duck fan, when you did the harpoon mod on your Excursion's fuel tank how much of the vent tube did you cut off? Did you also cut the fill tube? Did you do it by yourself and how long did it take? Curious if you used a soldering iron or PVC cutter.

 

I'm not Duck Fan, but I've done the same already myself.

1. Vent tube... cut it ALL off.
2. Fill tube... I cut it off on my F250, will NOT do it on the Excursion.
3. Had my two sons helping with the 28 gallon tank, used my floor jack with a piece of plywood to lift the tank back up. Could have done it by myself. I would say that the tank job is about a 2hr job, but that can easily vary. Leave the top plastic tank ring in the sun so it goes back on more easily (expands with the heat), or you can soak it in almost boiling water for about 5 minutes and then dry it off and re-install. Also, use your fuel pump with the fule filter housing drain line open to make sure you get the tank as empty as possible before starting to remove the tank.
4. PVC pipe cutter works wonderfully and is much easier than trying to use a soldering iron where you can't actually see where the tip is, which would icnrease the potential for burning a hole in the tank liner.

 

It's always been a hot debate between those who cut both tubes (myself included) and those who cut only the vent. I am happy with having both cut, and I don't think you will gain any capacity unless you do cut both. I guess you have to do your searching and reading and decide for yourself.

 

I don't know why it would be a hot debate. I know that I certainly won't argue about it. What I will do is offer an illustration of what happens with the Harpoon mod and demonstrate why cutting the fill tube is at best of no benefit, and is more than likely counterproductive to the Harpoon Mod's objective. Often, pictures make it easier to see things than just words and explanations alone.

In the schematic below, the top picture is the OEM tank design. You can see that as the fuel level increases, any surface foam will hit the vent tube opening well before the tank is full. Once this happens, the pressure of the fuel entering the tank will force the foam up the vent tube until it re-enters the fill tube right at the filling nozzle. This is what causes the pump nozzle to shut off before the tank is full because it detects the foamy fuel coming from the vent tube and then shuts off to prevent overflowing your tank to the ground.

In the bottom picture, you can see that when you raise the vent tube's inlet to the top of the tank (by cutting it off), the tank can be filled more completely before foam is forced up the vent tube. This is why you can get more fuel into the tank at a faster pace before having to trickle in the last gallon or so.

Now, when you think about it, if you also cut the fill tube, you don't gain anything in terms of changing when the foam will rise up through the vent tube, except.... by raising the height of the fill tubes discharge point, you also create a situation where the fuel will fall farther, create more turbulence, and thereby create a little more foam than if the inlet actually became submerged as the tank gets full.

So, you can cut the fill tube if you want to, but you won;t gain any benefit at all from doing so. The negative impact of cutting this tube is probably rather small, so it's realy not worth any kind of argument.

 

If that is your drawing, well done, and very quickly too.

But the problem is this - the foam is not created by turbulence of the fuel stream hitting the surface. The foam is created by the pump nozzle itself. I know this for a couple of reasons. First is just by pulling the nozzle back and watching the aerated stream. Second, some nozzles are worse than others, and the ones that don't create foam are a joy to use. Third, you can tell by how fast the foam climbs the fill pipe that it is not coming from the surface.

So, if I'm right that the foam is created at the nozzle, cutting the fill tube off allows the foam to float away in all directions on the surface of the pool.

If you don't cut the fill tube, once the surface level reaches the fill tube, you can still add more fuel but the weight of the column of fuel in the pipe must push the pool of fuel upward as it flows into the tank. Gravity does that of course, but much slower than it would if it only had to push air out the vent. Cutting both tubes means that only air, and finally foam, must be pushed out the vent tube.

You are right about one thing, I should have said it was a frequent debate, rather than a hot debate. There is no point in getting worked up about it either way.

I know I gained a couple of gallons by cutting both tubes. But I will never prove it, because I don't ever want to run a Powerstroke out of fuel.

BTW, one quibble with your drawings, the vent tube already enters the tank at a point that is higher than the fill tube, so even if you cut them both, the vent will be higher than the fill.

 

Hmm, really got me thinking about the fill tube. Has anyone actually done this on a 44 gallon tank? Still wondering how manageable that skid plate and enormous tank will be by myself. And really wondering if I'll even be able to reach it all on such a different tank.

 

i dropped mine by myself with a floorjack...it wasn't that hard..i was doing some fuel system mods..i found a big clamp worked great to get the stubborn giant lockring back on..

 

Bill... yes, that was my hastily drawn sketch of the tanks, and a very simplified version at that. Your comment about the details regarding tube entry point elevation is well-made and much appreciated.

You've made a couple of good points, and I will have to concede to you on the issue of having the incoming fuel having to push against the slight head pressure of hte tank level if the fill tube remains submerged. That is one issue I had not yet thought through, and you're right. Regarding the foaminess coming from the nozzle, I know that you are right there as well. My only real point there was a proposition that the falling fuel would create MORE agitation and aeration, but again, the point about the air bubles scattering more widely rather than being more pointedly directed by a subnerged tube is an excellent one.

Therefore, I retract my proposal about not cutting the inlet tube, and will plan on cutting BOTH when I do this on my Excursion in the next couple of weeks.

William... great photo and excellent idea about using the clamp on the plastic ring.

7.3 Ex... if you get the tank empty, you can manage it by yourself quite well by using what both William and I have already mentioned... a floor jack and a piece of plywood... much, much more easy than you might think because the tank is plastic... a little awkward, but not unmanageable by a single person with a jack. Reinstallation is also a rather simple task, again, as long as you use the floor jack.

 

Thanks for the comments Pete, and I sure hope I'm right. It is what made sense to me, and I did not want to have to do the thing twice.

I added the photos of the Excursion to the bottom of my original page on the harpoon mod. It's been a year ago, so I hope my memory serves me on the details. If nothing else, the photos might help, although William already beat me to that too.

Here is the link for whatever help it might be:
Powerstroke Fuel Tank Modification

That Excursion belongs to a guy here on FTE, but I can't remember his handle. I met him through a different forum. I hope he doesn't mind me using him as an example.

 

How many inches does the truck need to be lifted to be able to slide the tank out from under the truck? I'm wondering if my 1' block and 37" tires would be enough. My driveway is on a short but steep slope and I don't have ramps. Was reinstalling as much of a challenge as the Super Duty truck guys say? Thanks folks, this is the help I was looking for. Do you guys think there is another flat spot on top of the tank to drop in a heat exchanger that has 4" of clearance above for coolant fittings?

 

WOW that looks like a lot of work...I give you mad props!!!!

 

Just to be clear...

This only applies to diesel tanks?

Is the gas tank a different design of does diesel just foam more...

Inquiring minds want to know....

 

It wasn't very much, but a few inches. It was a matter of the floor jack being under the tank, so we had to slide the tank sideways off the jack and under the body. Jackstands under the axle should work too.

Doubtful. See that black strip on the top of the tank in Williams picture? That is a pad that rests on a frame crossmember. There isn't much clearance above the tank.


Yes, diesel only. It is the same tank for gassers, but the gas trucks must have a vapor recovery system and must have an air space at the top. No vapor recovery system on diesel, so some of that extra air space can be used for more fuel. Gas foams less anyway, so slow filling is not really an issue for them.

 

Thanks for the quick response!

 

Just as another "Oh by the way"... I have found that diodiesel doesn't foam nearly as much as either #2 or ULSD.