90 HP 4 stroke Mercury outboard

[mpcross]

Hi All, it has been 20 years but I bought a new boat and motor. My old motor was a 2 cycle and I now have a four stroke EFI. The only info I can get on oil is from the owners manual and I hope you can help me with some input or some Ideas on some oil to use on this motor type. The owners manual says to only use Mercury or Quicksilver NMMA FC-W cetified oil 25W-40. Also, Mercury and Quicksilver only comes in syn. blend.

I would like to understand the difference or the comparitive difference between the NMMA FC-W oil to a automotive CJ-4 etc, type motor oil,if there is such an thing.

I want to switch to 100% class IV or better fully synthetic oil, in as low as is safe viscosity, on the low end.

As we know, in the automobile world it is normally 5w... somthing oil as apposed to 25w... something oil.
I am trying to find out why,with a brand new and I assume new tecnology motor why so heavy a weight oil?
Is there some special parts,cam coating,lifter issue,belt or other part that may require the 25w on the bottom?

Is there any brand(s) automotive labeled oils that have been tested in 4-stroke outboards, fully synthetic, that can compare to the NMMA-FC-W cetified oils?

I have less than 3 hours on the motor but want to change the oil filter and top off with a fully synthetic until I change the oil a 8 hours of break-in.

Thanks in advance for the info, MpC

[TheMotorOilSite.com]

I would suggest sticking to an NMMA FC-W oil to make sure that you're using a lube that is designed for marine use. It really is a different animal and needs an oil specifically designed for that environment.

That being said, the only reason that the Mercury/Quicksilver oil is labeled 25w40 is because nobody else makes such a viscosity, so customers will feel obligated to purchase the OEM oil so as to match the owner's manual rec. This is not necessary.

A fully synthetic 10w40 or 15w40 motor oil that meets NMMA FC-W classification will be a perfectly appropriate choice for such an application. I wouldn't go to 5w or 0w oils, as these engines get pretty hot, and are not typically run in cold weather when a 5w or 0w oil would really be of any benefit anyway. Not sure you could actually find an NMMA FC-W oil in a 0w or 5w viscosity anyway.

That's my .02. AMSOIL's 10w40 marine oil would work very well for you. Others may as well. Just do your homework and check the specs carefully.

[mpcross]

Thanks for the rapid reply. I am glad to hear Amsoil has a 10w (Full syn.) product that will work. I will check with the RP and redline folks too. I figured the certification issue would be the kicker and that it was a different animal. I just did not know. If there are any sites that explain the NMMA-FC oils and their differances,that you know of, I would be glad to read them. MPC

[TheMotorOilSite.com]

You may find the following useful in at least understanding the process of NMMA FC-W certification and the test requirements of that certification. Look toward the end of the document for the actual testing value min/max values.

http://tinyurl.com/anplar

[mpcross]

Thanks Much,MPC

[TheMotorOilSite.com]

You're quite welcome.

[mpcross]

Just an update guys on the 4 Stroke oil. I have almost my required ten hours breakin on the motor and want to aquire a Amsoil Bypass (Marine) system for the motor. My old Bypass system is not only the automotive version but it has the cast aluminium mounting plate. I am curious if anyone knows if the new billet mounting plate that fits to the oil filter flange on the motor will fit in the tight spot? I do not know what the demensions(Dia.) of the mounting plate is,does anyone out there know? Thanks MPC