Originally Posted by glassdad
I have a 1985 Catalina 30 with the MX25 diesel. The tank does not hold the full amount of fuel it is supposed to. The tank is stamped that is holds 18 gallons. When i measured it, I calculated its volume at 17.5 gallons.I ran out of fuel about 10 miles out of the harbor. I sailed in , in deteriorating weather, but I would have wanted the engine.
The fuel gauge read full when the tank was full and empty when I ran out. When I filled the tank, it topped out, absolutey full at 12 gallons.
What is causing this. Could I have 6 gallons of sludge in the tank? The fuel looks clean after the the filters and the engine runs good.
Your pick up is NEVER on the dead bottom of the tank and is usually 1" or more off the bottom. This means you will never get the full rated
Sailboats heel and slosh back and forth in a sea thus exposing the pick up to air.. As tanks get low it is very easy to suck air. You may not have been out of fuel but may have very likely sucked air especially if motor sailing..
My rule of thumb is to never let my tank get below 1/3 full to prevent sucking air.
You could also have a low spot/trap in your fuel vent thus causing you to "burp" full early....
Don't EVER count on a boats fuel gauge to be accurate, unless you have specifically calibrated it.
A) Know actual tank volume measure and calculate.
B) Drain tank 100% by removing sender and sucking it 100% dry.
C) Fill in 25% known increments and mark gauge glass
D) Use a Sharpie, paint marker, tape etc. at 25% increments E, 1/4, 1/2, 3/4, F....
E) Now you KNOW the gauge is accurate, but this will still NOT be accurate when heeled....