Fuel Gauge Calibration

[tdonoughue]

Ok, I have searched and cannot find it on here. There are references to doing the 'calibration trick' on the fuel gauge, but no instructions on how to do that trick.

Filled up today and the gauge is still at 3/4. I thought last time I just had not gotten it full. This time I definitely got it full, but the gauge is not cooperative.

I guess I will be meeting the sensor in the tank soon... Can anyone shed any light on what I am up against?

 

[Andy S]

Below is a picture of a sending unit, same as what is in my boat, probably similar to yours. One thing about these sending units, the type of fuel, i.e. the density, in your tank will effect the reading on the fuel gauge. If you always use non-ethanol fuel and then add fuel with enthanol or vice a versa your fuel gauge will probably read wrong.

Typically there is some epoxy over top of the adjustment screws. Make sure the tank is full before making adjustments. Since you are only having issue with your fuel gauge not reading full then you will only have to adjust the Full screw. After making the adjustment, I would then remove the fuel sending unit from the tank to verify that it fuel gauge reads empty. If you don't like the low fuel gauge reading then you will have to adjust the Empty screw. Go back and forth between full and empty adjustments until you are happy with the fuel gauge readings. Once done you can put a little dab of caulk, any type will do, on top the adjustment screws, this will help prevent them from moving due to vibration.

 

[Murf'n'surf]

X's 2 on andy's comments.
I'll add that the sensitivity of the pots are very high. Turn very slowly!

 

[tdonoughue]

Excellent. I can do that. Thanks gents!

Oh, and been using the same fuel its whole life, so no issue there.

 

[tdonoughue]

Coda:

So I went out to fill up today, fully intending to do the aforementioned procedure. Filled (man, it took a lot--41 gallons... Much more than last time), started and.... Gauge at full.

Lesson:

Don't trust the gas pump turning off... Check that prior to recalibrating!

 

[MOA_Chaser]

Glad that's all it was. I filled mine up at the beginning of the season and it was reading 3/4. I tried to adjust it, but I'd just TOUCH the screw and it would peg out hard way past full. Any discernable movement one way or the other would result in either 3/4 or pegged full. I left it at full but I don't trust it. It never moved smoothly at all for me.

 

[Julian]

I've wondered about replacing my sender with a different one that doesnt have a problem reading gas and ethanol. Anyone thought about doing this?

 

[Andy S]

Here is a calibration procedure from the manufacture, http://www.centroidproducts.com/3wire.htm

This is a float unit that Yamaha has used on some models, http://www.wemausa.com/sensors/level-FuelWater.shtml . From the other forum here is a quote from another member back in June 2009,

"I spoke to a representative at WEMA today. They said I can use their sending unit in my boat, which is good since it costs $45 compared to $100 for the Centroid. Also, The WEMA does not get its power directly. It gets it from the gauge which is why there is only two wires. Also, WEMA uses a "float" where Centroid uses Capacitance."​

If you go with the WEMA unit, you will need shorter mounting screws, 3/4" SS #10-24, due to the head being much thinner.

 

[TechRider]

Anyone else go from 1/4 tank to low fuel warning very quickly? It seems to stay at about 1/2 tank for a long time then goes quickly to 1/4 then very quickly warning.

Does anyone know how much fuel is in the tank when the warning starts?

 

[Gym]

You can try the above calibration method but it sounds like the sending unit is too erratic. I suspect you may need to replace it but @Julian seems to have found a good inexpensive alternative.

 

[Julian]

Investigating further, this may only be an issue for those of us with older (need to call them and find out when they added the full sensor auto recaibration). Here is info from their website:

"FUEL SENDERS:
Conductivity: Centroid's fuel senders (CGFP-..., CGOP-...) require the fluid being measured to be non-conductive.
The conductivity of E10, which is gasoline with up to 10% ethanol, is sufficiently small to be acceptable unless the alcohol
falls out of solution (phase separation). E85 (85% ethanol) conducts too well for our fuel senders to work with it.
Dielectric: the capacitance we measure is proportional to both the liquid's height and the dielectric constant of the
liquid being measured. Gasoline without ethanol has a nominal capacitance of 1.27 picofarads of capacitance per inch
with our 1/2 inch tubing. But gasoline with 10% ethanol has twice that capacitance, and the percent ethanol in the United
States can be anywhere between 0-10%, ignoring E85. To correct for this variability, in gasoline applications we use a
scheme we call Full Detection where the sender detects a fillup and rescales the calibration if the reading would otherwise
be something other than Full due to the percentage ethanol. Diesel doesnt contain ethanol and we normally dont turn on
Full Detection for diesel, though we can. For a Full Detection to occur the sender must be filled to within several inches of
the top with power off. The Full Detection then occurs at powerup.

Dielectric: A liquid's dielectric is affected by the composition of the liquid being measured. Because we dont have control over the
dielectric constant of the liquids we measure, we never specify an accuracy figure for measurements with actual fuel.
Instead, we calibrate and test senders using capacitors equal to the nominal capacitance of diesel in a diesel application,
or the nominal capacitance of E10 (plus turn on Full Detection) in a gasoline application. We've been selling senders
successfully for about 25 years, even before we had Full Detection, so historically people have gotten the accuracy they
needed without us being able to promise a particular accuracy. "

http://www.centroidproducts.com/warr-2-1-2014.pdf

 

[tdonoughue]

Wow! Now that is way cool. Thanks for that @Julian . Had no idea my boat was so smart...

 

[Julian]

Centroid says the we should only need to adjust the full setting, and if we have a model CGFP (the P being the key), then it will have a full sensor auto recalibration.

I'm looking into ordering a new sender that has the auto recalibrate function. Has anyone measured the length of their sender?

 

[MNdrifter]

I'm not comfortable posting the length of my sender on a public forum

 

[MOA_Chaser]

Just tried to calibrate again yesterday after filling it. I can set it to over-full or just under a half tank. There is no way to get it anywhere close to the "full" mark when it's full. Sigh.

 

[Gym]

Just tried to calibrate again yesterday after filling it. I can set it to over-full or just under a half tank. There is no way to get it anywhere close to the "full" mark when it's full. Sigh.

That means the "F" potentiometer is shot. You'll need to replace the sending unit.

 

[MOA_Chaser]

That means the "F" potentiometer is shot.

Yippee! So... what's the smallest part I can replace to fix that? The whole unit mentioned above (~$100)?

 

[Julian]

@MOA_Chaser Should be able to just change out the sender...which is what I'm planning on doing, but first thing we need to know is the length of the sender - and I don't have my boat handy, and every time I go boating I have a bunch of kids around....

 

[Murf'n'surf]

The tank measurements should be stamped on the tank near the sender.

 

[Big Shasta]

Lesson learned, search here first before attempting what seems like the easiest of part replacements. I would have saved myself a lot of hassle shown here:
https://jetboaters.net/threads/05-ar230-fuel-gauge-sender-swap.3672/#post-62142