Has anybody put their subtank on the roof? (1 Viewer)

[artech]

I'm trying to figure out where I'm going to put my new-to-me 21 gallon aluminum boat fuel tank which measures a nice low profile 36x18x7 inches high. I have a j-moose style roof rack sitting on 8 Gamviti mounts and the tank would fit nicely up there and the mounting would be very solid. It should ride pretty well since it probably would only get used a few times per year.

The tank is all aluminum and very light when empty. Be like having 4 jerry cans up there, only with just one manual valve and a straight gravity feed into the main tank. Would have to climb up to fill it up, but again, that would be pretty infrequent.

The main reason I'm considering this instead of the usual location is because I want to put a rear mounted winch behind the 4x4 Labs rear bumper (that will be coming soon hopefully!) and already have a Ramsey RE12000 all rebuilt and ready to be fitted up. No much room left with that monster under there.

So besides adding some weight(when its full) up high, is there any other drawback to an overhead tank I am missing here? No pump to worry about, piping is protected, won't rust up there, but a bit of a pain to fill? Anything else to consider before I start cutting?

 

[mct75]

The principle issue is a hellish death should be tank be damaged. I'd feel better with a fuel cell but even then, there is a reason fuel tanks are basically required to be inside the frame and between the axles of a vehicle.

 

[N22]

Great fire hazard in a rollover.
More chance for said rollover with fuel sloshing around at a higher CG.

The dynamic force of the fuel at about 6lbs per gal. with the leverage from being up so high...... 1/2 tank would be around 63lbs about 6-7ft above the center of rotation......plus the force of the 63lbs of fuel moving from one side of the tank to the other......
A few deg of body roll would put that weight out past the tires....
Or something like that.

 

[MoJ]

Please don't.

 

[AppleTech]

Yeah don't do it, plain and simple.

 

[DirtScaresMe]

In general it seems like a bad idea, but no one would give a second glance to fuel cans on the back or even on the roof (minus the higher weight thing). I guess I'll ask the forum here why I'd get dumped on if I asked to put a plastic fuel tank strapped to my rear swing arms, but if I put roto tanks back there it would be expedition-y.

 

[mudgudgeon]

lol @DirtScaresMe


It certainly wouldn't be my first choice.
I think you'd get a lot more vapourising of the fuel due to the tank being out in the sun. Tank would need to be well vented. When empty, you'll have a tank full of vapour for some time after its completely drained too.
I'd want the tank to be well baffled to stop fuel sloshing around. A single large tank will be more of a problem than several smaller jerrys in terms of weight shifting due to fueling sloshing to one side through cornering forces.

can you have the tank modified to leave provision for a winch install and fit it under the rear floor?

 

[LandCruiserPhil]

This is wrong on so many levels.

 

[Red Merle]

This is one of those times where I question the notion that there is "no such thing as a dumb question". Sorry man, this is just a non starter for a number of reasons. So many ways that this could result in a rolling fireball that endangers not only the people in the truck, but any poor sap that happened to be sharing the road with them when things go off the rails.

Just put it where the spare tire is like a normal person.

 

[artech]

But having gas cans or even propane tanks on a rear swingout where they can be crushed in a statistically far more common traffic accident is somehow OK? WTF people!

In general it seems like a bad idea, but no one would give a second glance to fuel cans on the back or even on the roof (minus the higher weight thing). I guess I'll ask the forum here why I'd get dumped on if I asked to put a plastic fuel tank strapped to my rear swing arms, but if I put roto tanks back there it would be expedition-y.

Yup, just like the poor saps driving a Ford Pinto back in the day. I would never put a pile of explosives between me and the idiots tailgating me while texting, eating a bowl of cereal, and taking selfies of their morning commute, but a lot of people do. Makes me shudder every time I see a rig like that, it feels like wearing semtex instead of plates in a bulletproof vest. But, different stroke for different folks and all that, and I'm not crapping all over them for doing it. It is, after all, so very conventional.

lol @DirtScaresMe
It certainly wouldn't be my first choice.
I think you'd get a lot more vapourising of the fuel due to the tank being out in the sun. Tank would need to be well vented. When empty, you'll have a tank full of vapour for some time after its completely drained too.
I'd want the tank to be well baffled to stop fuel sloshing around. A single large tank will be more of a problem than several smaller jerrys in terms of weight shifting due to fueling sloshing to one side through cornering forces.

can you have the tank modified to leave provision for a winch install and fit it under the rear floor?

Thank you for seeing my point. It's really not my first choice either, but I'm considering it as an option. No way to do both in the space available underneath and have much tank capacity left, the gearbox on the big Ramsey makes that impossible. I don't believe that a winch ARB front will take this winch either, the mounting is different than on most winches, it's more like the industrial hydraulic winches on flatbed wreckers. I might just need a different winch. And a different bumper, since my ARB is a non-winch model.

I had not thought about the vaporization from the sun, and that might be a factor with sizing the tank vent. I figured that the tank would either be full or empty during use and it is baffled for marine use, so was not too worried about slosh. The tank is from a reputable maritime company and tested to USCG standards which obviously are not DOT standards but it is not some slapped together hack job or plastic hardware store gas can.

Asking about technical problems here folks. The total weight is 132 pounds of fuel plus the tank, sender, hardware, and lines-about 25 pounds. So much less than some of the RTT's out there. Centered on the long axis means it extends 8 inches either side of the centerline and 7 inches high. The weight would be centered and very stable. My 85 pound spare is already up there all the time, no issues. I've had several hundred pounds of lumber and plywood up there in the past, no issues. My truck is not lifted and has 265 tires, or I wouldn't even consider putting more weight up high. Still has the sway bars and the factory suspension. The 200 pounds of winch and crossmembers, and 250 pound rear bumper that are being installed concurrently with the tank should reinforce the stability triangle enough to keep everything in balance.

