Fuel gauge always reads full

[pbyrne]

The fuel gauge always reads full, but drops to empty when power is switched off.  After 3 hours of motoring it didn't budge, and when I fueled up the boat took 42L (11 Gallons). 

I have no idea where to start looking to fix this.  Suggestions?

[Jim Hardesty]

It's a lot of reading and information but do a search for "fuel gage".  Somewhere here is instructions for checking the fuel level sensor I think.  It's a float, lever and rheostat, very low teck.  Hardest part of checking it is emptying cockpit locker. Need a multimeter. Shamrocks was bad when I first got her, bought a generic one from local marine store, has worked for many years.
Honestly, I don't depend on the fuel gage much.  I use the hour meter.  Shamrock usually burns a little less than .7 gallons per hour.  Multiply .7 by hours since last fill up gives me the gallons to fill up.  Find your own burn rate by keeping a log of fuel use divided by engine hours. ie.  gallons per hour or g/h
Jim

[pbyrne]

It's a lot of reading and information but do a search for "fuel gage".  Somewhere here is instructions for checking the fuel level sensor I think.  It's a float, lever and rheostat, very low teck.  Hardest part of checking it is emptying cockpit locker. Need a multimeter. Shamrocks was bad when I first got her, bought a generic one from local marine store, has worked for many years.
Honestly, I don't depend on the fuel gage much.  I use the hour meter.  Shamrock usually burns a little less than .7 gallons per hour.  Multiply .7 by hours since last fill up gives me the gallons to fill up.  Find your own burn rate by keeping a log of fuel use divided by engine hours. ie.  gallons per hour or g/h
Jim

Ok Will do.  The gauge itself seems ok as it responds to power, and considering your desription it makes me think it's failed shorted so to speak. 

Could you suggest what is a suitable replacement part?   This is a new area for me!

[Ron Hill]

pby : It sounds like your float machoism "Ist Kaput"!  Look in the Mainsheet tech notes for my Mainsheet article on replacing the fuel float switch. There a ton of stuff in WiKi about the fuel gage and float system. 

Also remember that the fuel tank is asymmetrical so you will NEVER have an exact accurate float gage reading.   

Do as Jim suggests and use the clock and fuel consumption rather than the gage.

A few thoughts

[KWKloeber]

In this order:

1) Check the gauge -- I had put the Teleflex gauge technical/troubleshooting guide on the Wiki; in the engine section.

     If the gauge checks out Ok then:

2) Remove the sender wire from the tank float -- the gauge should bottom out below Empty.  Ground the sender wire to a known good ground -- the gauge should pin above Full.

     If the gauge doesn't respond correctly then:

3) The problem could be that the sender wire is shorted to ground somewhere -- check the harness.

     If the gauge responds correctly then:

4) Remove the fuel level sender to check it's action and whether it is shorted-out and needs replacing.

[Noah]

Once you get that sorted...be aware that due to our tanks NOT being square, the gauge is only "correct" when it reads 100% full and 100% empty.😎

[Breakin Away]

Once you get that sorted...be aware that due to our tanks NOT being square, the gauge is only "correct" when it reads 100% full and 100% empty.😎

Actually mine is not even correct at those points either...

[pbyrne]

In this order:

1) Check the gauge -- I had put the Teleflex gauge technical/troubleshooting guide on the Wiki; in the engine section.

     If the gauge checks out Ok then:

2) Remove the sender wire from the tank float -- the gauge should bottom out below Empty.  Ground the sender wire to a known good ground -- the gauge should pin above Full.

     If the gauge doesn't respond correctly then:

3) The problem could be that the sender wire is shorted to ground somewhere -- check the harness.

     If the gauge responds correctly then:

4) Remove the fuel level sender to check it's action and whether it is shorted-out and needs replacing.

Excellent! Thank you, fix by numbers is perfect for me. 

[pbyrne]

Once you get that sorted...be aware that due to our tanks NOT being square, the gauge is only "correct" when it reads 100% full and 100% empty.😎

LOL Noted!

[pbyrne]

pby : It sounds like your float machoism "Ist Kaput"!  Look in the Mainsheet tech notes for my Mainsheet article on replacing the fuel float switch. There a ton of stuff in WiKi about the fuel gage and float system. 

Also remember that the fuel tank is asymmetrical so you will NEVER have an exact accurate float gage reading.   

Do as Jim suggests and use the clock and fuel consumption rather than the gage.

A few thoughts

Thank you! I will look it up.  Do you know where I could order a new one from?  Sounds like I might need one..

[pbyrne]

https://www.catalinadirect.com/shop-by-boat/catalina-36/engine/instruments/fuel-tank-sending-unit-12quot-stainless-c-34-c-36-25-gal-tank/

Does that look right?

[Ron Hill]

pby : My article gives you step by step how too - starting with what you need to remove to get things done!!  With a picture!!
You can get replacement fuel float gage mechanisms from Defender, West Marine etc at a much lower cost $$ than Catalina Direct!!

A few thoughts

[pbyrne]

pby : My article gives you step by step how too - starting with what you need to remove to get things done!!  With a picture!!
You can get replacement fuel float gage mechanisms from Defender, West Marine etc at a much lower cost $$ than Catalina Direct!!

A few thoughts

Is this it?

[Ron Hill]

pby : Yes, that article talks about BOTH the sender replacement and cleaning the in side of the fuel tank.  Mainsheet Nov. 2003

A thought

[pbyrne]

I'm not at the boat to check, but would the 12" sender listed here but the correct replacement?

https://www.marineoutfitters.ca/index.cfm?category=10025|10273&product=75153522&code=739729000038