CD31 diesel tank

[12Sail]

From the "no such thing as a stupid question" department.....my diesel tank is in the port side cockpit locker, probly just like every other 31. I'm curious if the gauge on top of the tank is accurate (shows about 5/8 full), because when i "knock" on the side of the tank, it sounds dead empty.
1) is the tank perhaps doublesided, so that it would make an "empty thunk sound" even if full?
2) might that not be my real tank, and there is another one somewhere? I don't think that's the case....
3) any suggestions on how to check the fuel level? Im thinking something like a dipstick might make sense, but not sure that's a good idea.

Thoughts?

[Neil Gordon]

Do you know the size of the tank? If so, a quick trip to the fuel dock will confirm if a 5/8 reading on the fuel gauge is accurate or not.

If you don't know the tank capacity, there might be an extra step or two.

I'm not sure about what you're hearing when you tap the fuel tank, but the acoustics of a sailboat hull are much like those of a guitar. The empty sound you hear might be the cockpit locker and not the fuel tank.

[Duncan]

My fuel gauge is a 5/8" socket (for weight), tied to the end of a polypropylene line (the cheap yellow stuff). It snakes down the filler pipe, until the socket hits the bottom. I "gauge" the amount of fuel from the length of line that's wet when I pull it up.

Anyway, the socket hit the bottom this morning with a thunk and, same as you, I thought the tank was empty. But when I pulled up the line, the last two inches were wet (i.e. around 1-2 gallons).

So, definitely, the tank can sound empty, even when it has fuel in it.

[JWSutcliffe]

The tank on my 31 reads fairly accurately - if anything it reads a bit low.

[Jim Walsh]

I vote with Neil. Fill it and you'll know. I replaced mine two years ago and my gage is pretty accurate.

[Jim Davis]

Keep a fuel log. Every time you refuel log the hours and quantity. This allows you to get a fairly accurate gestimate of fuel consumption and acts as a backup to pesky gauges. I do all my fueling based on hours and have actually removed the gages.

My fuel log is actually an engine log as I also keep oil and filter changes as well as other servicing.

[Steve Laume]

If you have an aluminum tank it is single walled and will sound pretty hollow when you tap it. It was also, most likely made by Florida Tanks. It will have a sticker on top that will give you the capacity.

I would follow the advice to fill it and see how that compares to the reading. The gauge is a very simple mechanical device. Unless it is stuck in place I doubt it would ever read high. If the cork float on the end was somehow defective it could read low but that doesn't seem to be your concern.

I have a feeling all is well in your tank world but keep an eye on it for corrosion problems on the underside, Steve.

[Phil Shedd]

12sail

I find the fuel gauge on mt CD31 to be quit accurate . When it is at full it is full. Seems to drop at a constant rate while under way. I base my fuel usage at 8 hr per quarter tank running around 2100 rpm.

However to be on the safe side I never let it get below 1/4 .

Phil

[12Sail]

All, thanks for the insight and suggestions. I don't run the engine that much so was hesitant to fill it up only to have all that fuel sit over the winter. But i do agree that filling it to capacity and doing some math is the simplest and best way to create peace of mind.

[sgbernd]

I assume you have the Florida tank and cork float. There are a half dozen metal machine screws securing the gauge to the tank. It is easy to remove and look inside with a flash light. This is also a good chance to replace the rubber gasket seal (West Marine has them for about $7) and look for any signs of water, debris, algea, or contamination in the tank.