1 Feb

Over the last week or so, “tank V2.0” was fabricated.

Reasons to redo the tank include: wanting to run ethanol, an incompatible fuel level sensor, an incompatible external fuel pump, the new ethanol pump is in-tank only, and the fuel tank sealant swells when exposed to ethanol. More subjective was that tank V1.0 had several weeping leaks, never enough to drip, but an annoyance. Also, the tank had warped badly during welding, something that only bothered me, but just knowing that it’s there, saying “you can do better” helped me decide to just that.

The pictures pretty much spell out how it went together. I splurged and went for “real” fuel tank doors just to see what you get. These are the low-end units (“only” $30 each!). They reminded me a lot of the covers on outdoor electrical outlets – in fact I wonder if those could have been used instead, except anything aluminum is a no-no for ethanol.

The layout’s pretty obvious, the dividers doing double duty of keeping the fuel load from sloshing side-to-side, and guiding it into the accumulator. The forward section of the tank makes due with one fuel door, such that if there’s cornering with any acceleration, the fuel will always enter the accumulator.

As can be seen, the water jet parts came out really nice – they provide a nice finishing touch to the tank plus providing a truly flat surface for the gasket to seat against.

The Walbro “E85 400 LPH” pump is only available as an in-tank unit, necessitating a mount, hose, and power, with everything sealed to keep fuel from leaking up past the threaded fittings. Stat-o-seals were used on the larger fittings and Honda-Bond gasket sealant was dabbed onto the screw threads. The fuel fittings shown are -8 for fuel supply, -6 fuel return, -3 vent, and a -8 fuel vapor return which vents vapor to the top of the filler hose. This was added because tank V1.0 constantly caused gas station fuel nozzles to trip off – very annoying. The idea is that fuel vapor flows up the vent hose to above the nozzle instead of causing vapor to rush back up against the incoming fuel, causing it to splash on the trip mechanism on the filler nozzle.

The 45-degree red and blue fitting that doesn’t go anywhere near the pump is actually the fuel return. Without it, returning fuel would drop all the way to the bottom of the accumulator, introducing air bubbles into the fuel right near the fuel pump inlet. The 45 degree coupler points the fuel at the wall of the tank so that it smoothly runs down the side – or that’s the idea.

The sheet metal shop was unable to close the sheet, meaning three long weld seams. Fearing the extreme warping that happened with tank V1.0, it was welded in 1″ increments, moving back and forth, side to side, and was rewarded with virtually no warping. Seen in the pictures below is the comparison of the tanks V1.0 and V2.0. Tank V1.0 warped, bending the top 4″ section of 0.065″ stainless on edge nearly 1.5″ over 44″. I can hardly imagine the enormous force needed to bend a 4″ thick section of stainless! Tank V2.0 shows practically no warping at all – very happy about that.

The last picture is a GM flex-fuel sensor. It’s a pretty cool device that outputs a duty cycle measuring the exact amount of ethanol in the fuel, while the frequency measures fuel temperature. Knowing the ethanol content of the fuel allows the ECU to adjust timing, fuel, and boost instantaneously. The sensor gets plumbed into the fuel return line and while the ports are fairly small, reader “JR” recommended running fuel through the sensor, but also around it, so that 80% of the fuel takes the easy way around while 20% actually flows through the sensor.

If there’s ever a tank V3.0, the dividers will be welded to both the top and bottom skins, like tank V1.0 was. The need for this was made clear during leak testing where the tank was pressurized, with a distinct “Bong” and seeing the sides of the tank physically balloon slightly. Speaking of leak testing, yes there were leaks, but not as many as before. Also, this time I put on my old-man glasses, really strong reading glasses which allow me to get about 2″ away from the welds. Between that and a flashlight, questionable spots were touched up, while soapy water handled finding all the obvious leaks. While the tank was leak-checked three times, I admit that I wonder if it’s still going to leak. I suppose I could fill it with water and let it sit, but I think air is more able to get through really small holes than water is. Someone suggested pressurizing the tank and seeing if it holds pressure. Yes, but if the pressure drops, then what? So there’s a leak, but how can it be found? Soapy water and air pressure, so that’s what I went with right from the start.