Re: 63 merc outboard 85hp
Mercury Bulletin Number 80-6:
"A. USE OF FORMULA 50-D OIL IN OLDER MERCURY OUTBOARDS
Formula 50-D oil can be recommended (at a 50:1 mixture) for use in earlier Mercury outboards regardless of year of manufacture.
Formula 50-D also can be used in other brand outboards (at a 50:1 mixture), provided that the manufacturer recommends use of a 50:1 oil mixture."
The above was copied verbatim from a Merc Service Bulletins Microfiche.
Since this bulletin was issued over 20 years ago, I'd expect that Mercury's latest oil formulations (and any good TCW3 oil for that matter) would be far superior to the Formula 50-D oil.
A caveat to the above would be that this recommendation was made for production motors. If you are boat-racing, or operating a "racing" motor, you of course should run a much richer oil mix.
25 years ago I ran the living Tar out of my old Merc 850-6, using Valvoline TCW or TCW-2 oil (all they had back then). Ran all my old Mercs at 50:1 with never a lubrication issue at all.
BTW if you do run your motor at 24:1 be sure to use a carbon-cleaning additive such as Seafoam, OMC Carbon-Guard, Yamaha Ring-Free, Chevron Techron, etc since carbon deposits will be more prevalent the richer the oil mix. And Merc piston rings HATE carbon buildup!
HTH & enjoy your classic Merc..................ed
