Reply To: Johnson PO-15 Oil recommendations

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April 13, 2023 at 9:04 pm #275131
Mumbles
Participant

    A lot of older motors never used seals of any kind on the crankshaft and relied on the heavier oil in the mix to help seal the motor. Todays TCW III oil is about a 5 W and is designed more for flowing thru injectors on a cold day than sealing a motor.  Some guys have used detergent free piston engine aviation oil in various weights with good success.  Note that W100 aviation oil is SAE 50W and W80 is SAE 40W etc.