You have to be careful on how these issues can be translated. Each engine manufacturer has a different way to monitor the fuel and how they are programmed. The one thing these all have in commons is that a standard style sender is used in the tank. The sender used is either a Rochester or Wema sender both reading the same range of ohms to measure the tank size. The sender will read 30 ohms in the full position and 240 ohms in the empty position. The size, shape and orientation of the boats fuel tank does matter and will provide different readings. Here is a short outline of how the sender works with the different engine packages.
1. Volvo Engines
a. Volvo is based off a calibration to setup the sending unit when the engine is first installed.
b. You have two ways that this calibration can be performed.
c. The first way is called an "empty/full" calibration. This is a simple calibration that you do through the Volvo control display that you tell the Volvo when the tank is empty (or sender is placed in the empty position). Then, you tell it when it is full and it uses that calibration.
d. The second way to calibrate is a multi point calibration which is not how we calibrate at the factory. You would have to start with an empty tank and fill in 5 gallon increments to tell the Volvo each time 5 gallons is put in until full.
2. Yanmar BY Series engines
a. These engines are a plug and play and require no programming to make the sender work. It is pre set to be a standard style gauge reading or European style which we do not use for our ohm range senders.
We have seen many times where a computer or update is done to the Volvo where it will wipe out these calibrations and you have to reprogram the fuel sender or it magically disappears which might have happened with Mark's boat. All of our new models have the fuel sender accessible where it could be removed and programmed if you questioned the way it was calibrated and just to be sure. You would undo the bolts holding the sender in and go into the Volvo control and perform a new fuel calibration holding the sender to the empty and full settings. Pretty easy to do and a good verification.
Personally, I never rely on any fuel sender (and that goes for every single boat I have owned). The senders work but not knowing the exact fuel has always worried me. Fortunately for you Volvo and most Yanmar owners, you have a way to monitor the fuel used on the Garmin which is taking the fuel burn provided from the engines. The garmin calculates the fuel used from the engine monitor and gives you a remaining gallon feature which is very accurate. This setting does require you to update each time you add fuel but will be within a couple of gallons if done right. You can search another thread I did on here about fuel programming to see the steps to do that.
