Fuel gauge wildly inaccurate, is that typical?

[jsc7]

I have a Boston Whaler, a well-built boat, but the electronic fuel gauge is wildly inaccurate.

For example, the tank supposedly holds 291 gallons, but if I fill it up, it reads 262.

I can put 50 gallons in the tank and the gauge will not change. For example, the gauge reads 150. I add 50 gallons. The gauge does not change.

Yesterday, I had 100 gallons in the tank (according to the gauge). I added 100 gallons (metered). The gauge then read 162.

Is this typical for boats, or should I investigate removing the OEM (Boston Whaler) gauge and replacing it with something different?

[Dockhead]

Typical for boats. Ordinary fuel gauges are not intended to give you an accurate to the gallon read of fuel state; just a general idea. Most people calibrate their gauges in their heads -- they know that fuel is actually down by 100 liters (or whatever) when the needle first moves off Full, and that you've still got 100 liters (or whatever) when the needle first touches red, and everything in between is a rough approximation.


If you want to know your fuel state with accuracy, then you really need to invest in flow meters, the way they do it on high end power boats. Know how much is in your tank, then set the flow counter to zero when you're full, and you will always know very precisely where you are.


And/or:


Buy a good fuel sensor and calibrate it. Maretron make an ultrasonic one which can be programmed and calibrated. Or there are pneumatic ones ("Tank Tender") which will tell you the static pressure at the bottom of the tank, and you read that against a calibration card which translates that into the quantity of fuel remaining.




All of this is quite a lot of expense -- do you really care? Most people just learn to interpret what their carpy original fuel gauge tells them, and learn the limitations of it.

[Sailmonkey]

I’ve never been on a boat with an accurate fuel gauge that wasn’t a sight tube.

[Attikos]

My fuel, water and holding tank gauges all are wildly inaccurate. Replacing them doesn't help. You learn to read levels by other signs.

[scotty c-m]

I agree that fuel guages are often inaccurate. However, the gauge described by JSC7 sounds different. You should get some consistancy from your gauge, and that helps when using it. I would explore getting a more consistent gauge.

[Fence Man]

Every boat I've owned showed empty on the gauge(analog) at right around half a tank. I don't know if there is a reason for that, or if I'm just lucky.

[sailjumanji]

I have a fishing boat with a very shallow but long and wide tank. Holds 60 gal fuel. Motor is 250 hp Yamaha SHO. Gauge very inaccurate so I hooked up the motor ECU to the NMEA network. Now my Garmin plotter gets instantaneous fuel consumption and integrates to show me "fuel remaining". Very accurate. When you add fuel you enter into Garmin and setting gallons added. Just as good as having accurate fuel remaining is having the instantaneous fuel consumption number. I think my motor burns 6-7 gal per hr at 25 mph and over 30 gal per hr at WOT of 50+ mph.

[ranger58sb]

Some senders -- float arm senders -- can sometimes be slightly adjusted. Pull it out and yutz with it.

Sometimes associated gauges can be adjusted; check the manual.

Sometimes a "general idea" is about as good as a given sender/gauge pair will get, sometimes inhibited by sender and/or gauge, but also very dependent on tank shape versus sender type.

For example, the quantity of new fuel injected into a tank with a deep V at the bottom will have a different affect on sender float height (or change in height) than might that same quantity at the higher part of the tank.

And in the grand scheme of things, senders using resistance curves to inform gauges... aren't rocket science... and in turn they're just not as accurate as rocket science. Another example of that might be when the sender is near the aft section of the tank; often that means fuel height in the aft part of the tank will increase when you're underway; sender float rises, gauge displays more fuel than you had at rest.

-Chris

[Chalifour]

Best fuel gage you can get is you! Simply know how many liters your engine consumes per hour and than keep track of the engine hours from fill up to fill up.
Only requires that you fill up full every time.
Than you can sell your fuel gage !!!

[Pete7]

I use a garden cane with marks for every 5 gallons.

However, as Dockhead said there are meters based on the flow rate of fuel to the engine. Reasonable prices for petrol engines.

Pete

[ArmyDaveNY]

Originally Posted by Dockhead

- do you really care? Most people just learn to interpret what their carpy original fuel gauge tells them, and learn the limitations of it.

Excellent point. None of my boats even have a fuel gauge. They have a stick that I dip into the tank so I can see roughly how much is left. I know how much the tank holds and I know my approximate fuel burn rate. Often I don't even use the stick. When I think I am getting low I may check with the stick or more often I just pump some fuel from the jerry can into the tank and use the stick to see how close to full I am getting.

[Cheechako]

It's typical for most boat gauges. The tanks are odd shaped or V shaped and it's not a linear measurement. Knowing your average usage per hour and logging that helps. Then adjust your gauge so it measures accurate-ish on the last half of the tank to know when you are getting low is about all you can do.
There may be new fangled programmable electronic types out there now...?

There are fuel flow meters that go in your fuel line available (like aircraft use).

[FabioC]

I guess it depends on the boat.

On my boat, the fuel gauge always indicates full, no matter how much fuel is in the tank... (well, I only tested down to 1/4 of a tank, still "full"). I had a mechanic opening the tank and testing the gauge, and apparently it is working fine, it is likely the shape of the tank that makes it inaccurate.

Tank Tender or similar devices sound like an excellent idea. Expensive, but they are certainly at the top of my wish list for next season.

[winddrifter]

I removed the fuel tank gauge and it appeared to be in good working condition. After testing the gauge with an ohm meter I found the rheostat worked nicely when the float was in the high tank level position but below half tank level the rheostat showed and open circuit. The rheostat was an open type so I scratched the corroded area with my pocket knife and retest. Now the gauge worked down to one quarter tank before showing and open circuit which was still not working good enough. Ebay sells the gauge assembly but I would like to get just a new rheostat.

[Chuck Hawley]

Boat tanks are frequently wide, flat, and oddly tapered to fit compactly against the hull. Any motion of the boat tends to cause some sloshing, and boats that are not trimmed (or bow-high due to being on a plane) will show inaccurate readings. It's a tough challenge.

I have a few thoughts that might help, however.

1. Change to a fuel consumption meter so you can "zero" your tank when full and measure how much you consume.
2. Swap out your sensor for a better model. Not sure what you have now, but the lack of smooth increase/decrease means to me that you might benefit from a WEMA or similar sensor.
3. Some readouts calibrate the tank to peculiar, non-linear tank designs. Blue Sea Systems, for example, allows you to take an empty tank and fill it at a constant rate, which calibrates the tank despite odd shapes.

Cheers,

Chuck Hawley