Fuel Gauge Issue?

[Bob_A]

Wondering if others have encountered this? We did a fair amount of motoring this past weekend and the fuel gauge doesn't register any fuel used at all.
It does return to zero or empty with the power off and does come to approximately half to 5/8 full with power on as it did when we left and each time the engine was started. All other gauges are working fine.
I'm thinking 10 hours motoring at 1800 to 2000 rpm. Surely it should show a change. I figure we should see a reduction of fuel level of one third from starting out? Thanks in advance.

[Captain Kirk]

Hi Bob

On our boat we have logged our fuel usage for the past 5 seasons, and put on almost 600 hrs on the engine. We're out cruising for 2 to 3 months each season.

What we find is that the fuel gauge works but it is not linear. The top half of the gauge goes from full (after a fill up) to 1/2 full after about 45 or 50 hours. I usually try to fuel up when I'm at 1/2 on the gauge but know I can go safely down to 1/4. However, I have found it only takes approximately 10 hours for the gauge to move from 1/2 down to a 1/4. The last 1/4 of the tank would probably disappear very quickly, but we've rarely gone below 1/4 on the gauge.
We normally cruise around 2300 rpm.

So for 10 hrs at 2000 rpm that you have noted, it could well be hard to discern a level change on the gauge when it's starting 5/8 full. If your gauge is like mine, I would think if you cruised another 10 or 15 hours it would be showing below or close to half full.

[leigh weiss]

The problem as I see it is that the tank is not linear or symmetrical. It is wider on the top few inches and then tapers, The fuel sender appears to be linear, that is one inch of fluid level change corresponds to a linear change of indicated fuel level. My solution to this problem was to empty the tank and then fill it noting the gallons put in to the fuel level indicated. This gives a relative idea as to the remaining fuel in the tank. Make a chart of the results and keep it for reference. The fuel level sending unit might "drift" or change with age as might the gauge. Engine hours and the gauge reading combined are a suggestion of the remaining fuel.
I have not found a better solution but would be happy with one.

Leigh

[Flagmanmike]

Hi BoB and Cherie,

With my Universal M35B, I use about 0.5 gal per hour, so 10 hour is 5 gal. I think the tank is 39 gal, and so I think you should notice a dip on the gage after 10hrs. at mid-tank. Did the gage "wiggle" while moving with the waves or did it stay put at 5/8.
Try removing the fuel gage and make sure the float is free to move. If so, clean the terminals, if no change, then I suggest replacing the gauge. I found a direct replacement on Amazon. Model Sierra 57902P Fuel Gauge Amega 2". It was $23.14 plus tax on Amazon Prime in 2020.

Mike Cronin
FlagShip #314

[Bob_A]

That is great input and advise. I will investigate the gauge.
The non linear relationship between the gauge reading and the tank level makes perfect sense.
I will also begin logging the fuel usage as well.
The PO had indicated a burn rate of 1 gal per hour but Im not sure under what rpm or conditions.
I also suspect it does a bit better than that. The engine runs very well, just under 160 degrees.
I had replaced every fluid, filter and hose associated with the engine plus a new Raw water pump and HE rebuild.
She seems to like it.
Thank-you all.

[wolfe10]

No question, keeping track of diesel fuel level by hours run is a lot more accurate than the linear gauge on a non-linear tank.

.75-1 gallon an hour is pretty close unless you have much time running the engine just to charge the battery (example: in neutral at 1,300 RPM) which takes less fuel.

And, remember, if storing, add a BIOCIDE such as Biobar JF and fill the tank to minimize condensation.

[Bob_A]

Yes absolutely.
Thank-you Brett