Originally Posted by Lmarth

Just a few observations. Harrisonmirage makes a good point about the potential for distributor gear wear with the heavier oils. In a prior life I ran straight 50W in my BBC race car and chewed up not only the distributor gear but the cam gear on a couple very nice General Kinetics cams. When that happens you get "spark scatter" because the rpm of the distributor shaft is erratic and isn't always firing at exactly the right time. The senders/guages aren't always accurate. Mercruiser provides the boat builders with a manuals package (or did in 98 when my boat was built) for their engines/drives. As I recall,the package for my 800SC's cautions that the guages may be off slightly. The multi-viscosity synthetics today hold up much better than when they first came out (my opinion) and I've got nothing but praise for the 15w-50 Mobil 1 Sterling recommended when they refreshed them in 2000. Some people get scared when they see relatively low oil pressure at idle with BBC's. I'm looking now at the Mercruiser Service Manual. It says you should see a minimum of 30PSI @ 2000 RPM. All you have to do is move off idle to see your oil pressure go up to more than the minimum spec. Maximum is 70PSI @ 2000 . All the big blocks in the manual call for 30-70 @ 2000 RPM. For what it's worth.--Lou