[C320-list] Fuel Gauge Stuck on Full

[Chris Burti]

*A common problem* In this case the gauge is a voltmeter and the float
mechanism in the tank is essentially a variable resistor. Voltage goes to
the tank sender, if the tank is full the circuit is almost open and the
gauge reads full. As the float drops, resistance increases, and the needle
drops correspondingly.

If the problem is with the sender, it can be tested by removing the shelf in
the starboard aft locker and removing all wires. Tested with an ohm meter it
should read between 60 and 120 ohms. Open or closed circuit readings
indicate a failure of the unit.

If that checks out and, as it sounds like from your description, the gauge
reads 'full' when not working, there may be a short in the circuit.
If the gauge reads 'empty' when not working, there may be a broken wire.

If the sender is good and the wiring is good, that just leaves the gauge to
be bad. You open the engine pod to do all this testing, disconnect the pink
power lead from the gauge, it should then read "empty". If not, it is bad.
If it does read "empty", jump the power lead from the lights to the terminal
for the tank lead (pink) and the gauge will read 'full' when you turn the
key on. Run a jumper from the tank to the gauge, if it reads correctly, you
have a short in your sending wire (the most common problem according to the
techie at Seaward"

On Mon, Mar 31, 2008 at 9:44 AM, Jeff Hare <catalina at thehares.com> wrote:

> Hi Bruce,
>
>  Actually, the fuel gauge circuit is very simple.  The fuel sender is
> simply a variable resistor.  That's all.
> Annie's correct about the fuel sender arm.
>
> 1) If it were installed incorrectly (rotated 90 degrees like mine was) it
> would not be stuck on full, instead the gauge would not be able to reach
> full.
> 2) If it ever worked properly, then it was installed correctly, so ignore
> #1
> 3) If it stopped working suddenly and is stuck either on full or empty,
> then
> this may indicate *either* a short or an open circuit, and I don't recall
> if
> a "short circuit" causes the gauge to read full or empty.
>
> * First, check the top of the tank where the fuel hoses enter and verify
> that the wires connecting to the tank sender are in good shape.
> * Next, remove the wheel and open the engine pod, and find the fuel gauge.
> * Ensure that the connections are in good shape.
> * Follow the sender wire(s) from the back of the gauge to the "terminal
> block" (where the wires come up through the tube from below).
> * Frequently this junction block is a problem.  I had loose wires, and
> other
> wires that were clamped on insulation not bare wire.
>
> Seaward provides the tanks and gauges for Catalina and they gave me a
> procedure for diagnosing the gauge many years back.  I don't have it
> anymore.  Perhaps someone can find the procedure from Seaward and send it
> to
> you, or I'll look for it if nobody steps up.
>
> On the back of the gauge, there is a power wire and a ground wire (maybe
> connected to the frames of all the gauges.)  This powers the backlighting
> of
> the gauges.  There will be 1 or 2 other wires connected to the back of the
> gauge, they go to the sender on the fuel tank.  Disconnect one of them and
> then see if the gauge goes to Empty.  If it does, then it indicates (I
> believe) that you probably have either bad sender.
>
> Replacing the sender is not a big deal, but here are a few tips:
>
> 1) Try not to do this with a full tank!  The emptier the better as you'll
> be
> able to diagnose whether it's really fixed or not.
>
> 2) Important:  Before Removing the plate on the top of the tank holding
> the
> sender, take a black marker and make a mark on orientation of the plate
> and
> the top of the fuel tank so that you get it oriented the same way during
> reassembly.  It only fits ONE way.  Any other orientation, you'll won't be
> able to get all 5 screws to align with their holes.  Close, but not quite.
> Took me a while to figure out that the holes weren't symmetrically placed,
> presumably to ensure that the sender goes in properly.
>
> 3) Use a Phillips screwdriver bit on a socket wrench to give you 90
> degrees
> access to the screws holding the cover and it's Easy.  Try a regular
> screwdriver and you'll fight with it.  Don't lose the screws!
>
> 4) Note the direction that the sender arm swings when removing it.
>
> 5) Keep some rags nearby to protect against drips, clean the seal really
> well before putting it back together.
>
> -Jeff
>
>
>
>
> -----Original Message-----
> From: c320-list-bounces at lists.catalina320.com
> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Bruce
> Stanley
> Sent: Sunday, March 30, 2008 6:42 PM
> To: C320-List
> Subject: [C320-list] Fuel Gauge Stuck on Full
>
> The Fuel Gauge is Stuck on Full ... when it was 3/4 empty!
>
> any thoughts on fixing this the problem?
>
> thanks
> Bruce Stanley #1084/FantasticLady/Sydney Australia
>
>


-- 
Chris Burti
Farmville, NC