Ever ride in a Cessna? The fuel tank is right over the cockpit at the wing root, and that passes FAA standards which are far tougher than DOT ones. Of course, aircraft don't get rear-ended at stoplights very often. Just some food for thought.

 

[mct75]

You've obviously already made up your mind, so I am not sure why you even bothered asking us.

 

[artech]

No just trying to explore some more uncommon options to fuel storage. An inside fuel cell might work if I had drawers, but I use my 3rd row seats quite often. I'm not a fan of bumper storage myself, and the underside real estate is becoming packed full, so trying to figure something else out. What else is left?

 

[mct75]

A MAF long range tank holds 38 gallons and replaces the stock tank.

If you relent to only using the tank off-road and only when required I guess it is not the worst idea out there. I would still do a fuel cell as the last thing you want is gasoline filling the passenger compartment.

 

[artech]

I agree completely.

 

[scottryana]

There are some really strong ideas with regard to fuel tanks. I know when I was thinking about doing a gravity feed secondary tank to the main tank people were going to lynch me. There are many fuel connections on the truck but that one that I was thinking about was a nun killer. I get it fuel is bad. But jerry cans on the roof, jerry cans hanging off the back waiting to be rear ended, etc. We all have to use our senses and deal with what is an acceptable level of risk. I have even used the 4x4labs interior cargo jerry can holder for fuel before, but that was only while offroad and I was fairly certain the level of risk was very low.

If you have weighed out all your options, considered all the safety risks and it is acceptable to you, just make sure you are as safe as your "plans" are.

 

[mct75]

Here is where I got lynched, for the record:

Passive fuel subtank?

 

[artech]

Yup, fuel is an emotional issue and I get that; the fear of burning is centered deep in the hindbrain and goes way, way back. We deal with fuel spills every day in public safety so maybe I have a different perspective than most folks, but some of the storage options are simply inherently safer than others. Inside the frame rails is without a doubt the best option, no question there. That's the best protection for the tank in an accident hands down.

To my trained eye the bumper storage of fuel cans is so very unsafe that it makes me cringe, but most folks don't give it a second thought. The one saving grace of most of these mounts is that the cans are usually empty when they get crushed in an accident, because why have a bunch of old gas in the tanks when you don't really need it? Most folks just fill them when going out on a long trip which is not that often. The full ones spray everywhere in a spectacular fashion when crushed and are simply incredibly dangerous. I would not have them on my rig.

A properly constructed and properly mounted fuel cell inside the vehicle is probably the second best choice, mostly due to the engineering that goes into protecting the passenger compartment. These tanks can be had with foam fill and multiple safety systems in the race-ready models and while a passenger compartment full of fuel vapor would be very, very bad, it would be much less likely to occur in an accident.

I'm not really gonna mention plastic hardware store gas cans here because those are not really storage, more like transport tanks from the gas station to the garage. I do see them being lugged on the roof racks or in open pickup beds and it always makes me wince, but it's no different than when I go over to get gas for the lawn mower. Zero protection in those and sure recipe for disaster in an accident, but thousands of gallons are moved every day in just that fashion, mostly without incident. I do drive like a granny when I'm hauling in that fashion though.

Roof mounted tanks are prevalent in tail-dragging aircraft and for good reason. The fuel pump has a fail-safe and can still use gravity to feed the engine if the pump quits. Of course, you can't just 'pull over and stop' when flying, and you won't go very far without a fuel pump, but the idea is to allow the plane to get back on the ground safely. And there are aircraft related valves and fittings to allow safe connections for these overhead tank applications. So not as unsafe as it initially appears, though certainly not the best choice for ground vehicles. It is NOT like hauling plastic gas cans around bungee corded to the roof rack.

Just trying to explore some less conventional options and see what else anyone can come up with. I'm hoping someone has an alternative method or deciding factor that I have not considered. Lynching aside, when the emotion is separated out some people do bring up good points and that's what I'm hoping for here.

 

[stock]

People drive with Jerry can's up top. What's the difference? Heck, many on here have Jerry's on their rear swing outs. You are much more likely to get rear ended than roll.

 

[LS1FJ40]

I won't address the safety issue because as others mentioned you have to determine your needs and safety.

What I wonder is, where are you going that you need the additional fuel? Or is it more a convenience thing that you just want to fill up once a month or something? Is this something that will be up there all of the time but only filled when you are going somewhere where you may need the additional range?

I can see this being useful as a "I'm going to be away from fuel for the next 7-10 days, exploring Moab and don't want to worry about fuel" yet not filling it when driving around town. I personally wouldn't want the extra weight always up there. I carry a single jerry can, with 2-3 gallons in it, on my roof rack all of the time (more for others than myself). (When full it can vent off and leak a little so I just leave some room). When I go out somewhere I carry two full cans. They will get moved to my rear swingout as soon as it arrives.

Good luck, I look forward to seeing what you come up with.

 

[bloc]

The difference with Jerry cans up top is you drain them individually, so while there is additional weight up high, if any of it is sloshing it is substantially less than 5gallons. Also, MFCs at least are extremely durable. Depending on the speed of the roll I could see them surviving intact. I can't say the same about any kind of fuel cell or tank that would be big enough for what OP is asking.

That said.. having rolled one rig I'm not putting jerries up top either. My plan is to build a swing-down tray that puts two in the spot vacated by the factory spare tire. Only 10 gallons, but as safe as possible and the least likely place to impact vehicle handling.