Fuel gauge sender

[dbirken]

The fuel tank on my C320 is not quite a cube but instead much deeper along the forward section than aft. The fuel level sender is positioned in the deeper part of the tank forward. I have just returned from a ~14 hour motor and filled up just before leaving. The gauge still reads full after returning and I ran pretty hard (3000 rpm) so I assume consumption was at least 1/2 gal per hour or more.

The sender was just replaced 2 years ago. Any ideas on how to calibrate this? Do I need to replace sender? How do I compensate for a trapazoid shaped tank? Anyone with experience on this?? I appreciate all thoughts.

Dave

 

[sail sfbay]

Welcome to the forum!!

Is the sender ohm range paired with your gauge? If it is check the voltage and resistance (ohms) with a multimeter. Follow this stepwise troubleshooting guide Troubleshoot Your Boat’s Fuel Gauge | Boating Mag AND/OR How to Test and Replace your Fuel Gauge and Sending Unit - Sail Magazine to determine why it is not working.

 

[jssailem]

Dave.

Fuel volume guages are notoriously inaccurate. For all the time I have been using a boat, the guage is a convenient indication of the approximate volume in the tank...

• Full - Smile. Someone left the boat with fuel in it. That is if the sender is still working.
• 0.5 full - Oh well I can get in and out of the marina. Better start considering my next fuel stop.
• 0.2 full - Damn. Have I been going that long on the motor? Why aren't the sails up? Better fill the tank at the next port.
• 0.0 full - Well I know the tank has maybe another 2 gallons... Better save the fuel. I wonder if I can sail up to the fuel dock. Maybe the sensor is broken.

Or

• you can open the tank and dip a stick into the tank to get a physical reading.
• You might also install a sight glass to show the fuel. It is a bit of a pain and if not installed correctly can leak all that precious fuel into the bilge.

More simply, choose a value - 1/2 gallon per hour. Fill the tank. Motor about for 2 hours. Refill the tank and see if your calculations are correct. 1/2 gallon per hour or maybe 3/4 gallons per hour.

Now start a record of your fuel consumption and the number of hours you have run the motor. In a short season you will accurately know the fuel consumption rating of your engine. You will know if you suddenly start burning more fuel than normal - time to look at the engine or search for a fuel leak. It is the tried and true way to know your fuel usage. You will also be able to know if you have enough fuel to motor home that 14 hour trip or if you should wait it out until the wind comes up and sail closer to port before starting the engine.

Welcome to the forum. Sounds like you have a lot of sailing experience. New boat to you?

 

[kappykaplan]

Fuel volume gauges are notoriously inaccurate

Mark 1 Mod 0 eyeball is the best fuel gauge.

 

[dbirken]

Dave.

Fuel volume guages are notoriously inaccurate. For all the time I have been using a boat, the guage is a convenient indication of the approximate volume in the tank...

• Full - Smile. Someone left the boat with fuel in it. That is if the sender is still working.
• 0.5 full - Oh well I can get in and out of the marina. Better start considering my next fuel stop.
• 0.2 full - Damn. Have I been going that long on the motor? Why aren't the sails up? Better fill the tank at the next port.
• 0.0 full - Well I know the tank has maybe another 2 gallons... Better save the fuel. I wonder if I can sail up to the fuel dock. Maybe the sensor is broken.

Or

• you can open the tank and dip a stick into the tank to get a physical reading.
• You might also install a sight glass to show the fuel. It is a bit of a pain and if not installed correctly can leak all that precious fuel into the bilge.

More simply, choose a value - 1/2 gallon per hour. Fill the tank. Motor about for 2 hours. Refill the tank and see if your calculations are correct. 1/2 gallon per hour or maybe 3/4 gallons per hour.

Now start a record of your fuel consumption and the number of hours you have run the motor. In a short season you will accurately know the fuel consumption rating of your engine. You will know if you suddenly start burning more fuel than normal - time to look at the engine or search for a fuel leak. It is the tried and true way to know your fuel usage. You will also be able to know if you have enough fuel to motor home that 14 hour trip or if you should wait it out until the wind comes up and sail closer to port before starting the engine.

Welcome to the forum. Sounds like you have a lot of sailing experience. New boat to you?

Ha! Thank you ! That really is the correct answer isn't it. I really appreciate your reply. I've had the boat 13 years. I grew up on a Coronado 25 and sabot sailing in Channel Islands harbor in CA. 13 years ago took the plunge so my kids could have a similar life experience. I've really enjoyed the boat but not knowing when i am going to run out is slightly unnerving.

