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Yamaha Motorcycles
Fuel and Engines
Oil and Oil Filters

If 4 stroke oil is put into a 2 stroke engine will it damage the engine?

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December 18, 2014 2:54PM

The biggest difference is this: 2 stroke oil is designed to be burned in the combustion chamber, 4 stroke is not to be burned and is to be in a crankcase, so 2 stroke oil is designed to not leave deposits on anything in the combustion chamber when burned. (deposits on spark plugs, valves (or reeds) etc. 4 stoke when burned will leave a blackish deposit that is hard to remove on all these parts, so much so that it is recommended that you change the plugs if you fog an engine with 4 cycle oil by mistake. In very severe cases with prolonged use, it can leave so many deposits that it will cause the engine to keep quasi running when it is shut off/ they have to be removed by injecting water into the cylinders when the engine is running.

This can be done with a garden hose regulated and 2 people when the engine is running (one to control the throttle and make sure the water doesn't stall the engine), and will immaculately clean the combustion area. (any rebuild mechanic will tell you that it is so easy to tell if there has been a crack or head gasket leak as that cylinder will be immaculate where the water has been present) Doubt if you need to do that/ as again, that damage is only from very prolonged use.

Running the engine with a 4 stroke oil mix should not cause any damage in the short term, however, long term use will cause excess carbon build up that can lead to detonation and costly engine repair. The use of a quality 2 stroke oil is recommended.


no 2 stroke oil is designed to mix with the oil and fuel so it is pumped into the jug at the same time engine oil will not mix and plug the inlet.