Choosing the Right Octane for Your Boat’s Engine

The higher the fuel’s octane rating, the less likely it is to prematurely ignite and cause engine knocking. phive2015/Adobe Stock

We see the numbers every day at the local gas station, with gas sold based on octane ratings. Most people go to the lower number—usually 87—because it’s the cheapest, but what do the ratings mean, especially for your boat? First and foremost, the best fuel for your boat is ethanol-free gas, as ethanol scavenges water and causes phase separation, which can gum up your fuel system over time. Without access to that (check with your local marina, where you’ll most likely find it), avoid any gas with over an E10 ethanol mix. Beyond that, a fuel’s octane rating denotes its stability during the ignition phase. The higher the rating, the less likely it is to prematurely ignite and cause engine knocking. Here’s a quick rundown of the different octane ratings.

87

The Burn: The most common gasoline because it’s the least expensive, 87 fuel is fine for most marine outboard and inboard engines. Check your owner’s manual. If your engine requires only 87 gas, spending more on 89 or higher won’t improve your engine’s performance or help you run any faster than it would burning regular 87.

The Knock: While any engine can burn 87 and likely be fine, it can cause knocking in engines that require 91 fuel or higher, which could impede overall performance.

89

The Burn: If your engine experiences knocking from using 87 fuel, jumping up to 89 could solve the problem without resorting to high-performance gasoline, which can cost upwards of a dollar or more per gallon. Consider it a happy medium if 87 isn’t working for you but 91 or higher is overkill for you.

The Knock: With high-performance engines that require 91 gas or higher, 89 will work but still might not be enough to prevent knocking and could impede the engine from optimal running.

Read Next: Portable Fuel Caddies for Boaters

91-Plus

The Burn: High-performance and racing engines, especially those with a turbos or superchargers, create more heat and pressure during operation, which could cause lower-rated gasoline to prematurely ignite and cause knocking and potential engine damage. In some cases, using lower-rated gasoline on an engine that requires a higher-octane rating can even void the warranty, so check your owner’s manual.

The Knock: It’s way more expensive and, if your engine doesn’t need it, offers no benefit to your boat’s performance.

The post Choosing the Right Octane for Your Boat’s Engine appeared first on Boating Mag.