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Fuel Gage Repairs

The fuel gage on SilverSwan always was on "E" even when the the boat was winterized. It is customary to fill the fuel system  to remove as much of the air space to reduce the moisture entrapment . The normal expansion and contraction of the air cavity will bring moisture with it. I did not know if the problem was in the display or the float sending unit. I chose to replace both units with the display being first, after all it was the easiest to replace. It looked good but still read "E".  Don Walters who had purchased a new Catalina 28 commented that his gage always read "F" even when he had to be towed back to the dock. His sending unit was installed so that the float was jammed on the tank wall. This started a short debate on what was better always displaying "E" or "F". We decided it was a tie.

Inside view of sender location The fuel tank was placed behind the engine on a plywood  shelf secured in place by a couple mounting straps. Each strap had 2 phillips head screws securing the end. Between the strap and the tank was a elastomeric layer to prevent wear and to reduce possible noise. The only way to reach the screws would be the following:
    1) Disconnect the engine, slide it forward out of the way  for direct access. Slide the tank from the shelf to gain adequate clearance to remove the sending unit.

    2) Remove the small side panels in the laserette and crawl in head first. Try to reach the mounting screws and lift, scoot the tank  when freed to the laserette so that the top of the tank has vertical room to remove the sending unit.

    3) Forget fixing the fuel unit and always carry a jerry can of diesel and get good at bleeding the air out of the fuel line.( A real pain and takes about 10 minutes)

    4) Don't move the engine, don't move the fuel tank, just cut a hole in the cockpit floor directly over top the fuel sending unit.


Outside view of sender location through access port
I would have to assume that the sending unit was the original one. I do not think that the fuel tank had ever been moved. I decided that the only was to replace the sending unit was  option 4 especially due to the tank being full of fuel. I did not know this for fact, but it is a logical part of winterizing. WIth a long stick, I measured the location of the sending unit from the edge of the hatch by using a plumb bob. Then I moved the stick to the hatch and used the plumb bob to drop the position to the bottom of the cockpit floor. The tank is off center by 3 inches due to the water lift hose and muffler so I guessed where the sender should be. The stainless steel access port that I chose was from West Marine. It has a 5 inch opening which allows for some positional error. To minimize the error, I drilled a small hole where I believed the sending unit to be and dropped a rod down to check. I was 1/2 inch off and it was close enough for me. The required hole was transferred to the floor, the inside surface checked again for wires or other important things and then cut out with a jig saw.  If you have wires in the way, you can break the saw blade so that it just pokes its way through the material that you are cutting. The floor is balsa cored, so it is a wise idea to mix a little epoxy and seal the wood to prevent future problems.  I snapped a pic of the core for your reference. Its over 3/4" almost 7/8" thick total. balsa corereplacement gage





















The top of the tank is right there just a few inches of clearance. The sending unit was installed with self tapping hex head screws. The flange was sealed with a cork gasket and a liquid sealer.  The mounting flange is suppose to be a standard size with a standard bolt pattern. You may have to pry the old flange loose, I used a wood chisel to free mine and then remove the gasket. My suppositions were correct the fuel level was 1/2 inch from the top. I had run the engine for an hour while cruising around and several hours at mid speed at the dock to charge the batteries.
 The new sending unit was a different design and manufacture but it should fit. I quickly discovered that the mounting hole pattern was  directional , the spacing of the 5 holes was not even. I had to disassemble the flange and discover the proper orientation. The float arm was then re-assembled for me to discover the direction that I wanted the float to sit was impossible because the tank has a baffle plate in the way. I chose plan "B" and chose a rear corner on port side to target the float arm to.  After a couple of small bends the float arm  reached the corner without rubbing on the tank walls. The new unit has an elastomeric sealing gasket with a stainless steel staple in it to connect the sending unit electrically to the tank. The screws have a sealant placed under the heads to ensure that the mounting holes do not leak.

Now was the time to verify that it wasn't a broke wire of other problem. The power was turned on and the gage read "F".   The old sending unit's winding had become an open circuit. It is suppose to change from  35 to 240 ohms to vary the current that the display needs to move the needle.Schematic

The stainless steel access port was installed with Silicone sealant. I like the stuff because it remains flexible. The cover plate was installed with a spanner wrench. When checked a week later for leaks, none were detected.  I checked the sending units screws and a few were a little loose. The gasket will take a compression set and the screws can be retightened to ensure a good seal. Don't over tighten and strip the threads or extrude the gasket.

Should the sending unit ever act up again , the project will be quite simple.

Update: At 1/4 tank reading on the gage, I ran out of fuel. This was confirmed by viewing the sediment bowl in the aux fuel filter. I kept 3 gallons of diesel on board just for this purpose.

I wanted to find out where "E" really was. Back at the dock, I bend the sending unit's shaft with a "Z" bend to shorten it up. I did this several times until it read at 1/4 tank. I then proceded to fill the tank to a total of 10 gallons and it was 1/2 inch from the top and read " FULL". I now know that I have a usuable range from FULL to 1/4 tank with fuel to spare. I will still carry 3 gallons of spare fuel. The local marinas only carry gas.
Fuel consumption was 37 hrs of run time on 11 gallons, or about 3.4 hrs per gallon. With a cruising speed of 6 knots, that would equate to 20 nautical miles per gallon, or a total range of 200 nautical miles.

9-30-04