Port side fuel gauge "bounces"

[bigdealsam]

I am running between 1/4 and 1/2 tank of fuel in both tanks. The starboard side reads correctly and the gauge is stable. The port side guage continually "bounces" around making the reading somewhat misleading. Any reason the gauge would operate like this? Thanks, sam

 

[Texasmark]

Re: Port side fuel gauge "bounces"

Fuel level sensors are a wire wound resistor and a variable arm (called a rheostat since only 2 terminals used) attached to the float. The bottom of the resistor is grounded at the sending unit and the wiper arm info is sent out the insulated stud on the sending unit to the bottom of the gauge. Top of the gauge goes to switched (ign. key) 12v...purple wire for Mercs.

Empty to full is a change of roughly 35 ohms to 135 or something like that.....I forget the actual resistance and which value is for which.

Anyway, if the otherwise rounded, point contact wiper tip wears significantly, it will become wider and too wide to sit on only one wire of the rheostat at a time. As it vibrates (engine vibes, sloshing fuel, whatever) it will give you one or the other reading.

Best I can do.

Mark

 

[cr2k]

Re: Port side fuel gauge "bounces"

Or it could be aligned so the swing of the float is different from the Starboard side.
Some senders are buffered either mechanically or electronically. The Port tank may not be or has a issue.

 

[Texasmark]

Re: Port side fuel gauge "bounces"

Or it could be aligned so the swing of the float is different from the Starboard side.
Some senders are buffered either mechanically or electronically. The Port tank may not be or has a issue.

That could be it, especially if the boat is relative new and the wipers haven't had time to wear out. However I had a Ford with dual tanks that I used to keep full all the time. This kept the wiper running over the same wire all the time and in less than 3 years it wore through the wire and open circuited.

But, recalling some installations, I think I recall that the holes in the tank/float flange are not symmetrical which would force you to install the sending unit one way. Just don't remember.

Mark