right oil for new 90 4s merc

[woodchip]

Doing end of season service on a new 90 4s.

The service manual reccommends 25w40 except in low tempertures below 40 F and then they say to use 10w30.

I don't go out below 50 F.I would rather use the manufacturers preference.

My problem?Argued with a master mechanic over the grade of oil to use.He was very belligerent while arguing that in our climate you had to use 10w30.

I often end up working on things I am not familar with and for me,when in doubt,do what the book says.

I don't know much about the current technology for these engines but assume the manufacturer has speced the most appropriate oil for its design.

Am I wrong?
opinions?

 

[LubeDude]

Re: right oil for new 90 4s merc

I see no reason to use the 10W-30. You are somewhat limited as to what oils you can buy in the 25W-40 though.

 

[TheOilDoc]

Re: right oil for new 90 4s merc

Higher viscosity oils will give you better protection at higher temperatures (shear stress, etc). For the best protection, you should always use the highest viscosity oil recommended for your conditions.

Your engine manufacturer dictates a 25W-40 viscosity for the temperatures that you use your outboard. So 25W-40 is what you should use. Using a lower viscosity oil may not be as beneficial.

Your engine maker knows much more about what the engine requires than your mechanic. Not to mention it is your outboard. If you decide to operate it in colder temperatures, then simply drop to a lower viscosity.

Your Merc dealer, or most reputable marine parts stores, will carry a 25W-40 FC-W oil.