Mercury Jet 65 Manual page 26

FUEL AND OIL
Remove portable fuel tanks from boat to refill them.
Always stop engine before refilling tanks.
Do not completely fill the fuel tanks. Leave approximately 10% of the tank volume unfilled. Fuel will expand in
volume as its temperature rises and can leak under pressure if the tank is completely filled.
PORTABLE FUEL TANK PLACEMENT IN THE BOAT
Place the fuel tank in the boat so the vent is higher than the fuel level under normal boat operating conditions.
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