Bigger or dual fuel tanks...

[74M35A2]

After 6 hours of driving, you don't need to eat/walk/take a leak?

 

[jspanier]

i'll post it soon. The truck is still in fab. I've ask my welder to take a picture for me. I'll post it as soon as I get it.

 

[Another Ahab]

i'll post it soon. The truck is still in fab. I've ask my welder to take a picture for me. I'll post it as soon as I get it.

 

[Csm Davis]

Doghead many of the hydraulic tanks are mounted behind the cab so that's an option for moving it. Also I would not run a crossover or put two tanks together that's putting all your eggs in one basket, just one leak and you are done. The stock military dual tank system works well and why not use it? It has saved my bacon many times, forget to check your fuel, knock a hole in a tank, switch tanks and keep rolling!

 

[74M35A2]

I would not do a cross over due to the possibility of overflow on the lower tank if you park on the side of a hill. My tank is always empty anyway, but just sayin'....

 

[4x4 Forever]

Or possibly a pump to transfer out of one to the other.

The one large tank made from 2: you might want to investigate the guage of the metal to see if it is think enough for such a large tank. Has anyone looked up the CFRs for fuel tanks: metal guage sizes, capacities, etc.? I would not want to see someone going down the road and loose a tank of fuel...

 

[Csm Davis]

Or possibly a pump to transfer out of one to the other.

The one large tank made from 2: you might want to investigate the guage of the metal to see if it is think enough for such a large tank. Has anyone looked up the CFRs for fuel tanks: metal guage sizes, capacities, etc.? I would not want to see someone going down the road and loose a tank of fuel...

I don't think it will be a problem welding the two together if done professionally, which he is having done. But I would have it baffled to slow the sloshing of the fuel. One problem with such a long tank is the pickup it is going to be uncovered much worse than the stock.

 

[jspanier]

I'm adding two extra brackets in the process. I would not attempt to hold the load with the existing brackets. That's asking for trouble.

 

[turnkey]

Just go to your freindly Mack truck store and buy 2 ,120 gal SS fuel tanks...Heck, they will mount them also....Done and on the road again..Used the same releif system they put into long range plans for pit stops....

 

[74M35A2]

Don't use stainless steel on a mobile application. Stainless is one of my favorite materials, but mobile fuel tanks are typically made of softer metal so they don't crack. Stainless steel is prohibited from use in marine fuel tanks specifically for this reason. I'm not sure, but the Mack ones are likely polished aluminum.

Extending the factory tank should be ok as long as it is supported well for the weight, the same material is used, and the weld is good. Probably simplest to make one large tank out of two smaller ones, cutting at the desired width, then there is only one single seam to connect.

 

[Csm Davis]

Don't use stainless steel on a mobile application. Stainless is one of my favorite materials, but mobile fuel tanks are typically made of softer metal so they don't crack. Stainless steel is prohibited from use in marine fuel tanks specifically for this reason. I'm not sure, but the Mack ones are likely polished aluminum.

Extending the factory tank should be ok as long as it is supported well for the weight, the same material is used, and the weld is good. Probably simplest to make one large tank out of two smaller ones, cutting at the desired width, then there is only one single seam to connect.

All 939 series trucks had stainless tanks.

 

[av8or]

I mounted 2nd tank on other side to get 220 gals. Connected together on the bottom, feeds well and the gage works well.
\

 

[Another Ahab]

I mounted 2nd tank on other side to get 220 gals. Connected together on the bottom, feeds well and the gage works well.
\

Hard pipe, or flexible connection?

 

[74M35A2]

All 939 series trucks had stainless tanks.

Really? Seems heavy and expensive vs aluminum. The paint is flaking off mine, maybe I'll kiss it with a grinding wheel and see if it sparks.

 

[av8or]

Hard pipe, or flexible connection?

hyd. hose inside of alum. tube.

 

[Csm Davis]

Really? Seems heavy and expensive vs aluminum. The paint is flaking off mine, maybe I'll kiss it with a grinding wheel and see if it sparks.

Don't do that, I have scrapped more of these than you have ever seen before. There are a few different prototypes running around that I haven't got my hands on but as far as 939 series trucks I have been in, worked on, scrapped, or towed over 2000 of them. So yeah really.

 

[74M35A2]

I believe you. Looked to be aluminum at first sight.

 

[tim292stro]

Depending on your location, vehicle weight, and registration style:

CFR Title 49 vol5 sec393.65 All fuel systems.
(a) Application of the rules in this section. The rules in this section apply to systems for containing and supplying fuel for the operation of motor vehicles or for the operation of auxiliary equipment installed on, or used in connection with, motor vehicles.

CFR Title 49 vol5 sec393.67 Liquid fuel tanks. (a) Application of the rules in this section. The rules in this section apply to tanks containing or supplying fuel for the operation of commercial motor vehicles or for the operation of auxiliary equipment installed on, or used in connection with commercial motor vehicles.

With a 5-ton, hauling a trailer with your toys on a trailer you're likely going to end up over 10Klbs and fiding your way into the commercial restrictions which are a harder target to hit.

...If possible I would mount them same height and run a good crossover tube at the bottom so they stay equalized...

...Just run a connecting line between the tanks as the fuel will self level, also run a breather line between the 2 tanks so as fuel transfers itself over air can move out...

I'm just going to say: AAAAHHHH!!!! This is probably illegal, vehicle classification dependent... CFR Title 49 vol5 sec393-65(d) "Gravity or syphon feed prohibited..."

...Also I would not run a crossover or put two tanks together that's putting all your eggs in one basket, just one leak and you are done. The stock military dual tank system works well and why not use it?...

Very good advice!!!

...I would not do a cross over due to the possibility of overflow on the lower tank if you park on the side of a hill...

CFR Title 49 vol5 sec393-67(12)(i) The tank cannot be filled, in a normal filling operation, with a quantity of fuel that exceeds 95 percent of the tank’s liquid capacity; and
CFR Title 49 vol5 sec393-67(12)(ii) When the tank is filled, normal expansion of the fuel will not cause fuel spillage.
And the EPA gets involved if you have a spill...

...Or possibly a pump to transfer out of one to the other...

Sure, fed from the top of the tank, can't violate the 95% max fill limit, both tanks need to be vented there needs to be a roll-over cut-off on the vent.

If you have a commercial classified vehicle, the tank needs to be certified and tested. The last part that kills this for me is the "Additional Information" from this page:

1. The 1990 Clean Air Act states that an individual owner of a vehicle may modify the fuel system only if it complies with all federal regulations. Failure to meet these regulations will risk state and federal penalties.
2. ...
3. Gravity feeding gasoline or diesel fuel from one tank to another, using a balance line, is illegal for all systems except ICC diesel systems. ICC is the abbreviation for the Interstate Commerce Commission, now known as the Interstate Operating Authority.
4. Replacement fuel systems are acceptable as long as they meet the previously mentioned regulations.
5. Should non compliance with FMVSS or the 1990 Clean Air Act be discovered, the owner would be liable for civil penalties up to $2,500 for each violation.
6. ...
7. ...