Anyone other than Merc offer this in synthetic or synthetic blend? What's the difference between the FC-W spec over using over the counter bog box auto parts stores such as Mobil-1, Pennzoil, etc?

thanks

Merc didn't even have synthetic oil until about 5 years ago and before that they said synthetic was "too slick" for their roller cams.

I have used Mobil 1 15w-50 for the last 15+ years in my boats. Better oil and less expensive than Merc.

What is with the catalyst safe labeling on the merc oil, aren't all oils safe for the merc catalyst engines ?

Any oil for regular automotive use is catalyst safe. Some offroad or racing oils may not be "catalyst safe" but I can't even see how they could hurt a catalyst unless you are burning a lot of oil.

I just switched to Mobil1 15w-50 ,always used GTX 20w50 but was getting hard to find around here so I switched to Mobil 1,
How often do you change your oil?

My 1988 Merc is so old the book says I have to use titanium flavored oil straight weight 40 detergent.

My current 502mpi's--once a season +/- 50 hrs.
My old 525SC--25-30 hrs

Mobile 15-50 every 25 hours on my 496

the FC - W is the stamped of testing that the NMMA performs for marine oils. One sends in their oils to the NMMA testing facility and pays the fees per each oil weight. The NMMA does certain testing that has to meet and pass their testing standards to obtain the FC - W stamp / criteria .

Volvo penta up to 5 years ago motor oil was a straight 30 W syn. but changed all that under testing for their current recommendation is 10 w 40.

for marine apps and IMO even for CAT engines 1300 ppm of phos and 1300 ppm of zinc should be a motor oil used. These are 2 very common anti wear additives in motor oils.

The marine LS engine some are running / recommended 5w - 30

Driven racing oil for the engine and drive oil is what I use in my personal stuff.

For the poster who said Lucas makes Merc oil -- Lucas makes ZERO oils for Merc. Some of Merc oils are made by Citgo. and the prem gear oil sold by Merc is made by Citgo. I have all the spec sheets whom makes what for Merc .

Do not use current diesel oils for off road performance anything. The zinc and phos is really low for anti wear additives. They do contain alot of calcium for cleaning / soot.