Aux fuel tank weight distribution

gearhead · 02-01-2021, 09:33 AM

To those that have an auxiliary fuel tank in their truck bed, how did the added weight of the filled tank get distributed front axle vs. rear axle?

Javi · 02-01-2021, 09:58 AM

Quote:

Originally Posted by gearhead

To those that have an auxiliary fuel tank in their truck bed, how did the added weight of the filled tank get distributed front axle vs. rear axle?

Boy, that's going to be subjective... on mine the tank is only 20" deep but tall and long.. so it sits a loooong way from the rear axle..

gearhead · 02-01-2021, 10:06 AM

Quote:

Originally Posted by Javi

Boy, that's going to be subjective... on mine the tank is only 20" deep but tall and long.. so it sits a loooong way from the rear axle..

Yes I was thinking yours would be a bit different. The one I've been eyeing is 20" deep and 19" tall, 60 gallon.
IF I sell the Bigfoot.

notanlines · 02-01-2021, 10:11 AM

Ours when full of diesel puts about 250 pounds on the rear axle and 150 up front.

**JRTJH** · 02-01-2021, 10:28 AM

From an airplane loading perspective, the formula goes something like this:

Measure the centerline of the rear axle to centerline of the front axle. Then measure from the centerline of each to the centerline of the tank. Divide each measurement by the total measurement. That will give you an APPROXIMATE percentage of the added weight that will be placed on each.

If the CL tank were 1/3 of the distance to the CL rear axle and 2/3 of the distance to the CL front axle, You'll end up with something like, 66% on the rear axle and 33% on the front axle. As an example, if the CL front to CL rear is 90" and the CL tank is 30" to the CL rear and 60" to the CL front, then the calculations would be 30/90=0.33 and 60/90=0.66 So, 33% of the tank weight would be on the front axle and 66% of the tank weight would be on the rear axle. Yes, somewhere in the calculations, you have to "reverse the data"... Now it should be "clear as mud"....

Granted, there are things like height of the tank, slope of a front/rear wall of the tank, etc that will affect the "base computations" but they will "minimally affect the general outcome".

On airplanes, things like front strut pressure and air density/temperature affect rotational speeds, but there's no need to try to make "weight transfer in a stationary tank" that difficult.

xrated · 02-01-2021, 11:24 AM

And then, there is this one. I just bought this one to replace an old 42 gallon steel tank. This one is 60 gallon and only 16 1/2" tall at the top of the tank, so below the top of the bed rails. And the "L" shaped area is low enough that my crossbed Toolbox will sit right over the top of the horizontal area of the tank. I don't know how you would calculate the weight distribution with this.....but then again, I really don't care with having a Dually.

**JRTJH** · 02-01-2021, 11:35 AM

Quote:

Originally Posted by xrated

And then, there is this one. I just bought this one to replace an old 42 gallon steel tank. This one is 60 gallon and only 16 1/2" tall at the top of the tank, so below the top of the bed rails. And the "L" shaped area is low enough that my crossbed Toolbox will sit right over the top of the horizontal area of the tank. I don't know how you would calculate the weight distribution with this.....but then again, I really don't care with having a Dually.

Yep, It wouldn't be as easy as "one set of calculations" since the tank centerline will be constantly changing as the vertical part of the tank drains. The CL will "constantly moving rearward" as the vertical part empties... But, from a general approach for "duct tape and bailing wire approximations", I'd take a "best guess" on where the CL is located and just do one calculation without making it any more complicated than needed for "bailing wire".....

Javi · 02-01-2021, 01:26 PM

Here's mine...

gearhead · 02-01-2021, 02:28 PM

Quote:

Originally Posted by notanlines

Ours when full of diesel puts about 250 pounds on the rear axle and 150 up front.

^That's plenty good. I just want some on the front.

roadglide · 02-01-2021, 03:51 PM

Quote:

Originally Posted by notanlines

Ours when full of diesel puts about 250 pounds on the rear axle and 150 up front.

As I remember you have a long bed. I think a shorter bed lengths would put more weight on the axels.

jasin1 · 02-01-2021, 05:12 PM

How are you guys transferring the fuel? Drip flow into tank filler? Or separate pump and handle?.. I’m also thinking of filling a swimming pool up with diesel while prices are low

Javi · 02-01-2021, 05:44 PM

Gravity feed, works great.

jasin1 · 02-01-2021, 05:47 PM

Quote:

Originally Posted by Javi

Gravity feed, works great.

