I just bought a '06 F450 crewcab 4x4, and was wondering if (1) you can harpoon the 40 gal aft of axle tank. (2) Does it help as much as with the pickup tanks?
This truck appears to have been equipped with the aux midship tank, but it's not there anymore. Will a larger tank fit there in lieu of the 19 gal tank? I was thinking if I put in another tank, it might as well be a big one.

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Thanks,

John

 

What you mean by harpoon?
40 gallons for economical diesel is pretty big tank. Mine is about 32 gallons and gives me 400 miles range empty.
Doing long haul, I am putting 100 gallons aux tank on the bed, but this is due to fact that where I live the fuel prices can be 40 cents higher than in next state. One fill up there can save me $50.
Just noticed that we are neighbors
Fill it up at Westley truck stop, or Lodi whenever you are in the area.
You know you have to get CA number and weight stickers on your ride?

 

Not sure if you can harpoon that tank or not. I've not seen anything in the Tech Folder or posted about it. For the replacement midship tank, check out Transfer Flow or Titan. I know Transfer Flow has them and I think Titan may have as well.......$$$$$ though.

Here's the link to Transfer Flow: http://www.transferflow.com/ford_chassis_tanks.html

The harpoon mod is popular with the pickups. It's a method of modding the tanks in order to get more fuel in them before they fill up the filler tube and cut the pump off.

 

I knew the "harpooning" term from RV where people were cutting off lousy left long vent pipes in holding tanks -lowering their capacity.
My 32 gallon tank is pretty tricky. What I noticed that filling up by gravity from my bed mounted tank I can squeeze good 7 gallons more in it, than foaming nozzle at pump can.
But lowering the air cushion in the tank can be dangerous in CA heat.

 

Yeah, but diesel has a very low expansion, the expansion is about .0005 per degree F. So, if you filled your tank (32 gal) in 50 deg weather and the temperature rose to 100 degrees, this would result in an increase of only 0.8 gal. Mind you, that's based on the temperature changing 50 degrees.

These trucks use fuel like we do air so just going home from the fuel station will offset that.

 

That aft tank you have, is it a plastic tank like an Excursion, or a steel tank like a chassis cab?

We harpooned an Excursion tank, and it definitely helped, and the construction was very much like the midship tank. But if it is a steel tank, then I have no idea.

 

The tank is steel. I'll have to wait until the weekend to crawl under there with a flashlight and mirror to see how the sending unit is attached.
I've looked at the Transfer flow tanks, and they are more money than I want to spend. I was wondering if a 38 gal tank out of a pickup would fit, the position of the crossmembers would be the main issue. I noticed that the filler tube goes through a hole in the frame, so that might preclude a tank that wasn't made to fit a chassis cab.

 

BTW, Got a chance to perform the Harpoon mod on my truck this weekend, finally. Then performed the maiden fuel up to test it out. Got all but 1 gallon in before the pump shutoff. The last gallon required me to slowly fill like we used to. In and out of the station in under 5 minutes, that includes logging my mileage.

 

I don't think a pickup tank will fit. the frames are slightly different between the 450/550 and the "little" trucks. I beleive the 450 has a 3" narrower frame. if you check the tranferflo site it show that the midtank numbers are different. I have the 40 gal OEM aft tank and the transferflo 50 gal mid tank. saw the 56 gal F350 tank and it wouldn't have fit, it was too wide.
Barney

 

Could some one explain about harpooning a tank and can it be done on a 2004 SD 250?

Thank you.

 

Welcome to guzzle's In-tank Harpoon Mod Web Page

 

Thank you Sir!!!

 

Pappy, It requires dropping the fuel tank, opening it up and cutting the vent tube from the inside. Allot of the How-To's explain cutting both is needed. When in fact, only the vent tube (smaller) is required to be cut. By shortening the smaller vent tube, you allow the tank to displace air quicker as it's filling. This allows you to get more fuel in the tank before the shutoff valve on the hand pump kicks the pump off.

Take a look at the following thread, post 8 for written instructions on the process,
https://www.ford-trucks.com/forums/2...-the-tank.html

The following links have plenty of pictures to go with the instructions.
Ford Powerstroke Diesel Forum
Ford Powerstroke Diesel Forum
Dropping Fuel Tank - Ford Powerstroke Diesel Forum