Thread: New project - Diesel tank

I am looking at making a diesel tank for under the tray of my Iveco 50c18. I currently uses a 200L roto moulded plastic fuel tank mounted on the tray. While it has been great on long trips, it's a pain in the ar.. to remove & refit when home when I want to use the full tray.
I have a space under the tray 2400 x 650 x170 where I can mount a tank permanently. I could make a rectangular tank 2000 x 640 x 160 to fit in this space which will give me around the 200L. My question for you guys who know your metals, what is the ideal metal & gauge to make it from. If I construct it to the size mentioned, I could use 2 x 2400 x 1200 sheets for the job which would include 2 baffles & 2 end caps. For this project I would use the services of a m8 to tig the seems as I don't have TIG experience yet.

Originally Posted by jex

I am looking at making a diesel tank for under the tray of my Iveco 50c18. I currently uses a 200L roto moulded plastic fuel tank mounted on the tray. While it has been great on long trips, it's a pain in the ar.. to remove & refit when home when I want to use the full tray.
I have a space under the tray 2400 x 650 x170 where I can mount a tank permanently. I could make a rectangular tank 2000 x 640 x 160 to fit in this space which will give me around the 200L. My question for you guys who know your metals, what is the ideal metal & gauge to make it from. If I construct it to the size mentioned, I could use 2 x 2400 x 1200 sheets for the job which would include 2 baffles & 2 end caps. For this project I would use the services of a m8 to tig the seems as I don't have TIG experience yet.

I've heard (but don't know for sure) that some stainless steels have issues, particularly for long tanks like yours, where sloshing fuel hits the baffles and can work harden them over time, eventually leading to failure of the baffles and cracks in the tank itself. Don't know anything about it, but worth looking into. More baffles maybe?
I was thinking that 170mm isn't very high, so you might not be able to access a lot of the capacity and if you have a fuel level sensor, it's likely to not be very accurate. What's the plan? gravity drain to your main tank? separate offtake? pump over system?
Cheers
- Mick

Hi Mick, Hopefully someone on this forum will know more about the SS issue you mentioned. With my truck, the only way you can use an auxilliary tank is to transfer the fuel from aux to main when the engine is off so the fuel gauge does not get confused. Therefore I don't need any sensors or gauges. With it under the tray, gravity feed would be slow. I currently use a CAT filter with a built in pump to transfer the fuel. The current aux tank line is plumbed into the breather hose.This set up works well but I would like to get the tank out of the tray. There are a few places along it's length where I could add a dip in the tank to get all the fuel out if required.
SS is what I was thinking of using but I am not sure which grade & gauge .
John

Sounds logical... I was think of some sort of automatic system, but that's over complicating it.
I figure that if work hardening of the baffles was an issue, then boat fuel tanks would have the same problem. A quick google search indicated that 316 stainless between 1.6 and 3mm was pretty common. The long range tank in my 4WD is 2mm aluminised mild steel. The tank in my boat is 3mm aluminium (not sure of grade).
Good luck with it.
- Mick

Yeah KISS is the go.
Is there any disadvantages with using aluminised mild steel other than rust ? The material would be cheaper and it would be easier to weld I would think. A good paint job would protect the outside from rust but the cost of painting might bring the cost back to stainless prices ?? I am not sure as I have not priced either material yet . Ally would be lighter but not sure of its durability on our rubbish roads.

