D21 fuel tank swap?

bpayne · Sep 22nd, 2006, 09:24 PM

OK, I've searched around and could not find any reference to this sort of thing, so I figure I'll throw it out and see what comes back.

My fuel tank is pretty well rusted, and needs to be replaced. I figure, if I'm in there, why not replace it with a tank for a V6 truck and get more fuel capacity. I assume that I would need to replace the fuel pump/sending unit as well to deal with the larger tank. But I'm concerned that I may have to replace the pump anyway, as from what I can see the top of the thing is scaly rust - so the extra cost may be a necessity. I'm afraid of what is going to happen to those little bolts that hold it in, as well as the hard lines for output and return. Plus, if I'm going to spend the money, I might as well see some other "benefit".

My questions are:
1. Has anyone done this swap or a similar one?

2. Dimensionally, the two tanks shouldn't be different enough to cause a problem since it is for the same truck, i.e.: the frame crossmembers and bed clearance shouldn't be an issue...Correct? I understand King Cabs are different from Standard.

3. Does the V6 tank have a fuller shape to the top, or does it have a deeper sump? Perhaps the same pump would work if the tank were fuller overall, just my fuel gauge would be a slightly different sort of incorrect than it is now. Is the difference only in the float for the gauge? I assume not, which leads to number 4...

4. The specs in my crummy Haynes manual show the pressures to be identical without vacuum and the V6 pump putting out one more psi with vacuum. I'm not sure exactly what they mean by with vacuum vs. without, can anyone clear that up? Shouldn't the fuel pressure regulator deal with it to make the rail pressure correct anyway, since worst case it is a slightly higher pressure than the current pump? Digging around NAPA, Autozone, and Advance to compare 4 and 6 cylinders was not conclusive. Some have identical part numbers, some do not.

5. Opinions on OEM vs. aftermarket fuel pump quality/longevity?

Comments, suggestions? I'd be honored to have 88pathoffroad stomp me a new one.

Thanks, I appreciate any feedback that anyone can give.

**88pathoffroad** · Sep 22nd, 2006, 11:59 PM

As far as I know, the trucks only got one size tank, 15.9 US gallons. The Pathfinder tank (21.1 gallons) is in the rear and won't fit a pickup.

bpayne · Sep 24th, 2006, 11:46 PM

Thanks, I knew the Pathfinder tank would be incompatible. Somehow, I remember reading about a larger tank. Car-part.com offers a choice for V6 4x4 KC and claims a larger capacity, however there are much fewer listed in that category. And checking out the Chilton manual, I see that they do show all trucks as having 15.9 gallon tanks. They also explain that the fuel pressure in more detail. The difference is between applying vacuum to the pressure regulator, and no vacuum applied. Makes sense now.

Unless someone with a V6 pickup confirms they have a larger tank, I have to give up on the idea.

I suppose the only curiosity left to this fiasco is if anyone knows of a source for new mounting plates for the fuel pump? I hate to waste cash on a whole new fuel pump assembly when mechanically the pump is OK. Right now I just have to take care not to trash the corroded one when swapping it to the new tank, but I would much rather replace it if possible.

bp

**88pathoffroad** · Sep 25th, 2006, 02:04 AM

The pump is not part of the cover and fuel level gauge assembly. It's removeable.

Vertigo1 · Sep 26th, 2006, 12:00 AM

If I remember correctly, the tank in my '96 V6 4x4 hardbody is about 22gallons, including the filler hose. I know I've put in as much as 19.5gallons at one shot, so its definitely bigger than 15.9gallons.

bpayne · Sep 26th, 2006, 08:52 AM

Oh, cool. Thanks!

Would you or anybody else with a V6 4x4 KC be willing to take measurements (at least on the depth of the tank) to help determine if I would absolutely need a different fuel pump to reach the bottom?

Much appreciated,
bp

Fred S · Oct 4th, 2006, 12:41 AM

Quote:

Originally Posted by Vertigo1

If I remember correctly, the tank in my '96 V6 4x4 hardbody is about 22gallons, including the filler hose. I know I've put in as much as 19.5gallons at one shot, so its definitely bigger than 15.9gallons.

Vertigo,

I own a 95 V6 4x2 and my tank capacity is 15.9 gallons. Either the tank changed in 96, or the 4x4's got a different tank..

Fred

bpayne · Dec 14th, 2006, 12:15 PM

Thanks for the input. Just wanted to follow up and let people know the swap has been completed.

The short answers are: Yes, the 4x4 V6 King Cab (were they all King Cabs?) has a 21 gallon tank. And yes, it will bolt in to the 4 cylinder King Cab 4x4 truck. Very easily in fact, if you can find a junkyard that doesn't destroy the mounting brackets during the removal process. However, I cannot speak to 4x2 compatibility. I've never looked underneath one to see how things compare.

The V6's tank is longer, so the bolted-in front mount that comes off the passenger frame rail needs to be removed. Instead, the tank's front bracket attaches to the crossmember that also supports the driveshaft. Of course, this whole thing could be done very easily if you can get the front mounting bracket from the donor truck. I didn't feel like giving Nissan $110 for some steel that had the right shape, so I made one that fit.

I'll leave out the other fun stuff that will surely go down in history as "The Gas Tank Fiasco."

If anyone wants more details, let me know. I have pictures if you're interested.

If one was making a checklist when buying a Hardbody, the rear of the upper half of the fuel tank should be on it. Crud gets packed between the tank and the rear mount over time and promotes rust, at least in areas where salt is used in the winter. I will be blasting that area with the hose periodically.

bp

Vertigo1 · Dec 17th, 2006, 12:26 AM

Yeah, I knew it was 21 or 22 gallons. No one wants to listen to me. Ahh, so like the rest of my life... heh