Drain gas tank to tell where empty is.

Ifishmuskie2

Ifishmuskie2

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I ran my kicker that has a 12L tank until it ran out of gas. I then marked the tank with magic marker to tell where empty is. 6L of gas is about 15hrs trolling at 3mph. I wrote that on the tank too.
Now I’m wondering about the on board tank. The fuel gauge is not very accurate.
I’m thinking about draining it through the fuel line that goes to the engine. Then I’ll know where empty is. Then I’ll install a new bobber style sender and mark the gauge where empty is.
Any thoughts on this?
 
C

Chris1956

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Mar 25, 2004
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That should work. Using the fuel line to empty the tank will be a bit tricky as the tank level gets low. You might extend the fuel line and place the primer bulb at the far end of it, so you can get the siphon going, and then remove the bulb to allow faster flow. Alternatively, an electric fuel pump is less than $15 at amazon.


My fuel gauge read empty when the 18Gal tank is at 1/3, and each 3 gal of fuel changes the gauge by 1/4 tank. So 12 Gal is 1/2 tank, 15 gal is 3/4 tank etc. It is consistent.
 
alldodge

alldodge

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It should work but over time things still change. If your gauge sender was adjusted to show empty a little before it was kind of gives you a reserve sort of thing
 
C

Chris1956

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Gee, I'll bite. Other than splicing in a resistor, how does one adjust the fuel gauge?
 
Scott Danforth

Scott Danforth

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if its a float/rheostat sender, you simply bend the arm for adjustment

if its an ultrasonic sender (used on some new boats), you plug the laptop in and reprogram the sender.
 
Texasmark

Texasmark

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Chris1956 said:
That should work. Using the fuel line to empty the tank will be a bit tricky as the tank level gets low. You might extend the fuel line and place the primer bulb at the far end of it, so you can get the siphon going, and then remove the bulb to allow faster flow. Alternatively, an electric fuel pump is less than $15 at amazon.


My fuel gauge read empty when the 18Gal tank is at 1/3, and each 3 gal of fuel changes the gauge by 1/4 tank. So 12 Gal is 1/2 tank, 15 gal is 3/4 tank etc. It is consistent.
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I am of the opinion that tank/meter mfgrs. deliberately set the E on the gauge with some level of fuel in the tank for safety's sake. I think I verified this over the years but have no exact instance nor exact measurement. Besides an "almost" empty tank is unreliable, especially in a boat with varying degrees of tilt due to speed, load, and water conditions.
 
nola mike

nola mike

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One of the many things that I've considered doing is to just splice in a rheostat so that I can in fact fine tune the fuel gauge. I don't rely on it at all though...I track how far I've gone every time I fill up, I get about 4 mpg on a 27 gal tank, never go farther than 80 miles before refueling.
 
Scott Danforth

Scott Danforth

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I follow both the 1/3 rule and 1.5mpg rule on my boat.

down to approx 5/8 of tank and turn around to start heading back

assume 1.5 mpg, and at 80 gallons, most distance I can travel is 120 miles (boat gets better economy, and I have gone farther). typical trip is 60-100 miles
 
A

airshot

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Ifishmuskie2 said:
I ran my kicker that has a 12L tank until it ran out of gas. I then marked the tank with magic marker to tell where empty is. 6L of gas is about 15hrs trolling at 3mph. I wrote that on the tank too.
Now I’m wondering about the on board tank. The fuel gauge is not very accurate.
I’m thinking about draining it through the fuel line that goes to the engine. Then I’ll know where empty is. Then I’ll install a new bobber style sender and mark the gauge where empty is.
Any thoughts on this?
Click to expand...
Been doing that for years, my current boat has a built-in 18 gallon tank but only 17 gallons is usable to the motor. Carried a portable tank and ran until main tank stopped . then added three gallons at a time and marked the gage for each three gallons. Now, I know how much fuel I gave used or how much I have left within one gallon accuracy. Been good for the past 5 years, I use about 3 gallons for each trip out and back, when I get down to about 4-5 gallons, I always fill up on the way home so it is ready for next trip.
 
C

cwella

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Jul 10, 2026
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Ifishmuskie2 said:
I ran my kicker that has a 12L tank until it ran out of gas. I then marked the tank with magic marker to tell where empty is. 6L of gas is about 15hrs trolling at 3mph. I wrote that on the tank too.
Now I’m wondering about the on board tank. The fuel gauge is not very accurate.
I’m thinking about draining it through the fuel line that goes to the engine. Then I’ll know where empty is. Then I’ll install a new bobber style sender and mark the gauge where empty is.
Any thoughts on this?
Click to expand...

That should work, but I'd avoid running the tank completely dry if possible. Draining it through the fuel line is a better option, and once you know the true empty point you can calibrate the new sender much more accurately.
 
T

tank1949

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Apr 4, 2013
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Ifishmuskie2 said:
I ran my kicker that has a 12L tank until it ran out of gas. I then marked the tank with magic marker to tell where empty is. 6L of gas is about 15hrs trolling at 3mph. I wrote that on the tank too.
Now I’m wondering about the on board tank. The fuel gauge is not very accurate.
I’m thinking about draining it through the fuel line that goes to the engine. Then I’ll know where empty is. Then I’ll install a new bobber style sender and mark the gauge where empty is.
Any thoughts on this?
Click to expand...
Depending on age of boat/tank, it may be a great time to pull, examine and paint it again. Once out of boat, you can calculate the volume where bobber reaches and determine how accurate fuel system reads.
 
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