What Kind of Oil Should I Use in My Lawnmower?

Due to changes in automotive motor oil formulations, it is no longer recommended to use automotive oils in air cooled engines.

What changed about automotive motor oils?
The allowable levels of Zinc and Phosphorus were reduced by about half in 2010 and that’s after they had already been reduced in years prior to 2010. This reduction lowers the thermal conductivity and anti-wear properties of the oil. Air cooled engines are impacted by this change much more than water cooled engines because air cooled engines depend on the motor oil to carry heat to cool the engine.

Why was this change made to automotive oils? When automobiles consume oil, these elements exiting through the exhaust deteriorate the car’s catalytic converter, accelerating catalytic converter failure causing increased emissions.

What about synthetic oils like Mobil One or Castrol Syntec? If an oil is intended and marketed for road vehicle use then it falls under this regulation and even though it is synthetic it lacks the needed zinc and phosphorus levels to provide maximum protection for air cooled engines.

Are there synthetic oils formulated for small engines available? Yes, among the offerings, Kawasaki offers a synthetic blend motor oil and Toro offers a fully synthetic air cooled motor oil. We carry these products and also offer conventional non-synthetic oils formulated for air cooled engines.

Are there additives that can be used with standard automotive oil to increase its protection for air cooled engines?Yes. One such product is GM’s EOS (Engine Oil Supplement) part # 88862586. Our experience has been that it’s less trouble and less expensive to just buy oil that has the right formula to begin with.

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