Odd shaped gas tank = inaccurate gauge Pics incl.

[bsutravis]

Got an odd question. This was my Grandfather's boat and now it's mine..... from the date it was new the fuel gauge never was accurate but Gramps just carried a small gas can w/ him in case he ran it out. Now that it's mine I'm trying to fix the issue.

After pulling back the carpet and revealing the hidden portion of the tank I discover that the vast majority of the tank is only 4" deep, while the end that contains the fuel level sending unit is 9" deep. With this shape, I can't see how a standard float can keep any sort of accurate fuel level on the gauge.

Does anyone have any ideas how to solve this problem?

 

[tpenfield]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

Was the carpet laying directly over the tank? If so, that should be corrected.

Based on the fuel gauge reading, that second half of the tank must seem like it lasts forever. Not much you can do with only 4 inches of space for the float reading. The accuracy must be fairly bad.

However, the only safe place for the sender is at the top of the tank. There might be a sender for such a tank that has a non-linear output

 

[bsutravis]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

Was the carpet laying directly over the tank? If so, that should be corrected

No, there was a piece of marine grade plywood over the tank that the carpet was over.....

Seems like a crappy design for the fuel tank. I'm gonna take the sending unit off later and see if there's anyway to bend the float wire so it gets a little more accurate.

 

[Home Cookin']

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

I have a flat tank like that but not with the tower. Guages are never accurate--in any boat. You have to get to know yours. Fro example, mine stays "full" until I have a 1/4 tank then it says "1/2" and when it says "1/4" head for shore! So I ue it like the warning light on a car.

 

[oops!]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

i would rotate that panel were the sender is......have the sender at one side,,,,,,then when the float goes up.....it will travel freely.

you will need to know.....that when the boat says 1/2 a tank.....that you are in the area where the majority of the fuel is.

when it says 1/4 tank.....you still have lots to go.

and when it says empty......you are really empty

the good thing is you can monitor the float position in relation with the fuel level after seeing it, and know what the sender is telling you

 

[Silvertip]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

The common misconception is that a fuel gauge reading MUST change at a linear rate since that's how the gauge is calibrated. Obiously the vast majority of recreational boat fuel tanks are not perfectly square, round, or rectangular so a float mechanism cannot possibly read in linear fashion. It does however read fuel LEVEL. Now here is the rub. When the gauge reads 1/2, the tank may or may not be anywhere near half full. So -- since you tend to fill the tank before a trip, you then know the tank is full so having the gauge read FULL is of little importance. But you do want to know it is accurate when it reads EMPTY. So the trick is to adjust the float arm to read accurately when the tank is empty. You may even adjust the arm so that it provides a couple of gallon cushion just in case youa re not paying attention. To comprehend how this works, think of a cone shaped cup. Draw a line at the 1/2 point. Now you should be able to immediately see that the bottom half of the cup holds far less liquid than the top half. Yet a fuel sender would show you had 1/2 tank of fuel. Yes -- the LEVEL is at the half way mark but the VOLUME is at the 1/3 REMAINING point. The point of all this is that you cannot make the gauge dead accudrate at empty, 1/2 and full. You can make it fairly accurate at any one of the three points but not all three.

 

[oops!]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

good one tip

 

[bsutravis]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

Thanks for the replies fellas...... Good analogy with the cup! I'll play with the float to make it correct at Empy and figure out where my guage reads everywhere else in relation to how much gas is in the tank.

Thanks!

 

[Mikeyboy]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

That is a great explanation silver tip.

 

[Beefer]

Re: Odd shaped gas tank = inaccurate gauge Pics incl.

There is one other option (maybe 2) to 'correct' this so that even in the most bizarre shaped tanks you can gt an accurate reading. It's a fuel gauge made by a company called CruzePro out of New Zealand (anyone know why Chrome spell-check says that's spelled incorrectly?). I have one, and you fill the tank in increments of 1/16 of the tank's capacity. It then reads what the sending unit is sending back at each increment, and gives the correct read out. I have one, and as soon as I can afford to fill up my tank (80 gals x $4.29 = too expensive), I'm going to set it.

You can read all about it here; http://www.cruzpro.co.nz