2-cycle oil pooling after using Sea Foam Motor Treatment in outboard [SOLVED]

When wintering my 1990 Yamaha 130HP two-stroke outboard, I added Sea Foam to the non-ethanol gasoline in my boat fuel tank and ran the engine on my driveway using a garden hose for cooling. The engine gave off a large amount of smoke, which I understand this to be normal. (?) After 10 minutes I pulled the fuel line allowing the engine to run out of gas. I replaced the plugs as some were quite fouled with carbon. My problem is, I noticed oil pooled beneath the outboard. This is an oil injected engine so am I to assume this is caused by two-cycle oil getting into the exhaust? Additionally, I’m an engineer with a background in engines.

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Jim D.
Jim D.
3 years ago

Thanks for the questions and description Bill. Here are some answers based on two-stoke oil and plug fouling. Two-stroke engines/oil and exhaust: After your outboard’s oil is injected into the crankcase, some of the oil is drawn up a transfer port with the fuel/air mix and is combined with the fuel in the chamber, then pushed out the prop exhaust with the cooling water. When running a two-stroke outboard on a trailer, the oil pooling is noticeable because much of the oil molecules can remain unburned and drain out with the exhaust water. By dding Sea Foam it worked to liquefy heavier oil residue that built up in the engine, causing the old oil to get flushed through the exhaust. Carbon on plugs: Carbon buildup on plugs is normal, while excessive buildup might cause you to consider doing more to keep the upper engine areas/plugs clean.

What I’d do: Run Sea Foam Marine PRO in every tank plus an occasional higher concentration will work to minimize all types of oil and carbon buildup. Better performance and cleaner running will be noticeable! Hope this helps!