Tips & Tricks: Small Engine Gas Issues

Whether it’s a snowblower, lawnmower, generator, weed-eater or any other small engine, its inevitable that you’ll eventually have some issues – often at the beginning of the season when it sat without use for many months.

During the first three years of university I worked part-time & summers in a mechanical shop. Since then I still work on small engines regularly as somewhat of a hobby. By far, the most common issue I saw both then and now when a small engine came into the shop could be traced back to issues with the gas.

While there are many origins of small engine issues, undoubtably one of the most common (locally at least) is due to ethanol in the fuel. Ethanol has four major problems when it comes to small engines:

  1. Ethanol attracts and absorbs water from the air (hydrophilic) leading to water in your gas leading to increased corrosion and loss of power. Additionally, with increased time and elevated water concentrations a phase-separation will occur.
  2. Ethanol gels when mixed with some non-ethanol-compatable fuel stabilizers. This creates a thin red gel in the fuel tank. We’d see this on an almost daily basis in the shop andmechanic-1673079_960_720 while it can be fixed by fully cleaning the tank and carb, it’s time
    consuming and expensive.
  3. Ethanol is corrosive to many of the seals used in small engine carburetors, especially
    at concentrations higher than 10% (E10+, E15)
  4. Ethanol is a very effective cleaner. While this can be used to your benefit in controlled situations, rapidly cleaning out the fuel system after years of buildup can result in debris accumulation in fuel lines and carburetors, and blocked fuel filters.

Tips & Tricks to Eliminate Small Engine Gas Issues:

  • Use zero-ethanol (E0) fuels. The ethanol percentage is (almost) always printed on the pump for each available grade. Often the premium grade(s) contain no ethanol while lower grades often contain 5-15%.
  • Buy only enough fuel to last 30 days. Water absorption and ‘souring’ happen over time – only buy as much as you expect to use within a month to ensure you’re always using fresh gas. A surprising amount of transpiration occurs in seemingly solid plastic gas cans and rubber hosing which both lets valuable gas vapours  escape to the atmosphere and lets moist, water filled air into the gas.
  • Avoid any gasoline mixed with methanol unless the engine has been specifically designed for its use as outlined in the users manual.
  • MTBE (methyl tertiary butyl ether) should be limited to 15%. MTBE creates a cleaner and more complete combustion and as such reduces environmental and air quality concerns associated with combustion engines. Concentrations above this level are very rare and are only usually the result of over-dosing octane boosters added by consumers.
  • Use a fuel stabilizing additive to reduce water absorption and varnish build-up. We use two, ‘Sea Foam’ and ‘STA-BIL 360’ almost interchangeably but they do each have their strengths and weaknesses. In both cases they’re ethanol compatible. Whichever stabilizer you choose always ensure it’s ethanol compatible and designed for gasoline.
  • Drain all the gas and complete the rest of a seasonal shutdown when the engine won’t be used for an extended period of time. This’ll only take 15 minutes but will prolong the life of your equipment by many years and make the next start-up significantly easier.
  • If you’re having a hard time starting an engine the first thing you should check is the gas. Simply by smelling the gas you can often quickly tell if it is old and ‘soured’. Sour gas has a distinctive slightly sweet varnish smell. Additionally, you can remove some gas from the tank and inspect for obvious aging signs of spoilage such as dark (red/brown) colour, cloudiness or an obvious phase separation.
  • There is no effective way to repair spoiled gas. It must be disposed of correctly and replaced with new gas.
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