SmartCraft Fuel Level Gauge Setup Issue

[rpr]

Verado serial number is in my sig.

I can’t seem to get my SmartCraft SC1000/SC100 fuel gauge calibrated right. I’m using the default calibration option, programming in my 57 gallon fuel tank capacity, and with my tank full my gauge still only reads 58% or 37 gallons. It shows empty when I get down to about a 1/2 full tank.

I see a couple of old threads with similar issues but no resolution was ever posted.

There were a lot of issues with this rig when I first took delivery of it new 3 years ago, so I suppose it’s possible that the harness wasn’t connected correctly. I did a Master Reset on the SmartCraft and got the same results after calibrating again using the default setting and programming in a 57 gallon capacity tank.

Any ideas what the issue might be?

[rpr]

Quick updates.

I’ve confirmed the sender is wired correctly to the SmartCraft harness (still using the stock analog sender, it’s still connected to the green ground wire in the analog harness, and the pink sender wire from the analog harness has been replaced with the pink/black stripe sender wire from the SmartCraft harness).

I have a Rochester 9800 fuel sender. Specs show 30 ohms when full and 240 ohms when empty. I’m getting 64 ohms (at full). The gauge drops empty and gives me a low fuel warning when I still have ~30 gallons in the tank.

My tank is bulbous in the area where the sender is mounted, and the sender is not flat (might be at a 5 degree angle). I’m not sure if the tank was manufactured this way or if it expanded. It does build up a ridiculous amount of pressure on occasion. Quite a bit of venting when I pop the gas cap.

The full reading could potentially be affected by the top of the tank “lifting” at an angle in the area where the sensor is. I can see there’s approx. 2” from the fuel level to the height of the sender in this area while the fuel level is right up against the top of the ends of the tank. However, while that could affect the full reading (which a Custom SmartCraft fuel tank calibration might correct) this should not result in an empty reading with 30 gallons still in the tank (which I’m also getting despite multiple Default SmartCraft fuel tank calibrations). Unless Triton cut the fuel float arm way too short when they installed it.

Most likely a bad sender? Are there any other tests I can do on it that I’m overlooking?

[EuropeanAM]

Sender would be my suspect.

[Pulsare2020]

I would tend to suspect the sending unit as well. If your sending unit was installed in the front of the tank and the top has bulged out due to pressure it could read very low at a half a tank. If the sending unit is near the rear of the tank (like mine) it would tend to read more fuel than you really have and that is why mine reads full until I get between 1/2 - 3/4 tank. I just drew the diagrams on xl and tilted the tank +6* and -6*. The sending unit should really be in the center of the tank to eliminate this level error but then you need an access plate in the floor to get to it.

[rpr]

Thought I would provide an update for anyone else with similar issues.

The fuel sender checked out fine, the ohm readings were perfect with the float in the bottom and top positions.

I talked to the manufacturer of my tank and they said the poly tanks on these closed systems will typically permanently deform to some degree from the built up pressure and bulge. They felt like mine might be borderline excessive though. My 9” deep tank is now close to 11” deep. They were also under the impression that at some point the fuel cap is supposed to vent excessive built up pressure, so it’s possible my Attwood cap might be faulty. It’s definitely allowing air in as I have no fuel flow issues, but it’s tough to tell if it’s venting excessive pressure. It’s also possible that the carbon canister venting system is not working properly.

The manufacturer of the poly tank said when they expand, they generally stay in that expanded shape and do not contract back to the original shape. So I’ve ordered a 9 1/2” sender to replace my 8 1/2” one (that will still allow the bottom of the sender to sit 1”+ above the bottom of the tank).

I would feel better if I confirm the fuel cap and/or carbon canister system are venting properly but I’m not really sure how to accomplish that.

[MichaelJ3]

Thought I would provide an update for anyone else with similar issues.

The fuel sender checked out fine, the ohm readings were perfect with the float in the bottom and top positions.

I talked to the manufacturer of my tank and they said the poly tanks on these closed systems will typically permanently deform to some degree from the built up pressure and bulge. They felt like mine might be borderline excessive though. My 9” deep tank is now close to 11” deep. They were also under the impression that at some point the fuel cap is supposed to vent excessive built up pressure, so it’s possible my Attwood cap might be faulty. It’s definitely allowing air in as I have no fuel flow issues, but it’s tough to tell if it’s venting excessive pressure. It’s also possible that the carbon canister venting system is not working properly.

