Fuel Sending Unit

[KenKrawford]

Does anyone know a source or the specs. for the fuel sender? I know it's supposed to be 33 to 240 OHMS RESISTANCE but am unsure about the depth of the tank.
Thanks.

[djones]

Hello Ken,
Please go over to the "engine" section, and look up my earlier post: "fuel tank level sensor". It will give you the info you need I believe.

Thanks,
Don Jones
C350 #13 Onatop
Oak Island / Southport NC

[KenKrawford]

Thanks for the info Don. My sender is labeled WEMA 10. I wonder if they changed this in later hull #'s (I have 351) or do I still have a fair amount of fuel left when my gauge reads empty? Do you recall the model # of your original sender?

[djones]

Ken,
I'm sorry, but I don't remember the original model number. But that is where I got in trouble! The old model # was no longer made by Wema, but it was the 12" size, so I ordered the "exact" replacement of the newer version. That newer version while also being a 12" model, was actually slightly longer than the original, and hit the bottom of the tank.

That's why I went with the unit one size shorter (11.5"). Suggest you pull yours out, and measure from the top of the mounting hole flange to the bottom of the tank.

I think I still have the brand-new 12" sensor that was slightly too long for my tank. Might work in yours depending on the true depth of your tank.

Thanks,
Don

[wolfe10]

Kind of off topic, but I have always kept track of engine hours to gauge fuel usage. Since the tank is NOT straight sided, the gauge is not and can not be linear.

And, as a side issue, all diesels are HIGH BYPASS engines-- for every gallon of fuel pumped to the engine, they burn perhaps and ounce or two. The rest is used to cool and lubricate the injection system (and head on some models). Run low on fuel and reach under and feel the fuel tank. It will be HOT. Not good for the injection system.

Brett

[KenKrawford]

I pulled out the fuel sending unit (labeled SSS 10 indicating it is 10" long). My tank measures 11 1/2" deep. WEMA tech support recommends that the sender be 1" shorter than the depth of the tank so I replaced with a 10 1/2" unit.

[KevinMc]

Do other C350 owners somewhat agree with my guesstimate below?

I've noticed the fuel gauge has always seemed to be reading higher than it should be. Reading the posts I suspected the fuel sensor was an old style and needed replacement. Removing the sensor this weekend I was pleasantly surprised to see it is the modern version and is working fine. (Fuel sensor float at the top = fuel gauge shows full, 3/4 = 3/4 full at gauge, etc.) I suspect the sensor is not calibrated for the shape of the tank and the various tank angles are causing the higher readings I'm getting.

Eyeballing the tank shape online at Catalina Direct I'm guessing:
Gauge showing full = full tank
Gauge showing 3/4 = 2/3 remaining fuel
Gauge showing 1/2 = 1/3 remaining fuel
Gauge showing 1/4 = better be at the fuel pier since you have a few gallons remaining and the fuel pickup is probably an inch off the bottom of the tank anyway.

Thoughts?

[leigh weiss]

Great observations.
It seems to me that the sending unit is a linear device working in a non linear environment ( shape of the tank and angle of boat)
Our expectations might be bases on our car gauges and tanks, which are relatively linear.
I have used my fuel gauge as a relative guide to remind me when to top up. The hour meter is as good an indicator of fuel usage as the gauge.
Keeping notes on refueling quantities and starting gauge position provides a quick corrected reference when the boat is level.
I don't know of any better system for fuel level indication but would be interested in any alternatives.