I've been using Seafoam Marine in my gas for about 6 weeks now, and it's really made my 2004 Yamaha 150 performance improve. Quicker start-ups warm-ups, no stalling at idle, smoother and quieter at lower speeds. The advertising says it can be put in the oil as well. Will adding it to the oil improve performance even more, or will it be overkill?

I understand that I'm dealing with a 16 year old engine. Like a wise man told me once, if the performance improves after you pour in the additive, your engine was sick to begin with. But I'm trying to keep it going as long a possible without a rebuild, of course. When I got the boat in 2007, the compression was 125 per cylinder, now it's around 95. But it still gets me around.

Over at a Toyota4Runner forum, an opinion was that it's not good in the crankcase because it can 1) thin the oil and thereby lessen it's lubricity, and 2) it may free some old oil clogs and then stop up the delivery of the oil to the engine.

Thoughts?

I'm pretty sure "add Seafoam in your oil" is referring to 4 stroke engines Not 2 stroke. Thinning 2 stroke oil sounds like a really bad idea. Now if you 2004 150 is a 4 stroke then maybe it'll be ok.

Travis

If it’s a two stroke engine the gas and oil are mixed before it goes through the crankcase. So you’re already mixing it with the oil.
Four stroke? Sounds like a very bad idea.

These replies seem like the correct answer. Thanks for the info and I'm glad I asked.

Don't believe everything you read on the Internet. It can get expensive.

I wouldn't put anything in my oil ever, 2 or 4 stroke.

Sound advice right there... Dan

Seafoam is nothing but deodorized kerosene and alcohol. Cracks me up on how some people run nothing but ethanol free fuel then dump this in.

I have a 2016 Yamaha 150, 4 stroke. The only additive I use is RingFree. I will add a bottle of Marine Stabil when cold weather keeps me off the water this winter. Good thing about Alabama, it most stations have at least one or more ethanol free pumps.

seafoam in oil is for 4 stroke crankcase, 1 oz. per qt. of oil.

keeps carbon and sludge to a minimum and works good.

I was always under the impression that Seafoam was designed for 2-stroke motors (add it to the gas) Agree with the above, that I wouldn't add anything directly to the oil.

Amine/Nitrogen based detergents, like Techron and Redline Sl-1, were designed for 4-stroke motors (again, add it to the gas)

I dumped three bottles in the hemi a few weeks ago the mpg did go back up.

Sea Foam was first introduced as an additive for diesels. Worked so well people started using it in other motors. People use it because it works. I wouldn't add it to the oil.

I add a can to my truck crankcase a couple hundred miles before I change the oil. It cleans it out like nothing else. But I only have 512,000 miles on it so I don't really know if it's ok to use or not.