Have a great day.
Dave

 

[sail sfbay]

Happy to say the fuel gauge on my Hunter 46, ski boat and powerboat are spot on. The powerboat required a new fuel sender since the previous owner installed a sender an incorrect ohm range.

However, I do monitor cumulative engine hours so have a relatively good idea of fuel consumed / remaining in the tank after fill upindependent of the fuel gauge.

 

[smokey73]

When I replaced my fuel tank with a new one from the OEM (Ezell in FL) I filled the tank 5 gallons at a time and recorded the fuel gauge level indication at each 5 gallon increment. It is on the conservative side in its reading (when it says 1/2 full its about 23 gallons, not 2o gallons) and when its says 1/4 full it is about 13 gallons not 10 gallons). I keep track of every drop of fuel put in, the hours run on both the engine and the generator. Having the generator complicates the estimate of usage.

If you are interested in using your fuel gauge, I'd empty the tank (siphon it out from the fuel sender hole - its a good time to get rid of anything on the bottom that way.) After you figure out if you have the right fuel sender/fuel gauge ohm match, fill the tank in 5 gallon increments and record the level shown for the actual fuel in the tank. Put the numbers in your ship's log or post it just below the gauge. Even at that, the gauge is just a "rough" estimate. Use the fuel usage/hours run as your main indicator. Just my 2 cents.

 

[Benny17441]

Calculate your average burn rate (Gallons per Hour), find out your tank size in gallons and deduct 20% for reserve and unusable volume, use your hour meter to record the time motored and thru a round numbers mental calculations you may determine at any time how much usable fuel you have left in the tank. As a conservative start point to Burn Rate you can use for 1 Cyl 1/4 GPH, 2 Cyl 1/2 GPH, 3 Cyl 3/4 GPH. Remember the average burn rate only takes into consideration a measure of fuel and time, and no engine, displacement, RPM, hull condition data. ( those may affect how long you travel in an hour but not the Average Burn Rate). Just fill up the tank, record the hour meter reading, drive the boat as you normally do and when you top off the tank again record the amount of gallons taken in as indicated at the pump. Go back to your hour meter and divide the number of gallons by the number of hours and you will have your average burn rate. prepare a log with the hour meter readings, the gallons taken in and the resulting ABR. As you take in your calculations you will be refining your particular ABR by eliminating unusual high and low numbers. There are no exact calculations and believe me the Average calculations based on the way you usually run the boat are more than enough adequate to allow to manage your fuel. in my experience I quite often will predict how much fuel I will need to take at the pump within 1/4 of a gallon. With the ability to calculate fuel left on the fly I can by using GPS speed calculate my range according to conditions on the water. I can calculate if I have fuel to reach my destination or if I need to divert course for refueling. Needles to say my fuel gauge died years ago and I have not even bothered trying to see what is wrong with it. When it was working it would only serve to tell me if I had fuel or not when starting out.

 

[senang]

I record eng hrs at fill up. Every evening New eng hrs - Fill up eng hrs = Tank hours. Knowing hourly diesel burn rate this gives me remaining liters in the tank. Full tank = roughly 40 run hours. So when tank hours appoaches 30, time to fill up.

 

[buddybear]

I record eng hrs at fill up. Every evening New eng hrs - Fill up eng hrs = Tank hours. Knowing hourly diesel burn rate this gives me remaining liters in the tank. Full tank = roughly 40 run hours. So when tank hours appoaches 30, time to fill up.

Have a Catalina 310 #57 Several years ago I replaced the fuel sender with the one from Catalina Direct no issues it reads fairly accurate, you need to know where the gauge is located in the tank. The important thing is to know where the gauge is reading when you are low on fuel, I always try to keep a 1/2 tank.

 

[dLj]

Just to throw some more out there. The best fuel gage with direct readout I've ever had on a boat was a mechanical gage where there was a needle on the top that was run by a spiral piece of flat metal that had a float on it. As the float dropped, the needle moved towards empty. Inaccurate for sure but always with the exact same inaccuracy...

My current boat has a dip stick attached to the tank. I have a wrench mounted next to it so I don't have to go find the right size and I undo the nut holding the dipstick and read my fuel level in similar fashion to reading your oil level in your engine. Pretty direct measure.

All the above said - calculating burn rate is the best method.

dj