Johnson PO-15 Oil recommendations

[david-bartlett]

Looking to see what other PO-15 owners are using for oil and oil ratios in their PO’s. I am looking for information specific to this series of engine.

Thank you!

[jerry-ahrens]

Hi David, I have a PO15 that I fixed up to use back in the late 1980s. At that time, I really was unsure about fuel/oil ratio, so I ran it 16/1 and used Johnson/Evinrude TCW3 oil. Through the years I switched to Quicksilver TCW3. The motor has always seemed to be happy and has stayed alive. The original specs called for double this amount of oil, according to my Johnson service manual. In my opinion, I would not go any leaner than 16/1, and a little more oil wouldn’t hurt it either. The PO 15 is a tough built work horse, but it needs the oil to keep the internal bushings alive. Using modern outboard oil on your motor will cause it to ”drool” some black goo here and there, because of the detergents added to the oil. Nothing to worry about. These old motors are made to run with more oil, and will smoke.. that’s the just the way they are. Hope this helps!

[Mumbles]

This table and the one at the back of The Old Outboard Book both show one pint per gallon, or 8:1.

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[david-bartlett]

Jerry and Jim,

Thanks for the replies. I am more interested in WHAT oil(s) people are running than the ratio. I plan to use plenty of oil, just wanted to know what others are using.

I know some rotary valve motors like a little thicker mix to help with sealing, and was concerned that the TCW3 alone might be too thin.

[rook49]

I use Sierra full synthetic TC-W3 oil. Works for me and I’ve found it’s cheaper than the other full synthetic oil that I’ve priced.

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aquasonic

[Chad Reeves]

Thank you all! Very helpful. Last weekend I acquired a PO-10, and after sitting for who knows how long after about 3-4 pulls it fired right up. I knew about the 16:1 fuel mix for the 1950’s engines, but this 8:1 is really good to know.

[aquasonic]

It’s interesting that you ask about what kind of oil. The Johnson T and H models from this time period recommended 40W oil at 16:1. Modern TCW-3 oil is certainly not the same viscosity as 40W oil. I’m thinking that TCW-3 oil is closer to 20W oil.

If the theory is that the heavier oil provides better compression, then does the thinner TCW-3 oil provide less horsepower and does it have a negative effect on achieving a low idle?

I can say from experience that a lower compression HD-25 model that I owned would only idle well with the heavier 40W automotive oil. Other motors with better compression seem to run just fine on TCW-3.

[Mumbles]

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.

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