Hunter fuel monitor

[take.yvr]

Hi,

British Columbia relaxed restrictions set in place to control COVID-19 and residents were allowed to travel within the province, so my wife and I started sailing by our new to us Hunter 306. The fuel monitor showed a full tank and I assumed that the PO filled up the diesel for us, but it was wrong!
The fuel monitor always shows a full tank, regardless of the amount of fuel. I'm lucky I found it before I ran out of gas in the middle of the sea.

The fuel sender looks like a capacitive type since it doesn't have a float. The hunter owner parts store has a replacement sender but I would like to know if the sender is actually bad before placing an order. Please let me know if someone knows how to test the sender.

There are 6 wires coming out of the sender and actually 3 of them (black, red, and blue) are connected to the monitor. The fuel monitor shows full when the sender is connected, but if it's disconnected the monitor shows empty. The monitor is working for a freshwater tank and waste tank.

Thanks!

 

[sail sfbay]

Had the same one on my Hunter 386 and now 46. The following thread might help.

Hunter Tank Monitor

This monitor (picture attached) is original equipment on 2004 Hunter 386LE. It reads full tanks empty and empty tanks full and WILL be replaced. Cursory knowlege (and common since) lead me away from replacing with same and I'm a betting some of you fellas have had similar problems here. If so...

forums.sailboatowners.com

 

[Stu Jackson]

Good on you for finding out, first.
Many recurring posts are questions about fuel gauges of all kinds. Hope you find what you're looking for.

Almost all, if not always all, of these fuel gauge threads include this:
In addition to a fuel gauge, you should, if not MUST, learn what your engine's fuel consumption is. For sailboats it's usually/always gallons per hour. For other boats, usually motor yachts or boats, it's n or inland st miles per gallon. That simply doesn't work for sailboat, see?
For a boat your size, most of us experience around1/2 gallon per hour.

All the best, congratulations on your new boat.

 

[take.yvr]

Thanks sail fsbay for the link. The situation is different but I think it's worth trying to calibrate the sender.

 

[take.yvr]

Thanks, Stu. Yes, PO said the engine consumes 1/2 gallon per hour, so I can calculate how much fuel I still have in the tank. But it's nice if I can double-check it with the monitor (and fixing problems are part of the fun to have a new toy ).

 

[Benny17441]

The sure fire way of knowing how much fuel you have available is to calculate your burn rate (gallons per hour) and keep track of your hours motoring with an hour meter. I assume you have Yanmar 2GM and as a starting point you may use 1/2 Gallon Per Hour. Fill up the tank and start a simple log. Next time you top off the tank write down the date, the number of gallons taken in and the number of hours since last fill. Also include Average Burn Rate by dividing the number of gallons by the number of hours. Recalculating the burn rate at every fill will eventually narrow down a very precise average figure for your particular engine and your way of motoring. The formula does not include the type of boat, the condition of the hull, the actual RPM nor distance travelled as they are irrelevant for this purpose. From your boat's manual figure out the number of gallons your fuel tank holds. Not all the amount of fuel is usable of the capacity of the tank as your engine will start sucking air well before the tank is empty and you would also want to maintain a reserve so calculate and substract 20% from the total figure. The result will be your usable amount of fuel, the point where you will want to refuel once this is expended. It is OK to round figures down to next gallon and up to the next hour so that you can run mental calculations on the fly. Example; you have figured your burn rate at 1/2 GPH and a glance at your hourmeter indicates you have motored 12 hours since last fill so you know you have burned an average of 6 gallons. Your usable fuel capacity is 20 gallons so you can count on having 14 gallons left. Now how far can you go on 14 gallons? Distance is a factor of conditions on the water, you may travel at 6 knots or you may travel at a fraction of just 1 knot. You can calculate range by looking hourly at sustainable speeds in the day of travel. All these information will serve you to estimate how far you can go to your next refueling point or if you need to divert to a closer refueling port. How exact is this method, I usually can predict to approximately 1/4 to 1/2 of a gallon how much fuel the pump meter will indicate I will take to full. I find fuel gauges in boats are highly unreliable and do not provide necessary information to be able to calculate range.

 

[buddy0]

I think this is what I have on my 2005 Hunter 33. Here is my thread and solution:

6 wire fuel sending unit - what is this?

Just when I thought I had fuel sending units figured out, I come across this in my 2005 Hunter 33-2. Not sure how to test it or what to replace it with. There are 3 wires coming into the connector from the boat and 6 wires coming from the sending unit. There are 0 ohms between two of the six...

forums.sailboatowners.com

In summary I replaced the sending unit with a common resistance based sensor and soldered a 510 ohm resistor between the power and sensor wires.

 

[take.yvr]

Benny, thanks for the detailed calculation method. I'll start logging the fuel consumption from the next fill up (That's my first fill up and that makes me nervous...).
As you mentioned, what I'm afraid of is the engine sucks air and needs bleeding the air in the middle of the busy waterway. I'll try to maintain 20% of the fule to avoid it.

 

[sail sfbay]

...............As you mentioned, what I'm afraid of is the engine sucks air and needs bleeding the air in the middle of the busy waterway. I'll try to maintain 20% of the fule to avoid it.

Suggest keeping your fuel tank topped off to mitigate algae formation and fuel filter plugging. Once you have some run time and determine fuel consumption then you can schedule your fuel filling cycle. I use two, easy to manage 2.5 gallon containers with a self closing nozzle for this purpose.

 

[take.yvr]

Bubby0, it looks like you had the same problem. I couldn't find your thread when I searched the forum. Anyway, thanks for pointing out it to me.
In your photos, I see that the green and red LEDs are lit, are they always on when the sender is connected? Or they're on when the monitor sends the voltage? My sender LEDs were always off when I checked.

 

[take.yvr]

Sail sfbay, thanks for the tips!

 

[Stu Jackson]

Benny, thanks for the detailed calculation method.

Benny's right, here's mine, click on the attachment PDF for the picture of my spreadsheet:

Fuel Log 101

Fuel Log

 

[buddy0]

I never saw the green and red LEDs lit on the fuel sending unit in my case. They look like they are lit in the photo, but they really are not. It must be from the flash or the sun.

-buddy

 

[take.yvr]

Hi Stu, yes, I was thinking to create the same kind of table. Thanks for the information.

 

[take.yvr]

I see Bubby. Thanks!

 

[take.yvr]

The diesel tank monitor/sender issue finally resolved.

First, I calibrated the tank monitor based on the Snake River monitor calibration guide attached in the following thread.
Hunter Tank Monitor
The monitor calibration showed a sign of improvement. The tank monitor indicated half full when the tank was full and empty when the tank was empty.
Then I found the attached document which instructs how to calibrate the fuel sender.
After calibrating both the fuel sender and tank monitor, the monitor shows the correct fuel level.

I also started logging the fuel consumption (gallons per hour) as Stu suggested so that I can estimate the fuel level even if the tank monitor breaks down again.

Thanks all for helping this out.