Fuel sender reading three quarters full when tank is empty.

[Bavnav]

I had the engine serviced today, thought it would be straight forward as usual. Not this time. I ran the engine on Sunday to check everything was Ok. before service - Bavaria 30 c.,Volvo 20 hp. Engineer changed primary filter etc. however, there was no fuel coming through when pumping. Worked through the fuel system to no avail. Decided to check fuel tank and lo and behold - no fuel! He did ask me earlier if the tank was fairly full. The fuel gauge had been reading reading three quarters full. I have always kept it 3 quarters full to full and when over 3 quarters it registered correctly. It turned out that the fuel sender was giving a false reading- the gauge reading 3 quarters to full when indeed it was empty. This could have been a problem had we gone out. Has anyone else had this problem?
Fair winds,
Bavnav.

[Craig]

The fuel readings have always been out, but not to this extent in my experience.

For all new boats, not just Bavarias, I recommend that a calibration of the gauge is done. Start filling with the tank near empty and record how many litres of fuel take the reading to 1/4 full, 1/2 full, 3/4 full, full on the gauge and when tank is actually full.

On my 2009 Bav 38, 1/2 full on the gauge is actually 1/3 full.

Craig
"Shirley Valentine"
Gold Coast
Australia

[Sweet As]

Not an uncommon issue with fuel tanks on yachts. The gauge often assumes a linear relationship between liquid height and volume. Due to the tapered nature of many tanks this is seldom correct. I estimate fuel use from engine hours run. Our 29Hp engine burns 1.8L/hr, up to 2L/hr if it is really pushed.

[Lyra]

I agree that the best practice is knowing the average hourly fuel consumption and tank volume and keeping record of engine hours.
I keep a log of all fueling, typically to full tank, and thus able to keep a log of average consumption. This serves me especially when planning long passages to estimate maximum engine hours and the decision how many portable tanks to carry.

BTW I always keep a full 20 liter portable tank with various lengths of spare fuel lines. You can never know when you will be stuck without fuel, not only due to low level in the main tank but rather due to a problem that prevents fuel flow (contamination in the tank, blockage of passages, defective lift pump etc). With a portable tank you can always connect it temporarily after the primary filter, or  above the engine after a defective lifting pump, and get several engine hours. During routine refueling this tank is emptied into the main tank and refilled.

[Nigel]

The gauges are not very accurate, but this sounds like a faulty sender; if you remove it you can check. A European resistance fuel sender will measure around 10Ω empty and 180Ω when full, this is the most likely type. An American resistance fuel sender will measure around 240Ω empty and 33Ω when full.

[Lyra]

A European resistance fuel sender will measure around 10Ω empty and 180Ω when full, this is the most likely type. An American resistance fuel sender will measure around 240Ω empty and 33Ω when full.

A bit out of topic - but is this resistance also valid to the water and holding tank senders? If not - do you know what they are?

[Bavnav]

Thanks for all the helpful replies. We have established the sender is faulty and we know need to source a new one - any ideas where?
I will also replace the fuel gauge, which has become rusty. The readings never fall below 3 quarters of a tank, so just in case will be replaced. I would appreciate some help with sourcing these items - gauge and sender, 90 litre tank. Good ideas about establishing fuel per hour.
Fair winds,
Bavnav

[Symphony]

It will be a standard type VDO sender. You need to get it out to establish the exact variation and look it up in the catalogue on the VDO website. I got mine from  Demon Tweeks in UK. However there are several possible suppliers if you google it.

[Bavnav]

Yes it is a VDO. I will try your suggestion, Symphony.
Fair winds,
Bavnav.

[Nigel]

A bit out of topic - but is this resistance also valid to the water and holding tank senders? If not - do you know what they are?

In general, yes. However, my original water senders were dip wires that only gave four steps, now replaced with USA senders and a DIY gauge.

[tiger79]

Newer boats use ROAD fuel senders. They're just as inaccurate! 

[DT]

Talk to it about the GFC and global warming and it will stop this glass 3/4 full nonsense.