Beneteau Oceanis 40 fuel gauge is inaccurate

[AFKASAP]

I am sure that you would assume it to be inaccurate, but I can confirm that it really is (at least on my boat).

Ours is a 2008 2 cabin version, which is supposed to have 200L tank.

My tank showed a little under half full and when I filled up and I managed to put in 187L. So either the tank is bigger than rated or the gauge is very inaccurate.

Anyone have info on this?

Sent from my GT-I9500 using Cruisers Sailing Forum mobile app

[Sailmonkey]

Show me a gauge that is accurate after about a year.........


Sent from my iPhone using Cruisers Sailing Forum

[Cheechako]

It's often due to the shape of the tank, but on a cat... maybe not.
If it's just a rectangular tank, remove the sender unit and check that the float arm is long enough to go to the bottom etc etc. No builders spend any time trying to make them accurate is my impression.
If its an odd shape tank, you are likely out of luck, but should be able to get it closer than what you have via adjustment!

[jamhass]

You can calibrate the gauge yourself. If the tank is empty (or near so), note the reading and start adding fuel. Every 10 gallons or so, note the reading and how much fuel you added. Next time you will know.

If the tank is not empty, just do the same every time you fill up, log the info and eventually you will have a pretty complete calibration table you can add to your fuel log.

[gonesail]

sounds like the sender may be toast.

[AFKASAP]

I have not done any tests but I suspect that it is because the tank is an irregular shape. It gets narrower at the bottom.

Sent from my GT-I9500 using Cruisers Sailing Forum mobile app

[paulajayne]

Sound like iffy sender unit.


2008? - so has been in there for 7 years - replace it.

[edsailing]

That sounds very typical. I have delivered a few and at first you think the engine is very economical - then a top up becomes a big refuel! I think it is a design or quality issue, probably you need to live with it. Keep a log of engine hours and refuel on that.

[AFKASAP]

I believe there is nothing wrong with the sensor. It is just not calibrated to take into account that the tank gets narrower at the bottom.

Sent from my GT-I9500 using Cruisers Sailing Forum mobile app

[nigel1]

I think most Beneteau boats are fitted with VDO lever arm type level senders.
Been having problems with my one, and removed from the tank. Checking with a meter between the two contacts it showed open circuit.
Have removed the float unit from tank and looks like a connection is missing. Between the sweep arm and it's connector I get a continuity, but between the resistor bridge (not sure that is the correct term) and its connector, no continuity.
On close inspection I can see a solder blob, but nothing in it, so I soldered in a wire to make a connection.
Now I get a resistance range of about 10 to 200 ohms which looks about right.

Some research indicates that US level senders have a range of
240 ohms Empty, 103 ohms half, and 33 ohms full

European Senders
10 ohms empty, 95 ohms half, and 180 ohms full.

Of course, with the tank shape, the sender will only measure liquid height at the place where the sender is sited, and not volume.

The VDO senders have two adjustments to allow for tank height, have attached the installation instructions which includes a table of what these adjustments are.

Also, a good clean of the unit itself will help.

In trying to trouble shoot the problems with my sender, I came across this type

SSS/SSL Diesel, Fuel or Water Level Sensor (4 - 60 in.)

which looks a lot more robust than the VDO type, and more suitable for a boat than the lever arm type.

[sck5]

keeping track of engine hours and gallons put in will give you a better idea of where you are than the gauge will (at least if your boat is anything like mine have been)

[sck5]

an even better way to keep track if you have a straight line fuel fill pipe: get a wooden dowel that reaches to the bottom of the tank and make marks on it. Foolproof if your boat is set up so that it is possible.

[a64pilot]

Originally Posted by nigel1

In trying to trouble shoot the problems with my sender, I came across this type

SSS/SSL Diesel, Fuel or Water Level Sensor (4 - 60 in.)

which looks a lot more robust than the VDO type, and more suitable for a boat than the lever arm type.

My 27 yr old water tank sensor was inop, I replaced the old float arm type with the one you have pictured, and it works perfectly, with the original gauge and wiring.
Astonishingly my fuel gauge works and is very accurate as I had expected an inaccurate gauge at best, so it is possible to have both an accurate and a reliable gauge.

[a64pilot]

Originally Posted by sck5

an even better way to keep track if you have a straight line fuel fill pipe: get a wooden dowel that reaches to the bottom of the tank and make marks on it. Foolproof if your boat is set up so that it is possible.

Often there is another set of access plugs meant for generator installs, you can remove one of those easily to "stick" your tank, a clear glass or plastic tube is what is used in aircraft, just put your thumb on the tube to hold the fuel level of course.
Just be darn sure your tube or stick or whatever is long enough so you can't accidentally drop it into the tank. I had a heck of a time getting one out of an airplane gas tank.

[nigel1]

Originally Posted by a64pilot

My 27 yr old water tank sensor was inop, I replaced the old float arm type with the one you have pictured, and it works perfectly, with the original gauge and wiring.
Astonishingly my fuel gauge works and is very accurate as I had expected an inaccurate gauge at best, so it is possible to have both an accurate and a reliable gauge.

I'm just about to order one. Fortunately, Wema have a subsidiary in the UK, which has made the process easier, and these are made for the European market.