John

I used to manufacture fuel tanks for 4WDs, and would suggest that 1.6 cold rolled sheet be used for the top while 2mm for the bottom, folded in a U, along the long edge, reason is that should it develop a leak, anyone, any where can weld it, if push came to shove, your own vehicle batteries will weld it.Black sheet steel can be used, but tends to flake off, creating problems, with filters, small hoses etc.
For the baffles I'd put them about 400 mm max. apart, folded on the four sides, at least a 25 mm lip, with the corners cut off 65 X 65 before folding, stagger the welds, so that the baffle is welded on both sides at least 40mm long each,to prevent localised stresses.
To weld the baffles on top I drilled 10 mm diam holes every 80 mm on the lid, like over sized spot welds. If you have to have a notch in it, to go around shocker or spring hanger, make sure that you have a baffle on that corner. I've repaired probably a dozen tanks that fatigued at that point.
Put your pick up pipes on top of the side of the tank, to prevent them getting broken off, 5/16" tube, (8mm) bent like a ? mark, I've found to be best, provided that it is secured to the sides by small tabs bent over to support the tube.
A good coat of primer and 2 coats of finish is all that is required. Don't make the tank mountings too rigid, as the flexing of the chassis at that length will cause problems. Stainless is a definite no no, as it work hardens with the flexing, OK in boats, as they are usually mounted low in the hull with very little, if any flexing.
I built a tank for my Suzuki Sierra tray top, 120 litres with an inbuilt 20 litre reserve that went up and over each side of the tail shaft. 150K not a problem with it, Anne Beadell Highway twice, Tanami Track 3 times, out to Gove, into the Bungle Ranges, some real rough tracks there.
Kryn

Thanks Kryn, a lot of good tips in your post. I appreciate you guys taking the time to pass on your experience. Did you TIG or MIG your tanks ?
John

Originally Posted by jex

Thanks Kryn, a lot of good tips in your post. I appreciate you guys taking the time to pass on your experience. Did you TIG or MIG your tanks ?
John

Hi John,
Just passing on my experience and tips, I'd picked up over the years. My tanks were MIG welded and tested to about 20 PSI, with soapy water in a spray bottle. I did have one tank that leaked, nowhere near the welds, turns out the sheet was porous, black steel by the way.
That's the beauty of this forum, members are freely giving information, advice, some times even stuff that you are chasing or no longer required.
If you have anymore questions, please feel free to ask on here or PM me.
Regards
Kryn

Watch the design of your ends too. On place I worked had some Al tanks made up for vehicles and they failed because although the ends were dished, they were dished into the tank. A bit of slosh and the ends would push out, effectively peeling the welds apart. The dish should have been sticking out so that the welds were only ever in tension.
I'd be tempted (if it was me doing this - never done it before though) to fold up some end pieces such that the join between the end and the long sides/ base was say 25 to 50mm back from the folded corner. That way the weld would not be flexed when fuel pushed against the ends.

Just a thought
Michael

Because of the size of the tank H X W, I don't think it would be a problem with the amount of baffles I'm suggesting. If you did want to go with Michaels suggestion, I'd put the folded edge to the inside and about 5 mm proud, when welded will give a nice rounded finish. Putting the folded edge on the inside, I've found, creates the problem of welding the inside corners, unless they are welded on the outside prior to welding in place, the finish would be similar to a jerry can for fuel. My tanks were all butt jointed.
Kryn

Originally Posted by KBs PensNmore

Putting the folded edge on the inside, I've found, creates the problem of welding the inside corners, unless they are welded on the outside prior to welding in place.

Sorry - incomplete explanation on my part. Yes, I did mean for the corners on the ends to be welded prior to welding in place.

Michael

I operated truck fleets for many years so I can perhaps add some suggestions from that perspective. Given your intended tank measurements, are you mounting the tank along one chassis rail or transverse under both rails? If transverse, you need to be mindful of chassis flex in your tank mountings. On one of my first trucks, my boss fabricated a large rectangular steel tank bolted hard up to both chassis rails. Chassis flex caused the tank to continually leak on external seams, which he used to arc weld while we extinguished the flames. Long copper fuel pickup lines in diesel tanks tend to work harden over time and if there’s a lot of sloshing, can crack (frustrating because you can’t initially locate where it’s sucking air). Tank baffles often need some strength against the fuel slosh across the tank (espec if it’s 2m long & 200 litres can exert considerable pressure). Tank baffles are frequently dished for additional strength but Kryn’s suggested 400mm spacing would alleviate this. In the 1980s, new ADR design rules required truck fuel tanks to survive a drop test and to have recessed filler caps (in case of accidents). Perhaps other forumites could comment as to whether this applies to smaller vehicles (Kryn, when you manufactured 4WD tanks, did the design require approval?) Anyway, hope this helps. Peter

