gas in oil crankcase. How else could gas get into oil.

[pstephens46]

Plasma is not what it used to be. I gave blood recently so they could mine some. Maybe plasma coming from bad blood is the problem. Not as sticky as it once was. I don't know.

Seems to just be a Yamaha branded plasma issue. According to TOS.

[28Regulator]

Knowing what we know about the propensity of an outboard motor to make oil, what would be the most useful recommendations that might be made? For the small percentage of the boating public that seems to have this type of an issue.

Let's hear some ideas from all.

I broke mine in by the book. Used dino oil in my 2014 F300s from 0-700 hours, and synthetic from 700-1050. No oil made from 0-800 hours, but both have been making oil from 800-1050 hours. I'm over 5% fuel dilution regularly now. I also stopped using ring free from about 600-900 hours. I ***** alot. I've switched back to dino to see what happens - should know in a few months if wind ever stops blowing.

My list would be, in no particular order:

1. Break in by the book - up and down with some high rpms to help get seated.
2. Use ring free.
3. Change thermostats as recommended.
4. Ethanol free fuel if possible.
5. Dino oil, instead of synthetic.
6. Run WOT occasionally when possible.
7. Sure I'm forgetting some . . . .

[pstephens46]

My gut says follow Mercury’s general 4 stroke advice for the F300. Run them a little harder than most. When is the last time someone killed a 4 stroke with the break-in paradigm?

[pstephens46]

I bought the Mercury "F90" brand new - and obviously did NOT follow Mercury's instructions to the letter -
that engine has never been run over 5000 rpms.
(nor "made oil")

Surprised Boscoe didn’t jump on this. He did once before.....bout two years ago matter a fact.

How do you know that F90 is propped correctly? How do you know you are getting the best that motor can produce?

[boscoe99]

Natural way of thinking is that a motor is being abused when run at very high power settings.

Meanwhile 99 percent of piston aircraft motors take off every time at 100 percent power. Day in, day out. To no harm.

Most will then perform at 75 percent of max power for the duration of the flight after take off.

Running very hot the entire time.

[boscoe99]

I bought the Mercury "F90" brand new - and obviously did NOT follow Mercury's instructions to the letter -
that engine has never been run over 5000 rpms.
(nor "made oil")

Surprised Boscoe didn’t jump on this. He did once before.....bout two years ago matter a fact.

How do you know that F90 is propped correctly? How do you know you are getting the best that motor can produce?

Good point.

[walleye1]

These engines run uphill all the time, running at 1/4 to 1/2 throttle is harder on them than running wot.

[99yam40]

These engines run uphill all the time, running at 1/4 to 1/2 throttle is harder on them than running wot.

that is something I have not really thought about before.
But if the HP rating is at 5500 or 6000, and you run them at 3K or 4K RPM how much HP is there for turning the prop.
being that same prop has to load the motor at all RPM

[fairdeal]

These engines run uphill all the time, running at 1/4 to 1/2 throttle is harder on them than running wot.

On a planing hull, yes.- but once on plane water and air resistance increase as the square of velocity.

I “feel” - no evidence - that the engine is working “easiest” where torque peaks on rpm curve -
which is probably well below max HP / WOT

[walleye1]

On a planing hull, yes.- but once on plane water and air resistance increase as the square of velocity.

I “feel” - no evidence - that the engine is working “easiest” where torque peaks on rpm curve -
which is probably well below max HP / WOT

Just what i was taught and told by some great tech's.

[pstephens46]

We have done so much with so little for so long that we can now do everything with nothing at all.

I am guessing that it is a four stroke of some kind. Might be a Yamaha brand. I have been known to guess wrong. A Pratt & Whitney PT6 perhaps?

PT6 is not specific enough.....You can do better.

[boscoe99]

PT6 is not specific enough.....You can do better.

Sorry. PT6A-67P

[BQUICK]

A Mercury dealer I worked for would run the new motors for 10min at double oil idle then wide open for 2 minutes to "seat the rings". Seemed to be a lot of happy customers....
(sorry talking 2 stroke but still "ring sealing" going on)

[pstephens46]

On a planing hull, yes.- but once on plane water and air resistance increase as the square of velocity.

I “feel” - no evidence - that the engine is working “easiest” where torque peaks on rpm curve -
which is probably well below max HP / WOT

But what about having the most efficient propeller for all rpms?

[boscoe99]

But what about having the most efficient propeller for all rpms?

Is that possible?