What’s octane? In relatively simple terms, it’s a measure of the fuel’s resistance to premature detonation, or the early ignition of the fuel/air mixture by compression before it would normally be ignited by the firing of the spark plugs in the engine’s combustion chamber. This early ignition of the fuel/air mixture creates a shock wave within the cylinder which collides with the still upwardly moving piston, knocking it against the cylinder walls. The resulting noise is often detected by the operator as a “knock” or “ping” coming from the engine, and over time can cause significant engine damage.
A fuel’s octane rating can be measured in several ways. In the United States and Canada, the most common rating shown on the gas pump is the Anti-Knock Index (AKI), which is the average of the fuel’s Research Octane Number (RON) and Motor Octane Number (MON). This is typically shown at the pump by the abbreviation R+M/2, on a bright yellow label with black lettering. In other countries, the Research Octane Number may be more common.
Your Sea-Doo engine is designed to run most efficiently with fuel of a specific octane rating. For all engines except the 300hp Rotax 1630 ACE - 300, look for unleaded fuel with an AKI (RON+MON)/2 octane rating of 87 (or an RON octane rating of 91). Craft using the high-performance ACE - 300 engine require a higher octane level for best performance, fuel economy and engine life. Use Premium gasoline with an AKI (RON+MON)/2 octane rating of 91 (or an RON octane rating of 95).
These octane requirements can also be found in the Sea-Doo Operator's Guide that comes with each craft.
Try to keep fuel as fresh as possible. Fuel that sits in the tank for prolonged periods can oxidize, lowering the octane level, creating volatile compounds, and producing gum and varnish deposits which may damage the fuel system.
Much of today’s fuel supply is blended with alcohol, specifically ethanol. The maximum amount of ethanol your watercraft can use without problem is 10-percent. Never use fuel labeled E85 (15-percent ethanol). Higher levels of alcohol attract water, less than ideal choice in the marine environment, and can result in starting and operating difficulties, deterioration of rubber and plastic parts, corrosion to metal and damage to internal engine parts.
Always fuel your craft responsibly. If you trailer your watercraft, fuel before you get to the water where the chances of spills are reduced (and the fuel most likely far cheaper than at the marina). Should you fill your craft at home from portable cans, do so in a well-ventilated area.