New insight on 4 strokes "Making oil".

[JB]

I got this PM from Woodnaut on how he fixed a making oil problem. I have added it to the FAQ.

Thanks to Woodnaut for this info.
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I would like to submit a comment for your consideration. I was looking at the FAQ section, and particularly at the post on "Making Oil". This is an expert, well organized and lucid explanation of the causes of a four stroke making oil. I happen to have a 2006 Yamaha F90 and had this problem with it. As it turns out, it appears that a significant cause of my engine's problem was that I had it significantly over-propped which lowered by top end RPM to below 5,000. I went back to my old prop, WOT RPM went back up to nearly 6K and the problem instantly went away. The post alludes to this when it talks about combustion, but in my case over-propping caused such a dramatic effect that I wanted to mention it to you. Many Thanks and Best Regards - Woodnaut
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[gss036]

Re: New insight on 4 strokes "Making oil".

Over propping also causes the motor to lug down and will destroy the engine. Ever try running a stick shift car up a steep hill in 3rd or 4th gear?

 

[Chris1956]

Re: New insight on 4 strokes "Making oil".

JB, Why is it that the 4 cycle outboards do not get the oil hot enough to drive out the moisture? I have never had this issue with my sterndrive, and that lived and operated in a moist environment!

 

[JB]

Re: New insight on 4 strokes "Making oil".

Moisture is not the problem, Chris. It is gas getting by the rings into the sump that "makes oil".

Read the FAQ.

 

[TOHATSU GURU]

Re: New insight on 4 strokes "Making oil".

It's called fuel dilution and is common to all 4-strokes that cannot maintain operating temperature which very few do unless they are running over X RPM. Add in the effects of cold water and air temp and using too heavy of an oil or synthetic oil and it is a given.

 

[jevery]

Re: New insight on 4 strokes "Making oil".

I don?t think the contaminant is gas, but water, a byproduct of combustion. When I?ve drained oil in my Mercury 4-stroke, about a half quart of thin liquid, (water?), precedes the oil out the drain hole. It sure doesn?t smell like gas, and if the contaminant was gas, wouldn?t it follow the oil out the hole rather than precede it? My problem also cleared when I dropped 2? in prop pitch.

 

[TOHATSU GURU]

Re: New insight on 4 strokes "Making oil".

Water is possible under the right circumstances, however it is not a common problem.

From outboard manufacturer website:

"Because outboard motors have raw water cooling systems and run in varying water temperatures, unlike other water cooled 4-stroke engines, it can be difficult to maintain sufficient engine temperature in some geographic areas. Therefore, we do not always recommend using synthetic oil in our 4-stroke outboard motors, especially during break-in, due to the lowered engine temperature which could contribute to fuel/oil dilution."