Other items that can help reduce vapor locking are: Increasing engine compartment ventilation to move the hot air out of it during a ‘heat soak’ will decrease vapor locking. Under the hottest outside air temperature condition that the boat will be operated in, the maximum air temperature inside the engine compartment, measured at the flame arrestor, shall not exceed 176 o F (80 o C).Ĭ. Mercury MerCruiser engine compartment air temperature specification that became effective Januis: This greatly increases the chances of vapor locking.ī. The highest air temperatures during a ‘heat soak’ will occur 30-40 minutes after the engine is shut off and can stay at that peak for up to 1-1/2 hours. Normally, the quieter the engine compartment is, the hotter the air tempera ture will be on the inside during the ‘heat soak’. This is because there is no air movement inside the compartment and no coolant flow through the engine. The air temperature inside the engine compartment during a ‘heat soak’ will rise higher than during the engine’s ‘running time’. This period of time is called the ‘heat soak’ time. This can cause high air temperature inside the engine compartment while the engine is operating and for a period of time after it is shut off. This is done by using an insulation material and by making ‘engine covers’ tighter. Over the last several years, engine compartments have been designed to be quieter. Fuels purchased in most areas of the USA from late September through early April will cause most of the problems.Ī. Refilling the boat’s fuel tank with lower RVP fuel will decrease the chance of vapor locking. 11 to 15 RVP (cool to cold weather) fuel will change from liquid to a vapor at lower fuel temperature than 8 to 10 RVP (warm to hot weather) fuel will. Find out what the RVP of the fuel in the boat’s fuel tank is. Fuels containing alcohol are more likely to vapor lock on hot days.ī. Find out what type of fuel is in the boat’s fuel tank. If these more common problems are not causing the complaint, then continue.Ī. Use a portable outboard fuel tank con nected directly to the engine’s fuel inlet fitting as a quick way to test the system. Include the brass fitting threaded into the engine’s inlet in this test. Always use a wrench to hold a brass fitting that is threaded into an alumi num casting when tightening another fitting threaded into it to prevent the casting from cracking.Ĭheck the complete fuel supply system of the boat for a fuel restriction. Often systems will leak air but not fuel. Pressurize the fuel system that goes to the en gine to 8 psi (55 kPa) with a hand pump to see if it holds this pressure. IMPORTANT: Do not pressurize the boat’s fuel tank(s) in this test.ĭisconnect the fuel line from fuel tank(s). Check for a cracked housing where a brass fuel fitting is threaded in it. Check the tightness of all fuel fittings and clamps.
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