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Yamaha F300 making oil?

Old 06-11-2021, 03:28 AM
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Default Yamaha F300 making oil?

My Yamaha f300 is making oil. The motor has 1250 hours on it. I understand about originally seating the rings but this is not a new F300. What could be some other causes I could look at?
Old 06-11-2021, 03:29 AM
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injectors
Old 06-11-2021, 03:34 AM
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Always made oil, or just started making oil?

Assuming just started making oil, then perhaps worn rings? Compression test.....or maybe injectors....

If always made oil, then maybe rings never seated.

Check thermostats/temps....maybe running cool....
Old 06-11-2021, 04:19 AM
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I'd do a leakdown test and send a camera in each hole to look for carbon. If that checks out next make sure all holes are firing and if they are send out the injectors.
Old 06-11-2021, 04:38 AM
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Search Amazon for new injectors. These are Mitsubishi engines.
Old 06-11-2021, 05:30 AM
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Shock it with Yamaha ring free.
Old 06-11-2021, 05:31 AM
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Carbon build up on the piston rings, or change of usage pattern, may do it on an older higher time motor.
Old 06-11-2021, 05:32 AM
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Two stroke injectors are thought to clog up over time and cause a motor to run lean. Is the thinking that four stroke injectors don't flow less gasoline but more gasoline over time?
Old 06-11-2021, 05:33 AM
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Originally Posted by alloyboy View Post
Carbon build up on the piston rings, or change of usage pattern, may do it on an older higher time motor.
I hear Rotella diesel oil is good at cleaning carbon out of a motor.
Old 06-11-2021, 05:38 AM
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Originally Posted by critt77matt View Post
I hear Rotella diesel oil is good at cleaning carbon out of a motor.
Is this sarcasm?
Old 06-11-2021, 06:21 AM
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So it just started making oil or is this an older issue?
Old 06-11-2021, 06:33 AM
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When is the last time you changed your thermostats? If the engine is running cold, it might not be burning all the fuel in the cylinder head.

If you change annually, then you can cross this off your list.
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Old 06-11-2021, 06:44 AM
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Gasoline in the oil? Try an oil spectroanalysis lab to confirm it is unburnt gasoline before chasing down rabbit holes, IMO.
Old 06-11-2021, 07:45 AM
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1st and foremost I would make sure my VST is not overfilling above the float..and the fuel pressure regulator is working correctly...
Old 06-11-2021, 11:55 AM
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There’s another post about Tstats being a culprit
Old 06-11-2021, 12:23 PM
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To be more specific, I noticed the the port side motor running less oil pressure. So I googled it, possibility of fuel in oil, thinning the oil equals less oil pressure. So I checkt the oil, yes the oil was high on the stick. I changed the oil this week and my oil pressure went back up. At the end of my 150 mile run yesterday I noticed it was back down.

I haven’t been able to get back out there and check it, but I’m guessing there’s fuel in it. I have had this set for just at 100 hours as I purchased them from the owner of a Yamaha shop that personally know and he gave them a seal of approval. The motor also runs strong just like the other one.

I will have to check the thermostat and VST.
I need to get a leak down test kit and do that as well.
Old 06-11-2021, 01:45 PM
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Originally Posted by 6104696 View Post
Is this sarcasm?
I know the tht Gods will disagree but I run Rotella T6 in everything I own. No problem
Old 06-11-2021, 02:26 PM
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run it like you stole it
Old 06-11-2021, 03:05 PM
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What’s your rpm at wot? My f300 made oil when it was over propped, but it went away with a prop change and running it hard. Bought used.

as I recall it also tended to have low oil pressure at idle and when I checked that was normal for those motors.
Old 06-11-2021, 03:16 PM
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I have twin F300s on a 25 open same as the 28t. I rarely get over 4500, because the cost and it’s hard to find a day to ride 60mph.

I have 22p bravo 1s, I can get 5900 so I’m not propped to high.

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