Originally Posted by peterbilt

I operated truck fleets for many years so I can perhaps add some suggestions from that perspective. Given your intended tank measurements, are you mounting the tank along one chassis rail or transverse under both rails? If transverse, you need to be mindful of chassis flex in your tank mountings. On one of my first trucks, my boss fabricated a large rectangular steel tank bolted hard up to both chassis rails. Chassis flex caused the tank to continually leak on external seams, which he used to arc weld while we extinguished the flames. Long copper fuel pickup lines in diesel tanks tend to work harden over time and if there’s a lot of sloshing, can crack (frustrating because you can’t initially locate where it’s sucking air). Tank baffles often need some strength against the fuel slosh across the tank (espec if it’s 2m long & 200 litres can exert considerable pressure). Tank baffles are frequently dished for additional strength but Kryn’s suggested 400mm spacing would alleviate this. In the 1980s, new ADR design rules required truck fuel tanks to survive a drop test and to have recessed filler caps (in case of accidents). Perhaps other forumites could comment as to whether this applies to smaller vehicles (Kryn, when you manufactured 4WD tanks, did the design require approval?) Anyway, hope this helps. Peter

Hi Peter, this was about 1980 - 2000 that I did tanks, they didn't require approval. I built several at 200 litres for generating and pumping plants for several Govt. departments, and one for a Sierra long wheel base Suzuki that went into a Sierra tray top. I used to make them for other Adelaide 4WD outlets also, so they couldn't have been tooo bad.
Kryn

Originally Posted by peterbilt

In the 1980s, new ADR design rules required truck fuel tanks to survive a drop test and to have recessed filler caps (in case of accidents). Perhaps other forumites could comment as to whether this applies to smaller vehicles (Kryn, when you manufactured 4WD tanks, did the design require approval?) Anyway, hope this helps. Peter

Interesting. Not too sure if the recessed filler cap idea actually became law as I cannot think of a single manufacturer who does that off the top of my head. Another point that comes to mind is that at least one truck manufacturer uses fuel tanks with no baffles whatsoever, which does remove any chance of the baffle cracking I guess, although I would not build a tank without baffles personally.
My experience of truck fuel tanks tells me that there is only one way to weld a baffle in and that is to fully weld the baffle rather than stitch them in as the stitch welded baffles invariably fail. Kryn's method of welding either side with interlocking stitches is fine too.
Baffles need shape in them to prevent cracking, either a decent dish or a cross break is fine. On round tanks, my favourite method was to press a Mercedes Benz star in the baffle before welding it in. If a baffle or tank end can move, it will break, so you must always ensure that there is sufficient tension in the baffle or end.
When pressure testing a tank, 2 or 3 psi is more than adequate. Greater than this can and probably will lead to deformation of flat panel tanks, even explosion.
Do not solid mount a long tank such as discussed in this thread. Tank straps, shielded with rubber are a far better option as they allow flex without stressing the tank. Long flat tanks such as this demand two breathers as single breather tanks of this type are liable to spew diesel out the breather on a hot day as things expand. Your two breathers can connect together, but must be placed at opposing ends of the tank to allow for either a downhill or uphill attitude of the vehicle.
Stainless can be used quite safely and effectively for a tank as long as its work hardening properties are accounted for, (this means providing sufficient shape in ends and baffles to prevent movement), however Stainless does bring with it more cost and more specialised welding processes. Much the same applies to Aluminium, although it does provide a weight saving and less corrosion issues.
Whatever material is decided upon, I highly recommend providing a drain bung of some sort as apart from draining the tank, it allows for the bleeding off of water produced by condensation that infrequently filled tanks can produce.

I guess I should have googled fuel tank ADRs rather than relying on memory. ADR 17 was introduced in 1984 but only applied to commercial vehicles > 4.5T. https://www.infrastructure.gov.au/ro...f/vsb_06_m.pdf However it was repealed in 2005 and not replaced: http://www.fullyloaded.com.au/indust...e-resurrection Petrol engines and shonky fuel tanks (e.g.44 gal drums) once abounded in the transport industry but have fortunately disappeared. A drain plug for condensation is worthwhile but for common rail, high pressure diesel injection systems, an additional water filter in the fuel line is highly recommended. They’re quite cheap and can save thousands in repair/rebuild costs. Good luck with your tank fabrication; you should be able to build a good one with confidence.