Why shouldn't I use Automotive Oil in my Lawnmower?

Automotive Oil vs Air Cooled Engine Oil

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. 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. Air cooled engines are made on a lower budget than automotive engines and don't typically have roller cams and other expensive systems to eliminate metal sliding against metal.

Why was this change made to automotive oils?

When automobile engines consume oil, these elements exiting through the exhaust deteriorate the car’s catalytic converter, accelerating catalytic converter failure causing increased emissions.‍

Will automotive oil damage my air cooled engine?

Using automotive engine oil is way better than no oil or low oil. No one is saying Automotive oil is poison.  But over time automotive oil will reduce the life of the engine with faster wear in high friction areas and higher operating temperatures.

‍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 products stocked at B T South are fully synthetic oils by Kawasaki and Toro which are formulated specifically 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 #'s 88862586 & 88862587. Our experience has been that it’s less trouble and less expensive to just buy oil that has the right formula to begin with.

*(A) Consult your engine owner's manual for appropriate fluid specs.

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* The viscosity chart above is provided by Kawasaki and is an appropriate guide for most air cooled engines. Remember viscosity is simply a measure of the oil's thickness or weight and nothing more. Maple syrup for example is approximately SAE 30 weight, but it would be a terrible choice to put in your engine. It is very important that oil meet the proper API spec, not just the correct weight.

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