The manufacturer of the poly tank said when they expand, they generally stay in that expanded shape and do not contract back to the original shape. So I’ve ordered a 9 1/2” sender to replace my 8 1/2” one (that will still allow the bottom of the sender to sit 1”+ above the bottom of the tank).

I would feel better if I confirm the fuel cap and/or carbon canister system are venting properly but I’m not really sure how to accomplish that.

I'd still recommend the "Fuel used" method mentioned above...even after a sender replace.

[rpr]

Yes, I’m planning on using the “Fuel Used” for more accurate fuel level readings, but I would like to be able to glance at my SC100 fuel gauge and it at least give me a rough idea as to where I am (better than empty at 1/2 full).

[EuropeanAM]

Thought I would provide an update for anyone else with similar issues.

The fuel sender checked out fine, the ohm readings were perfect with the float in the bottom and top positions.

I talked to the manufacturer of my tank and they said the poly tanks on these closed systems will typically permanently deform to some degree from the built up pressure and bulge. They felt like mine might be borderline excessive though. My 9” deep tank is now close to 11” deep. They were also under the impression that at some point the fuel cap is supposed to vent excessive built up pressure, so it’s possible my Attwood cap might be faulty. It’s definitely allowing air in as I have no fuel flow issues, but it’s tough to tell if it’s venting excessive pressure. It’s also possible that the carbon canister venting system is not working properly.

The manufacturer of the poly tank said when they expand, they generally stay in that expanded shape and do not contract back to the original shape. So I’ve ordered a 9 1/2” sender to replace my 8 1/2” one (that will still allow the bottom of the sender to sit 1”+ above the bottom of the tank).

I would feel better if I confirm the fuel cap and/or carbon canister system are venting properly but I’m not really sure how to accomplish that.

This is about the best suggestion. Caps/systems must hold a minimum pressure (but I don't recall seeing a maximum spec at this particular point). MUST be able to hold 5psi without venting outward into the atmosphere.

Poly tanks aren't the only ones that "permanently" change shape. They are definitely more likely to, though.

[rpr]

I installed the longer fuel sender due to the tank expansion and did a custom SmartCraft fuel gauge calibration and all is well. I did not do the custom SmartCraft calibration by emptying and filling the tank. Since my tank is rectangular (or at least it was before it expanded) I did the custom calibration with the sender connected but not mounted on the tank, placing the float in the positions that correlate to 1/4, 1/2 and 3/4 full, offsetting those positions by 1” as the float still sits about 1” below the top of the sender due to the degree to which the top of the tank has ballooned on me. I then installed the sender for the final “Full” position since the tank was full at the time. A bit more complicated than I expected due to the effects of the top and bottom of the tank ballooning.

I also noted that the tank was labeled a 63 gallon tank, even though Triton lists the tank on this boat as being a 57 gallon tank. I called the tank manufacturer about this (Dometic) and they said this tank was originally manufactured by a different company and when they took ownership of it they determined it actually had a capacity of 63 gallons. It’s probably significantly more than that now due to the ballooning. So I really didn’t know what capacity to program in to SmartCraft gauges. I used 62 gallons to be conservative.

At the very least, I’ll get more meaningful fuel level readings now on the SmartCraft gauges that will at least provide some relative value. It’s amazing how much they were affected by the tank expansion (showing 3/4 when full, and showing empty when still 1/2 full).

My 57-gallon capacity tank might actually now be a 70-gallon capacity tank due to the incorrect spec from Triton and the expansion/ballooning.

These gremlins have reinforced the “assume nothing” perspective of my boat ownership odysseys…

[EuropeanAM]

Just be VERY careful when doing this type of "cheat" method. If the EMPTY position is too low, an you've added length to the sender, it's potentially possible to run out of fuel and "think" you have fuel remaining.

Remember that the pickup tube is not flush on the bottom of the tank... so we usually make the EMPTY position no less than 10% fluid capacity.

[rpr]

Wise words of caution, thanks. My longer sender still sits 1”+ off the bottom of the tank, but I definitely don’t plan to push my luck when levels get below 1/4 full.