I have been curious about the "harpoon" job that the PSD crowd has found useful. If you are not familliar with the procedure, apparently the vent tube extends a few inches into the tank on the new Super Duty's. On several Ford boards they are talking about dropping the tank and trimming the tube with a pair of pvc cutters.

I finally ordered a small fuel/tool combo box and was interested in plumbing it directly into the main tank, so I decided to drop my fuel tank today to have a look. On our 3rd gens the vent tube is cut on an angle inside the tank, and the high point of the cut is about 1/2" from the top of the tank. I do not believe that there would be any benefit to be had by attempting to trim it any further. What would probably work to help the foaming problem would be to add a bulkhead fitting at the high point on the tank and tee it into the vent tube line. Strangely, the 3/4" vent tube is a couple of inches lower than the high point on the tank. There is a small breather valve outlet at the high point, but it only has a 1/4" barbed outlet.

FYI for anyone wanting to plumb in a transfer tank, there is a barbed 5/16" fuel fitting that is capped just in front of the connector for the fuel guage. It is meant as an alternate pick-up point because it has a hose on the inside of the tank that goes to the bottom. I removed the internal hose on mine becuase I only intend to use it to fill the tank.

 

[quote author=Nevada link=board=17;threadid=23372;start=0#msg219448 date=1070772927]
Strangely, the 3/4" vent tube is a couple of inches lower than the high point on the tank. [/quote]
Not so strange. That design prevents fuel expansion from causing a leak. Fuel comes out of the storage tanks at the station at 55 or 60 degrees even when the outside air temp is 100 degrees. The engineers have to consider the possibility that you could pull into a truck stop nearly empty on a hot day, fill the tank, and then park for an hour to get lunch. The fuel will expand as it warms up, and it has to go somewhere. That's why there's an air pocket designed into the tank.

 

Good point Wannadiesel. I wonder how this air pocket figures into the fuel tank capacity.

 

Hijacking this thread slightly...
Maybe this partly explaines poor fuel economy in the winter if not for diesel then gas engines.
Fuel comes out of the ground at 55 or so degrees and chills in your tank until 0 or so. One would have to assume the fuel would contract.
Although... the very process of fuel injection heats the fuel well beyond outside summer air temperatures anyway. but maybe not for gas engines.
Confused?? I am...

 

Nevada, when you do the install, could you take some pics for us?

 

[quote author=bulabula link=board=17;threadid=23372;start=0#msg219514 date=1070802562]
Nevada, when you do the install, could you take some pics for us?
[/quote]

I do have access to a digital camera, but have never used one. I guess it's time to learn. I should be able to do the install before the holidays, I would be happy to TRY to post some pics.

 

[quote author=wannadiesel link=board=17;threadid=23372;start=0#msg219454 date=1070773727]
[quote author=Nevada link=board=17;threadid=23372;start=0#msg219448 date=1070772927]
Strangely, the 3/4" vent tube is a couple of inches lower than the high point on the tank. [/quote]
Not so strange. That design prevents fuel expansion from causing a leak. Fuel comes out of the storage tanks at the station at 55 or 60 degrees even when the outside air temp is 100 degrees. The engineers have to consider the possibility that you could pull into a truck stop nearly empty on a hot day, fill the tank, and then park for an hour to get lunch. The fuel will expand as it warms up, and it has to go somewhere. That's why there's an air pocket designed into the tank.
[/quote]
Actually, diesel fuel doesn't expand/contract much at all with temperature variance. We really don't need that extra air expansion space in our tanks. I bet it's there in the production line because the gas models DO need it.

This exact thing happens with VW tdi's. They leave some airspace for thermal expansion of gasoline etc, and the parts were not re-engineered, they were just carried over to TDI diesel models. Several , if not most of the tdi'ers have removed their fuel tank venting system by removing a button in the filler neck. Nobody has had a problem, and I personally have filled my tank up to the cap (no airspace) and let my dark blue TDI sit out for 8+ hours in 100F florida sun (this is on purpose for testing) and after opening the cap the fuel level hadn't moved even a tiny bit, there was no pressure release hissing like a gas cap sometimes does etc.

If there were a way to somehow remove the tank's ability to leave that airspace, that would be the fix to our p roblem.

Sorry didn't mean to hijack the thread being slightly off topic, its' just there have been several threads going on how to beat this foaming problem, and this is great info.

 

[quote author=Lightman link=board=17;threadid=23372;start=0#msg219593 date=1070818783]
[quote author=wannadiesel link=board=17;threadid=23372;start=0#msg219454 date=1070773727]
[quote author=Nevada link=board=17;threadid=23372;start=0#msg219448 date=1070772927]
Strangely, the 3/4" vent tube is a couple of inches lower than the high point on the tank. [/quote]
Not so strange. That design prevents fuel expansion from causing a leak. Fuel comes out of the storage tanks at the station at 55 or 60 degrees even when the outside air temp is 100 degrees. The engineers have to consider the possibility that you could pull into a truck stop nearly empty on a hot day, fill the tank, and then park for an hour to get lunch. The fuel will expand as it warms up, and it has to go somewhere. That's why there's an air pocket designed into the tank.
[/quote]
Actually, diesel fuel doesn't expand/contract much at all with temperature variance. We really don't need that extra air expansion space in our tanks. I bet it's there in the production line because the gas models DO need it.

