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This may have been addressed before but I want to throw it out there concerning the Harpoon Mod.
Is is possible the tube some folks elect to cut off is there to create a void in the tank to allow for expansion when it gets hot out?
All my fuel cans have a fill to mark for that very reason. We can't see into out tanks to verify a fill to point, so maybe this extended tube is there to create a automatic fill to point.
Just Thinking! While I was in my tank, I elected to leave mine intact for that reason. As far as getting more fuel I find a station on nearly every corner.
Any thoughts on this?
There are at least 2 vent lines, plus the one in the filler neck on the tank to allow for expansion. A station at every corner is good for someone that does not travel out west where there may not be a stop for 100 miles or so. Having the ability to carry 75 gallons (OEM + auxiliary tanks) of diesel fuel allows me to stop when and where I want instead of when I have to. When towing heavy or a large camper long distances, having an extra 5 gallons could help a lot.
In the picture below you can see the two vent ports which are the very bottom and the very top. Then, if I remember correctly the yellow port is the vent line for the filler neck, but I don't remember for sure. This is a picture I took while doing the Hutch/Harpoon mod on my truck.
In researching this a little further I found all manufacturers must install a means to restrict filling a liquid tank to 95% of capacity.
This regulation is" U.S. Department of Transportation Federal Motor Carrier Safety Administration Regulation 393.67 Subpart E.
This regulation in part is designed to prevent fuel spills on the roadway.
All vehicles do have vents to allow air to come in to offset the fuel going out.
If you remove this design of the tank and the fuel will expand, it is going on the highway.
This may not have a huge impact on the modified vehicle but the motorcycle rider that hits that fuel on the highway may have another opinion about that.
I can attest to this first hand. I was on a road that appeared to be perfectly dry. It was determined I hit diesel in a curve.
I suffered from a broken neck, 3 fractured ribs and a punctured lung. Fortunately I was wearing a carbon fiber helmet and a very heavy leather jacket.
I am just saying before making some mods we should think how is is going to impact someone else.
I too rode motorcycles for many, many years and I can say that I never ID'd a spot of diesel on the road. I can also say that if you had your tank pulled by the DoT, then the least of your problems is the fact that you cut 4" off the filler tube into the tank.
To each there own in regards to this mod. I am glad I did it and it will remain that way. If you are more comfortable with the tube extending into the tank, it is your truck, leave it that way.
I hope this satisfied your curiosity in regards to thinking about the harpoon mod.
Before I did mine and every time I fueled up I would get diesel splashing out when the nozzle would shut off, not so after the mod. The way I see it is by doing the mod I have solved an environmental problem, with a bonus of a little extra fuel purchased thus adding to the economy.......Its all good.
Ed
My understanding is to save some production cost Ford used the same fuel tank in both gas and diesel trucks. Gasoline expands more than diesel with temps plus needs more room for vapor, hence the design we have. Diesel pretty much just lays there in comparison. So by cutting the tube we can use the space built into the tank for more fuel without risk of overfilling.
And like Ed, no more foaming mess out the fill tube stinking up your Ariats on a hot day.
I have always filled my tank until I can see fuel at the top of the filler neck, and have never once discovered any signs of overflow being spread all underneath my truck (regardless of whether it could be due to either expansion or sloshing). If it were overflowing, there would certainly be signs of it just like when my HPX oil line started leaking at the fitting and coated the entire underneath of the body and my tailgate. I can say that same thing for my Excursion which shares the same mods. I've probably put at least 160K miles on my truck and at least 50K miles on my Excursion since making these mods.
Fuel in my town is on average. 80 cents more than the Reno area so that is where I fuel up. The closet station is twenty miles from home so by the time I get home I have my "expansion" room. I also fill into the neck and am glad I did the mod.
I was curious and did a little more research on the differences of thermal expansion between gasoline and diesel fuel. I found the coefficient of thermal expansion for gasoline on answers.yahoo.com and wikipedia.org.
Diesel Gasoline
coefficient .00083 .00095
Same -7 Deg. C (20 Deg. F) to 38 Deg. C (100 Deg. F) temperature increase as above.
1 Gallon 1.03735 G 1.04275 G Difference of 0.0054 G (~= 4 tsp.)
Same 25 Gallon tank as above.
25 Gallons 25.93375 G 26.06875 G Difference of 0.135 G (~= 1/8 G)
% of total 3.735% Expansion 4.275% Expansion 0.54%
I take to mean that what you mentioned is technically correct that diesel expands less than gasoline but, he is very inaccurate describing diesel as expanding "much less" than gasoline. Looking at the comparison objectively, I would say that the thermal expansion of diesel and gasoline fuels are comparably similar rather than noticeably different. In fact, I would interpret the numbers as: "they both expanded one gallon in the 25 gallon tank."
information from another site covering this topic "Seminecis"
Last edited by oldboots1950; Mar 15, 2016 at 08:23 PM.
Reason: update
The only time mine leaked was when a rust hole formed in the filler tube right at the spout. I replaced it when I did the H&H mod last year. I enjoy being able to fill the tank without all the foam. I used to baby it and get about 7 to 9 gallons in it after the first shut off. Now, maybe 2 gallons after the first shutoff and it's at the cap.
I have always filled my tank until I can see fuel at the top of the filler neck, and have never once discovered any signs of overflow being spread all underneath my truck
I have done this with all of my vehicles, gas and diesel, for over 34 years and I too have never had any signs of overflow.
Originally Posted by DieselDenny
Very fine examination of the mod.
You and I have very different definitions of "fine examination" when it comes to applying that term to someone thinking out loud.
Originally Posted by oldboots1950
I am just saying before making some mods we should think how is is going to impact someone else.
I applaud Boots'
No clapping of hands here. mostly just an eye roll.
Not flaming, so I hope nobody gets their bloomers twisted, just a disagreement on the stated opinion.
8 years and counting on mine. Never leaked (filling up, on-road, off-road, etc.). Even when I've topped off then hit the trails I've never had any spill out. When I fill up I can see it froth up the tube and that's when the handle auto-shuts off.
The fluid expansion is so minute, it doesn't factor into what can fit into the tanks of our size. It's the sloshing while driving that can be an issue, and a spill means we need to address the balance tube and fittings on top of the tank - because it will spill with or without the Harpoon mod. Diesel on the road that leads to a very harmful motorcycle accident could have come from a leaking tank, a damaged fuel line, a leaky fuel can in the bed of a truck, or some other cause far more probable and common than a Harpoon-modded Superduty.
I can't swear on a stack of bibles that the Harpoon mod won't lead to a spill - but I'm modded, and the outside tank surface is downright arid every time I've been under the truck.
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