Dodge Crew Cab fuel tank

[JHolt]

Fellow Crew Cab converters, I have a fuel tank question for you.



I have been using the original (gas) fuel tank in my crew cab conversion for a while, but recently got some bacteria in the fuel system, and while figuring it out, decided to take the tank out. While it's out, I thought I'd try to put in the fuel tank from my '92 (the donor truck) so the gauge will work properly (I put in the complete wiring harness and dash from the '92 and the sending units have completely different dynamic ranges). I could also then use the original plastic fuel lines that connect nicely to the lift pump and return line, and the diesel tank has a different fuel pickup system that looks better than the gas one. But the diesel tank won't fit properly because it was designed for an extended cab truck. The front part of it would hang down below the frame, which I don't like. I could lift the body of the crew cab a couple of inches, but I don't like body lifts.



Have any of you made that work, or are you just running with the tank that came in the crew cab from the factory? If so, did you find a solution for the gauge (assuming you switched over the instruments)? It doesn't look like I can take the '84 gauge and put it in the '92 instrument panel.



Thanks,

Jack

 

[PJensen]

Good Question there,



I am in the process of getting parts ready to convert my 83 CC 4x4. Stripped the 91. 5 truck last week, so Im on the way. I seen that the diesel tank has the bump in the front section.



What have you guys done for a lift pump that retain the gasoline tank? Just get a Holley or Mallory street pump and some braided fuel line?



I seen that there are 2 fuel lines. One is obviously supply is the other a return or a vapor line?



Thanks in advance



Paul

 

[JHolt]

So far I've been using the mechanical lift pump that is on the Cummins, it has worked just fine. I used the metal fuel lines that were already in the truck, the only problem was that they went to the wrong side of the engine. I bent them to come around behind the engine, and extended them with some standard rubber fuel line (and later added a second piece of metal fuel line to reduce the length of rubber line). Yes, the smaller diameter line is a return line, the diesel pumps a lot of extra fuel through so the return line is important.



I am still trying to figure out if I can get that diesel tank in there, with that damn bump on top (without the tank hanging down). Of course a while back I went and cut off the connector from the diesel electrical harness so I could connect to the sending unit from the gasoline tank, and now I can't find that connector!!

 

[Hutchew]

What I did.........

was use a fuel tank from a fuel injected gas motor truck, 93 model shortbed (I THINK it came from a shortbed, it was already out, and had 93 dge sb written on it). It will hold right at 29-30 gallons, so someone with an owners manual can probably look up the capacities and tell whether it did indeed come from a shorty. And now I'll tell you why I did... ... ... ...

Like JHolt, I didn't want to body lift the cab in order to use the diesel fuel tank. BUT, there is a problem with using the original fuel tank out of the crewcabs. Fuel injected engines, including these cummins, don't like air in the fuel system. Older gas engines, carburated, didn't really care if a little air got in, because with the vent system, it would just bleed the air out. The fuel tanks for both the Dodge diesel and fuel injected gas motors have a "well" built into them that the fuel is drawn from, and returned to. It has a series of valves that allows the fuel to flow into, but not out of, this "well". The reason for this is that when your fuel levels start to get low, and the fuel is sloshing back and forth in the tank, or you are on an incline, this "well" will prevent the pickup tube from sucking air into the system, because it always has fuel flowing into it, either from the tank itself, or from the return line. You could run the stock crewcab gas tank, but you wouldn't be able to run the tank very low. You would have to find the level where you start to have problems, and keep it fuller than that. I hope all that made sense.

Also, the sending unit will work accurately with your gauge, if you changed the dash out to a late model (it does with mine, anyway).

I also just use the mechanical lift pump on the cummins for delivery, but I hear that it is prone to failure on my generation motor, so I may change it to electric if and when it goes ka-put.

I am running 1/2" delivery and 3/8" return lines, silicone rubber, on my rig. I was told that using the stock size lines in my crewcab could quite possibly hinder performance with the P7100 pump. It might not be a factor with the older pumps. I wish I could find the pics I took of the assembly, they would explain what I did a lot better. A writer I am not. :{

 

[83 crew cab]

I dont know why but the fuel tank out of the 89 2wd 3/4 ton long bed fit right in my truck I know from everthing I have heard that it should not have fit but maybe the 89 tank is differant George

 

[Joseph Donnelly]

I don't know the whole story, but I put an 81-up 30 gallon tank (20 was the std. size) into an 80 crew cab short bed. That swap is tough because you have to change the crossmember at the front hangers for the rear leaf springs, and cut out a bed "hat section" cross brace where the tank has a hump. I put a 2x2" box crossmember in where the 81 up had the hat section to regain bed strength on the '80 bed.

