2019 DF300 Making Oil

[Triton2300]

Checked the dipstick a few weeks back and noticed the level was an inch above the full mark i sent a sample to Blackstone Labs and it came back 5.3 percent fuel dilation.i posted on another site but wanted to also get some opinions on this site. I am going to have a Suzuki mechanic check the thermostats (change them), check the VST float adjustment (thanks Moonlighter), and check the fuel injectors for leaks.
I have a fly by wire set up and have noticed that my C10 display fluctuates 50 to 100 RPM at all speeds. Even idle. Would this be normal? I never noticed it before until this summer and am not sure if this is normal or a slight miss in the engine.
The procedure I do to check the oil is to have the marina pull the boat, put it in a cradle, level the enGine with a level and check the oil multiple times so it is done the same way all the time. Any thoughts would be appreciated.

[Murray]

How do you usually run the engine PRM wise? As far as checking the oil I trim it down and check the oil, I’m not overly concerned about it dead level so long as the oil is between the high/low marks.

[Triton2300]

Usually run between 4 and 5k. No trolling and shut the engine off when I drift fish

[artdf175]

Thermostats?
always good to check them per the maintence schedule but not part of the problem you describe
Doubt the fuel injectors would be doing this
most common problem would be a sticky float valve allowing fuel to flow from the fuel tank into the crankcase
Moonlighter is good listen to him !!
Art
ps--pulling the boat out with a cradle is not only expensive but gross overkill..

[Moonlighter]

This is one for Red.

Paging Redlowrey !!

[redlowrey]

Last time I got into a serious debate about this I nearly got kicked off the forum, so I will be more diplomatic this time. I have a theory on this one, in the early days I was adamant there was only two ways fuel could get into the engine holder and that was either from a ruptured diaphragm on the low pressure fuel pump or from the vst over filling and getting drawn into the engine holder..
But I have to eat a bit of humble pie because fuel does get into the engine holder from the rings but not being blown past the rings on combustion or bores being glazed.

These engines that don't run an 02 sensor run nearly as efficient as the engines that do, meaning they run close to an open loop air fuel ratio of 14.7 to one in cruise so if you pull a plug out you will see that the porcelain near the tip is a light tan to white color indicating that combustion in the cylinder is good. Fuel in liquid form would have no way of getting past the rings because it is getting burnt but there is liquid fuel getting into the engine holder.

My theory is, these port fuel injected engines spray fuel towards the inlet valve, when the piston moves down the cyl on the intake stroke fuel and air is drawn into the cyl and on the opposite side of the cyl to the spray fuel that is in liquid form hits the cyl wall and condenses, as the piston moves up the cyl on compression if the top ring and the second ring gaps have lined up fuel will be pushed down past the rings and on to the top of the oil ring and around to the gap on the expander and into the engine holder.

The bigger engines that run an electric low pressure pump and run an evap system if the vst was over flowing the excess fuel would end up in the combustion chamber making the engine run richer which you would pick up from looking at the plugs on an open loop engine or the check engine light would come on with an engine that run an o2 sensor.

I think keep an eye on the level and change the oil if it gets excessive, I think my self the rings will eventually spin and it will stop on its own, I own a DF140 with nearly 2000 hours on it sometimes my level creeps up I will just change the oil, the things people have changed on there engines is staggering and they have to pay someone to do it.

I started my apprenticeship in 1967 when there were only carburetors, then went to electronic fuel injection, and probably rebuilt two hundred engines and not once did I ever get an engine back with a problem of two much fuel in the sump, then along come inverted four stroke engines in boats and we have this problem.

[Moonlighter]

Thanks for replying

So Red - is it worth the OP checking the low pressure fuel pump diaphragm?

[redlowrey]

He has got an electric low pressure pump that is controlled by the ecu.