This exact thing happens with VW tdi's. They leave some airspace for thermal expansion of gasoline etc, and the parts were not re-engineered, they were just carried over to TDI diesel models. Several , if not most of the tdi'ers have removed their fuel tank venting system by removing a button in the filler neck. Nobody has had a problem, and I personally have filled my tank up to the cap (no airspace) and let my dark blue TDI sit out for 8+ hours in 100F florida sun (this is on purpose for testing) and after opening the cap the fuel level hadn't moved even a tiny bit, there was no pressure release hissing like a gas cap sometimes does etc.

If there were a way to somehow remove the tank's ability to leave that airspace, that would be the fix to our p roblem.

Sorry didn't mean to hijack the thread being slightly off topic, its' just there have been several threads going on how to beat this foaming problem, and this is great info.
[/quote]

Sorry to disagree with you, but if you eliminate the air space, which is against federal law, you will have fuel all over the driveway after filling up. Federal law calls for no more than a 95% fill to allow for expansion.

 

What do you think we're doing when we sit there at the station and take forever filling it all the way up to the cap? Fuel never spills out. Maybe I dont understand what you're trying to say Haulin. I do know that in 99% of forum member TDI's theyve eliminated the venting and fill to the top every time. Where would you think it would spill out of?

 

Its a free world, you can do it as you want, but. Fuel tanks are designed as regulated by federal law, you cannot fill them over 95% so that expansion will not leak fuel. On the 2nd gens the tank has a hump above the filler that cannot be filled. Diesel fuel does expand and will push out somewhere. Look at a big truck tank, the filler is not at the top and has a tube inside that extends into the tank so that it cannot be filled all the way. Saying that the fuel does not expand is rediculous. If you defeat the expansion capabilities in the tank you may get away with it most of the time but the fuel will expand and leak. Really tears up a blacktop driveway.

 

Well thats an interesting theory. Ever have a 5gal can of diesel and gas in the sun for a few hours? Ever notice how the gas can is puffed out like it's going to explode and the diesel is no different than when they started? I have. Diesel doesn't expand nearly like gasoline, and I see no problem with filling to the cap. Maybe there is some small amount of airspace built into the tank for a safety measure as you say, but it doesn't need to be 5 gallons worth, which is what you're able to squeeze in after the first click....

 

Lightman, how long does it take to top off after the nozzle clicks off? My Ford takes a long time to top off both tanks. I usually give up after alternating between the two tanks several times. Hopefully the Dodge will be faster.

 

[quote author=Lightman link=board=17;threadid=23372;start=0#msg219634 date=1070824975]
Well thats an interesting theory. Ever have a 5gal can of diesel and gas in the sun for a few hours? Ever notice how the gas can is puffed out like it's going to explode and the diesel is no different than when they started? I have. Diesel doesn't expand nearly like gasoline, and I see no problem with filling to the cap. Maybe there is some small amount of airspace built into the tank for a safety measure as you say, but it doesn't need to be 5 gallons worth, which is what you're able to squeeze in after the first click....
[/quote]
Lightman- You're confusing two separate issues, vapor pressure and expansion. Gasoline has a much higher percentage of light fractions that gasify at high temps, which causes the pressure in your example can, not the expansion. You won't harm anything by filling the tank as full as you can get it in its stock configuration, (you still have that 5% air pocket) but if you put the vent at the high point in the tank so you can fill the air pocket you will have problems.

 

What about altitude change ? Does fuel expand the higher you go? I use to start loosing gas on my full tank after an increase of 3000 to 5000 feet.

John

 

When I had my aux tank in the 98 Ram I had the vent tube extend up to the bed and into the aux tank.
When I filled the factory tank I did not have a much foaming...some of the foaming simply comes from the churning of the fuel in the tank...most of the bubbles disapated sp?] up the vent tube and into the vented aux tank. I could hear the burps/gurgles.

On my 04' I am going to extend the vent tube the same way.
I also have an additional pick up in the aux tank for the ESPAR heater and/or other things that need diesel fuel.
I tapped into the main filler tube of the factory tank from the aux tank and that was my transfer line to the factory tank.
I run a Carter pump to take the fuel from the aux tank [from the top of the aux tank via a dip tube fitting] through a filter and into the factory tank.

Way back...I had a 90 Ram with a an aux tank...gravity fed.
I had vented caps that where extended 3" above the top of the tank. Even though they were vented, if the tank was less then full and I removed the caps...they hissed some.
I also had to loosen a cap when I opened the gate valve to dump fuel to the factory tank.

DOT in the USA politely told me that the gravity feed tank was illegal there and the only reason I got a warning was because I was from Canada eh. Otherwise a fine and even the removal/disconnection of the tank would've happened. Its all pump fed and top supply now. ;D

I think I just might get this tank installed this year.