace oil, waste engine oil.... no suprises... (knock-on-wood)... yet. Always some level of filtering though.
 

Cubey

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I guess dual tanks is just not worth the hassle, huh? I wish I could use them, but I guess it might just cost me a lot to keep it working properly. The replacement valve (requiring a different wire harness wired in, included) is $76 from O'Reilly. It has a lifetime warranty, but it would be a hassle to replace often if it repeatedly fails, like I've heard they do.

https://www.oreillyauto.com/detail/...50-econoline?q=fuel+tank+selector+valve&pos=1

In a way, I'd rather run on the rear tank, being 22 gallons instead of front 18. That's an extra 35 miles. What I have done before to get me to a cheaper station outside my range is to just add a few gallons of higher cost fuel, enough to get me to the cheaper station down the road. Every 10-20 cents per gallon counts!

I don't go out of my way though, it would cost me more. Even just one mile out of my way to save 5 cents per gallon is a lost cause.

Always some level of filtering though.

Before the FSV/lift pump you mean?
 

Cubey

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This thing got the about the same MPG, of not worse city, when gas was $3.50-4+

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It was cool looking and was thick fiberglass on the top and rear, but OMG the MPG was deadly for how small it was. 19ft long, Chrysler 5.9L 360 V8 2 barrel carb, A727 3 speed A/T, 3.55 rear end. I don't now if it was a carb problem or what.

I lost soooooo much money for selling that thing. ;Pissed
 

IDIBRONCO

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I've been told by Dodge guys that "a 360 just plain drinks gas". These same guys also had 318 Durangos that only got 14MPG so I don't want to think about what a 360 would get if they're right. For some reason, they were happy with the mileage on their Durangos.cookoo
 

Cubey

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A couple at this RV park said their newer E350 Class C (maybe 22-23ft?) with a V10 and a 4.54 rear gets about 9 mpg highway. Of course it has modern fuel injection, highly computerized controls, and a 4 speed OD A/T. Plus it's a lot lighter, I would assume, being at least 4ft less long. It is a bit taller than mine, though.
 
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