Catalina 350 International Association

I suspect our fuel sending unit has gone bad. One minute it seemed to be reading correctly between 3/4 full and full then a short time later I noticed the gauge was reading FULL. Either we are producing fuel as we motor along, or the sender, gauge, or wiring has become faulty. Can anyone offer a suggestion as to how I can determine whether it is the sending unit, the gauge, or a wiring problem? Our sending unit is labeled WEMA SSS 10. If that is the culprit, any ideas as to where we can buy one?

Thanks

Gary, Sail Magazine has a very good article showing the procedure to test the gauge, sending unit and wiring. http://www.sailmagazine.com/diy/engines ... ding-unit/

I had to replace my sending unit a couple of years ago following a lightening strike and ended up purchasing it here - http://www.duskyonline.com/WEMA-p-fuel- ... prod-chart. A google search shows that a number of merchants carry this unit.

Thanks Ken,

How do you know all of this stuff?

The link for the Sail Mag article did not work, but I found my way there. The correct link is http://www.sailmagazine.com/diy/engines ... ding-unit/
It clearly describes how to check the gauge. There doesn't seem to be any real method to test the sending unit, just if the gauge is good and the wire is good, then it must be the sending unit.

Thanks again for all the work you do on this site. You certainly make sailing more fun for all of us.

We tested our fuel sending unit by removing the sending unit from the tank and as I raised and lowered the collar from the top (full) to the bottom (empty) the Admiral would call out what the gauge was showing.

The unit was fine but I realized since the tank is not square when the gauge shows 3/4 you are probably 2/3. At 1/2 on the gauge you are probably 1/3, etc.

KevinMc wrote: The unit was fine but I realized since the tank is not square when the gauge shows 3/4 you are probably 2/3. At 1/2 on the gauge you are probably 1/3, etc.

CORRECT! No linear gauge will accurately report real fuel quantity with the shape of the tank. "Owner extrapolation" is needed.
At 1/2 on the gauge, it is time to refill.

Also, remember that you have a high bypass fuel system-- much more fuel is pumped to the engine than is consumed. The "excess" returns to the tank. This aids in cooling and lubricating the fuel injection components. After you have run for a couple of hours, raise the bed and feel the temperature of the tank. Bottom line, particularly in warm conditions, the fuller the tank, the cooler the fuel will be to the engine. And cool fuel is better than hot fuel.

KevinMc wrote:We tested our fuel sending unit by removing the sending unit from the tank and as I raised and lowered the collar from the top (full) to the bottom (empty) the Admiral would call out what the gauge was showing.

I like this approach. Reading the article from Sail Mag, the approach is to test the gauge, and then test the wire. If both are good, then by default the sending unit must be bad. The problem I see with this approach is that I believe the sending unit is hard wired (no removable connection). That means in order to test the wire, you would have to cut it to check it's resistance. Of course that isn't a big problem as if the gauge is good either the wire or the sending unit needs to be replaced, and both would require cutting the wire. But I like the non-destructive test approach much better, and it would also be much quicker. That's my plan for today.