Fuel gauge showed full tank but I knew otherwise

[baz]

The other day I wanted to fuel up and I knew my tank level was at around 56 gallons yet my Garmin dashboard fuel gauge and the Yanmar fuel gauge were both showing the tank was full. A quick call to Andrew resulted in Andrew advising me to take boat out in some chop and see if that dislodge the presumable stuck sensor in the fuel tank. I did so, but it did not resolve the issue.

I had opportunity last Tue to take the boat out for about 4 hours and while most of the trip was in relatively calm waters the last part was with considerable chop and and into 15 mph wind. I noticed after this the fuel gauges returned to accurately indicate correct fuel tank level.

Lesson here is to keep good records of fuel fills and not to depend entirely on the fuel gauges. I mean to say had I only 10 gallons of fuel aboard and trusting / believing fuel gauges saying I had a full tank could be disaster not worth thinking about.

 

[knotflying]

I thought the Garmin fuel guage recieved its information on fuel based on the fuel flow not from the float in the tank, hence why you have to enter fuel added each time you add fuel. Am I mistaken?

 

[baz]

I thought the Garmin fuel guage recieved its information on fuel based on the fuel flow not from the float in the tank, hence why you have to enter fuel added each time you add fuel. Am I mistaken?

I asked this of Andrew, and if I'm not mistaken and if I understood him correctly, he said the Garmin's dashboard analog fuel gauge reads same sensor as for the Yanmar analog gauge or simply reads/displays the Yanmar fuel gauge readout.

I always reset my "fuel aboard" in the Garmin display when I fill the fuel tank to 75 gallons. I will be using this from now on as that seems to be a more accurate method for indicating fuel left in the tank.

 

[knotflying]

You may be right, but quite frankly I always have the fuel burn info on my screen I never believe in the guages. It must be the pilot in me. I prefer to use a conservative burn rate per hour and check that against the Garmin information and you are far more accurate than looking at a guage that is dependent on what attitude the boat is in. Hey, go full throttle and you will always have a full tank, until you run out of fuel, that is. At least in a boat you just stop, a very different story when flying a plane.

 

[JamesTXSD]

Boats are notorious for inaccurate (or non-functioning) fuel gauges.* Even though we have a fuel gauge and a fuel flow metering system that are accurate, I still keep track of hours run since fueling when we are cruising. With a track record of fuel use over thousands of miles and conditions, our estimates of fuel use are pretty darn close to what the fuel flow meter says.

Regarding being a pilot: the only time a fuel gauge on an aircraft is required to be accurate is when it reads EMPTY. And, aircraft can be prone to some unusual attitudes, too. 😉

Best wishes,
Jim B.

* My favorite fuel gauge story: I did a relief captain job on one boat where I asked the other captain about the fuel gauges. He said, "They aren't hooked up. The CG inspector wrote them up for not having fuel gauges on the boat, even though they "dip" the tanks (put a stick inside the tank to visually check the level - more accurate than any gauge). So, they put in a gauge for each tank, set them at half... when they are inspected, they "always have half a tank." 😎