The Trouble with Fuel Additives

Several decades ago, when Congress granted the Environmental Protection Agency increased powers to regulate America’s air and water pollution, outboard motor manufacturers were forced to take notice. Inefficient 2-stroke engines had been the norm up to that point, and it was agreed that the outboard companies would either have to drop 2-strokes from their product lines entirely or find a way to make them more eco-friendly.

As evidenced by the newer offerings from Mercury, Evinrude and Yamaha, motor companies found innovative ways to boost efficiency. While most of these attempts were successful, others were ill-advised. This was especially true of the additives that were suddenly being used to supplement marine and auto fuels. An additive called MTBE was thought to bolster octane rating and to burn more of the hydrocarbons and carbon monoxide in the exhaust.

Unfortunately, MTBE also turned out to be a serious contaminant that mixes easily with water and seeps into groundwater leaving pollution in its wake. The latest replacement additive for MTBE, ethanol, isn’t much better when considered in high concentrations. Its environmental impact is beneficial, but the substance mixes with water to create a sludge that can crack and clog outboard fuel systems. It just goes to show that motor companies and researchers have yet to find the perfect fuel additive blend. For now it’s best to stick with low-ethanol fuel and bulk outboard motor oil.