Oil Viscosity in a 2003 Merc 4 stroke 75

[muskiechaser]

Merc lists two oil options based on temperature, 10W-30 and 25W-40 for use above 40 deg. Is there any advantage to using 25-40 oil? I had thought about using 25W-40 until my boat ride across Big Sandy on Sunday morning in 30 degree temps. That was fun

I am planning on using Amsoil if it makes any difference.

Thanks, John

[theoilman]

A 75 HP - yours must be an outboard. It has been my experience that most Mercury 4-stroke outboards prefer the 10W-30, while the I/O and inboards Merc. preferred viscosity listing is 25W-40.

The AMSOIL preferred products - for 10W-30 use AMSOIL prod. code WCT and for 25W-40 use AMSOIL 10W-40 prod. code WCF. These are both FC-W marine warranty certified for all marine applications.

For more info please e-mail me direct, and I will return you the data sheet and other info.