6hp four strokes burn oil???

[Hank4268]

So we have 5 Yamaha four strokes (early 2000's I think) 6hp that all blow blue smoke at startup. They all run great and start on the first or second pull but smoke like crazy and leave a little slick on the water. After you run them they don't smoke at all. We run conventional 30W oil in them. Should we use a different oil or is it a ring problem? The hours on these are unknown but probably high. Any thoughts? Thanks

[boscoe99]

Are the motors kept on a boat or other type of water device? Water bugs come to mind. If so, are the motors tilted up when not being used or are the left tilted down?

If left down, oil can migrate across the piston rings and get into the combustion chamber. The motor may smoke like a chimney when first started. Once the oil has burned off no more smoke.

Sounds like what you may be experiencing. Completely normal. It would be unusual for all 5 motors to have worn rings at the same time.

If you were an old dog like me you would have been around when radial piston engines were used on airplanes. In a radial type motor some cylinders are upside down with the spark plugs on the bottom. Oil gets into those cylinders and causes the motor to smoke at start up. Take a look at this video. Note how the bottom cylinders smoke for a while upon start up. Same thing is probably happening with your motors.

https://www.youtube.com/watch?v=xaqjv0HbxyE

[Hank4268]

Yes the motors are left down on the boats in the lake. I'll try leaving them up and see if it makes a difference. Thanks

[rodbolt17]

motors left down tend to smoke at start up.

18cyl pratt & whitneys are awesome at start up .

[Hank4268]

Yes leaving them up does the trick. They smoke much less that way. Thanks

[boscoe99]

Thank you for the feed back.