[Murray]

Reason I asked about RMPs is if I do allot of trolling then my oil level will creep up. This past summer all the grandkids were up and the boat was used primarily to pull tubes and water skiers. Oil level didn’t increase at all this summer when the engine was working and working hard. I was going to pull the fuel pump and check the VST at the start of the summer but never got around to it. Now I’m starting to wonder if there is anything wrong with the VST and/or the fuel pump. My assumption was, until this summer, that if fuel was being dumped into the crankcase at low RPMs then fuel would also be dumping in at high RPMs only faster. It appears my assumption was wrong? 2009 DF90A

[Triton2300]

Thank you Gentlemen for the responses. I will have them look at the diaphragm in the LP fuel pump.
I have a question. I read somewhere the gas will dilute in oil up to 2 percent before you can smell it. The report from Blackstone said 5.3 percent.When I took out the excess oil from the sump, the Marina I keep it has two Yamaha mechanics. Neither of them and I could not smell gas on the dipstick or in the oil I took from the sump. I wonder why?
Artdf175- The boat is drystacked inside so it’s part of the service. It’s the same price keeping it drystacked vs. renting a slip and having it removed for service and stored.

[redlowrey]

Thank you Gentlemen for the responses. I will have them look at the diaphragm in the LP fuel pump.
I have a question. I read somewhere the gas will dilute in oil up to 2 percent before you can smell it. The report from Blackstone said 5.3 percent.When I took out the excess oil from the sump, the Marina I keep it has two Yamaha mechanics. Neither of them and I could not smell gas on the dipstick or in the oil I took from the sump. I wonder why?
Artdf175- The boat is drystacked inside so it’s part of the service. It’s the same price keeping it drystacked vs. renting a slip and having it removed for service and stored.

Mate you have an electric fuel pump, it only effects the smaller engines that have a mechanical fuel pump that bolts to the motor.

[redlowrey]

Reason I asked about RMPs is if I do allot of trolling then my oil level will creep up. This past summer all the grandkids were up and the boat was used primarily to pull tubes and water skiers. Oil level didn’t increase at all this summer when the engine was working and working hard. I was going to pull the fuel pump and check the VST at the start of the summer but never got around to it. Now I’m starting to wonder if there is anything wrong with the VST and/or the fuel pump. My assumption was, until this summer, that if fuel was being dumped into the crankcase at low RPMs then fuel would also be dumping in at high RPMs only faster. It appears my assumption was wrong? 2009 DF90A

Murray if your float needle and seat assembly does not hold its level, there is more chance of the vst over flowing and letting fuel being sucked out of the vapor line and raising the oil level when you are trolling.
When you run the motor hard you lower the over full level in the vst because you are consuming a lot more fuel than what is leaking past the needle and seat at its set height.
The easiest way to find out if your vst won't hold is to run the engine on the muffs for twenty minutes at 1000rpm and pull the vapor line off the top of the vst, if fuel comes out you know it is not holding.

[Triton2300]

Mate you have an electric fuel pump, it only effects the smaller engines that have a mechanical fuel pump that bolts to the motor.

Got it. Thanks

[Moonlighter]

Thanks Red, appreciate you lending us all your expertise, good to understand these things even though Im not going to tackle pulling this stuff apart LOL!

It seems bigger Yamaha outboards suffer a lot of this “fuel in oil” issue, I wonder if its something to do with the u-beaut cylinder coating that Yamaha introduced some years ago, you know, the stuff that allows them NOT to do ANY running in of new motors. Can run ‘em like you stole ‘em straight out of the showroom, apparently…..

The Hull Truth boating forum is awash with “Yamahas making oil” threads. Dont seem to see the same issue arising nearly as often for Suzukis or most other brands though.

On that basis I would be wary of Yamaha mechanics advising about this issue pertaining to Suzuki’s. 2 different beasts almost entirely.

[Murray]

Murray if your float needle and seat assembly does not hold its level, there is more chance of the vst over flowing and letting fuel being sucked out of the vapor line and raising the oil level when you are trolling.
When you run the motor hard you lower the over full level in the vst because you are consuming a lot more fuel than what is leaking past the needle and seat at its set height.
The easiest way to find out if your vst won't hold is to run the engine on the muffs for twenty minutes at 1000rpm and pull the vapor line off the top of the vst, if fuel comes out you know it is not holding.

Thanks, I’ll add that to the list to check next spring.