the fuel qty problem

[aido]

i recently got a new underfloor 130 ltr tank made.
silly me forget to order a tank sender hole cut at the top.
just made it like the old one, ie no quantity indication.



after a battle fitting the tank, i then realised i really need to know if its getting low. hate to run out of gas.

so what to do?, seeing my motor is not rebuilt yet and i've plenty of time to fiddle, i decided to build a minature magnet float system due to it's intrinsic safety, that is no wiring is inside the tank. simple in theory also, minature reed switchs and some brass work.

the system had to be small enough to fit down the aft tank breather right angle fitting, which normally is about
10mm diameter. after making several float styles, i found 5 thou brass shim material could not remain bouyant in fuel at a float diameter of 10mm. oops, got one made out of paper and superglue for sealing (also 3m fuel proof coating) which could easily support a small magnet and proof of concept it worked. so then settled on an aluminium tape rolled into a cylinder with epoxy endcaps.
this is still loating in a sample of fuel after a week and is the final float i will use for now.

to save time at this stage, i've settled for a system capable of 5 level resolution. ie, full, 75%, 50%, 25% and zilch + about 10 lts. here's the final design ready to fit in the tank, temporary led's were used for bench, or should i say, table testing.



sorry for the low res pics,
and the longwinded story.
maybe someone else could use a setup like this.
the other option was a capacitance system using concentric brass tubes, say 8mm inside a 10mm tube.
this is a continuous level system, (no level steps) but does
involve a voltage in the tank, that's why i did not continue
with it. though it did work really well when using a cheap
digital meter on the capacitance scale. reading went from 50 to 100 smooth as silk when lowered into fuel.
might get back to that one later.

[Kerry]

I use a stick

Cheers, Kerry.

[peterbo3]

Aido,
I am with Kerry 400%. Fuel sender setups are TOTALLY unreliable!!!
Suggestion:
1.Cut hole in top of tank in a position where you can cut a hole for a screw-in inspection port in the deck above.
2.Fit an approved marine grade fuel cap to the tank.
3.Obtain a non conductive (ie-no static charge transfer) dipstick (wood is good ) & calibrate same by manually filling tank with water in 20 litre increments & marking the dipstick level after each increment. Notch the dipstick
with a file or saw to ensure that marks are permanant.
4.Once that is complete, empty tank of water & put in one litre of metho. Shake tank, drain residue & you're ready to go. The metho will combine with any remaining water & will assist in getting all water out.
Fuel senders tend to stick or short out & are never reliable. Dipstick gives you a true reading & even if the boat is rocking you can see how much fuel is sloshing around in the tank.

[FLATHEAD1]

I was going to suggest why not use a fuel flow meter option and connect to the sounder/gps but I like the stick idea better.

I have continual problems trying to get a good seal where the sender has been cut into the top of the tank.

FLATHEAD1

[Big_Kev]

I used to run a fuel gauge in the half cab that I had and it was fxxxing hopeless.
The trusty old stick method was the go for sure.
The new boat has the stick type fuel gauge which also doubles as a prop to hold the floor open when filling the tank.
But at least the LED's will give you some sort of an idea.
Cheers Kev

[T-REX]

The deck fill option is the way to go and this can also be used to add fuel in rough conditions if required. Stick with the Dip Stick and make two.
Cheers.

[aido]

thanks for the ideas guys,
dipstick must be the most accurate way to go
and is always going to work.
i've fitted the 4 led indication system anyhow cause it was
ready to fit, after much rooting around. should be convenient and an entirely repeatable qty display.
lets see if i'm still happy with it down the track.
i'm still going to have a dipstick on hand like you all
recommend.
flathead, fuel flow metering was my first plan and got all excited about the navman f2100 system for $300. went off the idea recently though when the mechanics at cbs advised against fitting one to a large motor >200hp. although unable to verify it, they suspect it caused a fuel supply restriction which cooked a couple of 225 efi motors recently.
thanks again.
aido.

[nofrills]

mate, stick a four stroke yamaha on the back. By the time you burn the 130lt of fuel you will be in so much trouble with the boss you would'nt want to come in.
cheers.

[aido]

might end up doing that if cbs keeps dicking around putting my suzi 200 efi
back together. already 4 weeks of no go...
they're starting to pi$$ me off no end.

[Volvo]

Ill second the dipstick method lol. Say anyone know if they make them rubber fuel bags(for the luv of me cant remember their name lol) for carrying extra fuel??.
Cheers
PS forgot ta say "For Petrol"
just remembered............Bladders .

[peterbo3]

Volvo,
They still make 'em. Try Glascraft in Brisbane.