So, I don't know about early 90'sl 30 gallon tanks, but I think the early to mid 80s 30 gallon tank should fit. Stock midships tank up to 1980 was only 18 gallons, and extra capacity was achieved via an aft axle 21 gallon tank, moving the spare tire into the bed and mounting it with a bracket in front of the wheel well on the right side. If you have a short bed regular cab, I don't know if there is enough clearance. There should be, with the correct front mounting bracket/strap. The short bed trucks used a different tank front mount from the long beds, with the 30 gallon tank.

 

[JHolt]

stuffed it in there

Well, I just decided to try shoehorning that '93 30-gal diesel tank in there, and it worked out better than I expected. It kind of mashed that hump down a bit (front part of it, anyway), and it hangs down a little bit in front (maybe 1. 5"), but it seems to be in there just fine and the fuel lines hooked right up, I even found that connector for the wiring harness so it all works. I suppose the cab/tank contact isn't the greatest thing, but I also don't think it will be a problem. And there is so much ground clearance that the bit hanging down shouldn't ever be a problem. The transmission crossmember is quite a bit lower.



Hutchew, your explanation of the "well" in the diesel system makes a lot of sense. I did have problems when my tank got low (while using the gasoline tank). Since the gauge didn't work, I just went by mileage, and it seemed to start around 1/3 or 1/4 tank. Eventually it increased to 1/2 and then 3/4 tank but that was because I got bacteria in there and it was clogging the screen in the tank. That's what led me to taking it all out. So I don't know if that was part of the problem all along but comparing the (carbureted) gasoline and diesel fuel pickup systems, they are worlds apart and your explanation sheds light on why. Getting a fuel injected gasoline tank sounds like a good idea if it fits better. Apparently yours did!



Joseph, I thought about moving that crossmember back a little so the tank would fit easier, but just wasn't up for all that work. Maybe it was more critical for your early 80's tank, though.



Thanks for the input guys, I'll let you know if I have any problems with my installation.



jack

 

[JHolt]

hmmmm

yeah that makes sense too, that a shortbed regular (or extended) cab tank would work since it would have the same constraints on rear axle to cab distance. i wouldn't have thought they could get 30 gallons in there with the shorter overall length. I sure don' t know how your '89 longbed tank worked there, George, but glad it worked for you! Maybe those '89 diesel tanks really are different.



jack

 

[Joseph Donnelly]

Yeah, I had to remove that hat section on an 80 bed to clear the 81 up tank. You might find the hat section was moved again in the early 90s and that you can heat it with a torch and beat on it to get it out of the way. Mine needed to be cut out completely. Rubbing like that could wear a hole in the tank eventually. It sounds like you have the long bed front mounting strap or bracket. If you can scrounge up the stuff from a short bed in a junkyard, it should take care of the tank at the front. As I recall (this was about 14 years ago), the short bed L bracket does put the tank about 1. 5" lower relative to the frame vs. the early truck bracket, or the late truck 20 gallon stuff, that fits under the front of the tank.

Best wishes. Bring it to May Madness if you can.

 

[LarryB]

I use three different tanks in mine. All are gas tanks and I have not had a problem running them close to emply. I did have a problem with my biggest tank when I first connected the Cummins to the return line. There was some type of check valve in the pickup tube that could not handle the return flow. It would push the check valve open so far it would plug and blow the rubber line right off. Eeeewwww, what a mess!



On my most recent trip I began to have problems using this same tank. I think I also have something plugging the pickup screen. If I stopped and blew compressed air into the tank through the feed line it would work for a few miles. Guess I'll have to drop it and see whats swimming around in there.



#ad

 

[CrewCabDiesel]

Gee guys, just make it a 8 foot box too, then a standard diesel fuel tank fits (; . Just kidding, buy the way got my NV4500 installed, what a difference, don't reach over to the passenger's for reverse or hit the dash for 5th.

Kyle

 

[JHolt]

I was wondering when you would say that! Would certainly make it easier with the 8-ft bed.



I think I'll modify my brackets one of these days, so the tank doesn' t rub the cab. The brackets are from the '84 which is a shortbed. The '92 brackets won't work because they have specially shaped ends that fit into a notch kinda thingamajig for easier removal. The '84 doesn't have the receiving end for those.



Headin off to Mexico for the weekend, so I have to git loaded up and goin... no problems so far with the "new" fuel tank setup. And the gauge works!