Ok thanks. I’m probably going to get a tank as well. Wasn’t an option when I was 1000 over gvwr

xrated · 02-01-2021, 06:51 PM

Quote:

Originally Posted by jasin1

How are you guys transferring the fuel? Drip flow into tank filler? Or separate pump and handle?.. I’m also thinking of filling a swimming pool up with diesel while prices are low

I'm doing both....gravity and a fuel pump. Overkill? Well, maybe...but since this tank is a replacement tank for the one that was in my truck that had a pump type transfer system, the wiring is already there and everything I need to install it. But I also want gravity flow for the longer trips and I bought the install kit to be able to do that.........so Both!

notanlines · 02-02-2021, 03:34 AM

Quote:

Originally Posted by jasin1

How are you guys transferring the fuel? Drip flow into tank filler? Or separate pump and handle?.. I’m also thinking of filling a swimming pool up with diesel while prices are low

I also use gravity setup and it has worked flawlessly for three trucks and both the trucks of friends that have installed the same setup.

jasin1 · 02-02-2021, 04:20 AM

I like the gravity setup but am a little Leary of drilling a hole in the fill tube. 2018-2020 Rams have the cp4 fuel injection pump and when it fails it sends shrapnel into the entire fuel delivery system.Ram sometimes replaces the entire system(super expensive) or tries to blame the owner saying bad fuel caused the problem. They may try and say metal from drilling or debris from aux tank is getting into the pump to deny warranty.It’s a known problem with cp4 pumps.Ram has since reverted back to the cp3 pump that it had for all the years prior and now for 2021 going forward.
It’s gonna be a pain but I may go with the tank/toolbox combo with a pump under the cover. I have a 50 gallon factory tank so that helps.I will just have to transfer fuel at rest stops.

xrated · 02-02-2021, 04:37 AM

Quote:

Originally Posted by jasin1

I like the gravity setup but am a little Leary of drilling a hole in the fill tube. 2018-2020 Rams have the cp4 fuel injection pump and when it fails it sends shrapnel into the entire fuel delivery system.Ram sometimes replaces the entire system(super expensive) or tries to blame the owner saying bad fuel caused the problem. They may try and say metal from drilling or debris from aux tank is getting into the pump to deny warranty.It’s a known problem with cp4 pumps.Ram has since reverted back to the cp3 pump that it had for all the years prior and now for 2021 going forward.
It’s gonna be a pain but I may go with the tank/toolbox combo with a pump under the cover. I have a 50 gallon factory tank so that helps.I will just have to transfer fuel at rest stops.

I'm not sure about the install kit for a Ram truck, because I have a Ford...but, you aren't drilling a hole in the filler neck. You cut out a section of the filler neck and install a metal pipe that has the fitting already installed in a bung fitting that is already welded to the metal pipe. If the filler neck is all metal (Ford is NOT), you simply remove it from the truck and do your cutting, then clean any and all shavings out of it, install the "T" piece and reinstall the fill tube. Zero chance of introducing any metal shavings into the fuel system...unless you just don't bother to clean everything up after making the cut. The Ford system uses a thick rubber tube for a fill neck but even at that, I will probably just remove the filler neck after taking my measurements, then do the splice, then reinstall. I am also going to add an inline filter in the hose that goes to the main tank from the aux. tank....plus the truck has two more fuel filter in the fuel pump circuit to the injector rails.
Here is a picture of the install kit for the Ford.....

jasin1 · 02-02-2021, 04:40 AM

Quote:

Originally Posted by xrated

I'm not sure about the install kit for a Ram truck, because I have a Ford...but, you aren't drilling a hole in the filler neck. You cut out a section of the filler neck and install a metal pipe that has the fitting already installed in a bung fitting that is already welded to the metal pipe. If the filler neck is all metal (Ford is NOT), you simply remove it from the truck and do your cutting, then clean any and all shavings out of it, install the "T" piece and reinstall the fill tube. Zero chance of introducing any metal shavings into the fuel system...unless you just don't bother to clean everything up after making the cut. The Ford system uses a thick rubber tube for a fill neck but even at that, I will probably just remove the filler neck after taking my measurements, then do the splice, then reinstall. I am also going to add an inline filter in the hose that goes to the main tank from the aux. tank....plus the truck has two more fuel filter in the fuel pump circuit to the injector rails.
Here is a picture of the install kit for the Ford.....

Well that makes sense. I don’t know where I saw you have to drill..maybe it was just one brand of tanks. I appreciate the update

xrated · 02-02-2021, 05:27 AM

Quote:

Originally Posted by jasin1

I like the gravity setup but am a little Leary of drilling a hole in the fill tube. 2018-2020 Rams have the cp4 fuel injection pump and when it fails it sends shrapnel into the entire fuel delivery system.Ram sometimes replaces the entire system(super expensive) or tries to blame the owner saying bad fuel caused the problem. They may try and say metal from drilling or debris from aux tank is getting into the pump to deny warranty.It’s a known problem with cp4 pumps.Ram has since reverted back to the cp3 pump that it had for all the years prior and now for 2021 going forward.
It’s gonna be a pain but I may go with the tank/toolbox combo with a pump under the cover. I have a 50 gallon factory tank so that helps.I will just have to transfer fuel at rest stops.

Quote:

Originally Posted by jasin1

Well that makes sense. I don’t know where I saw you have to drill..maybe it was just one brand of tanks. I appreciate the update

Don't feel bad, I thought the very same thing until I actually got serious about getting a new tank and trying to do the gravity feed thing.

jim1 · 02-02-2021, 07:44 AM

Hi I just wanted to let you know I was told to use Loctite 567 sealant with PTFE or something comparable on the diesel fuel tank and line fittings and no leaks. Do not use teflon tape the frayed pieces can come off and raise hell with you fuel system, pumps injectors etc. Also recommended for gas systems. Just a heads up. Good luck! I used a RDS fuel tank with the gravity feed and It works great.

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