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» Presentation - Winter lay up - fill but do not over fill

When winterizing your boat do not over fill the fuel tank
With the proliferation of E10 gasoline, a mixture of 90% petroleum and 10% ethanol, there has been a lot of discussion on the issue of phase separation during the winter lay up.

Phase separation is caused when water enters the fuel tank and causes the ethanol to separate from the petroleum and absorb the water. This leaves the tank with a lower layer with a mixture of mostly high octane ethanol and some water and a upper layer of low octane petroleum fuel. Both of these can cause various problem.

The answer that I have read on various message boards is to fill the fuel tank to the very top. The reasoning is by toping off the tank so its full to the very top you will prevent air from being in the tank. By preventing air from being in the tank you will prevent condensation from forming in the tank and this will prevent water from getting into your fuel, thus preventing phase separation.

OK, here is the question:

Your boat has a 200 gallon tank.
The tank is near full.
Its been 30 degrees F for several days so by now your gas is at 30 degrees.
You top off the tank so it's full. Spring comes. The temperature rises to over 70 degrees for several days.
This causes your fuel temperature to rise to 70 degrees.
How much gasoline will overflow and spill out onto the ground?

Answer: 5.52 gallons will spill out on the ground.

The "coefficient of expansion." Called the API factor for gasoline is .00069/degreeF Total Temperature change was 40 degrees
200 (gallons) * 40 (temperature change in degrees F) * API factor .00069 = 5.52 gallons

I suggest you do fill your tank but do not top it off. Leave some room for fuel expansion.

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