Originally Posted By: ledslinger
On Mercury Marine website it has this comparison between what is likely 15W50 Mobil 1:
Here are the results from a comparison test between Verado Oil and a popular 15W 50 full synthetic oil.
Verado oil shows significantly better shear stability and volatility, and is higher in viscosity and High Temperature High Shear (HTHS) after shear.
The popular competitive formulation uses a fair amount of VM (viscosity modifier) which is subject to shear, while the Mercury oil contains no VM. As a result, the Mercury oil will hold its viscosity far better in difficult situations.
The HTHS after shear follows along with the viscosity stability, which results in improved bearing protection.
Use of the full synthetic competitive oil resulted in higher oil consumption than the Mercury 25W-50.
This indicates apparent concern over shearing and viscosity breakdown.
One factor that likely drives oil recommendations by marine engine manufacturers is potential duty cycle. They have to allow the possibility the motor will be hung on a barge and run at 3/4 throttle for 15 hours straight. My buddies boat will rarely see a minute of continuous use above 3/4 throttle.
Still pondering to stick with the Merc 25W50 after warranty expires on my buddies boat. Just got back last week from trailering it over 3000 miles round trip to the Florida Keys. He took it fishing to the Bahamas and burned over 700 gallons of fuel. Talking to him during the drive I found he has never ran it full speed or even a full throttle acceleration. I said maybe this indicates you only needed 2 engines. He just chuckled like 2 motors was an absurd proposition.
