TOPIC: 59 mark 78a oil mix

I believe the original stated oil mix for my 78a is 20:1. I've heard people say that with the newer oils you can run 50:1. What about synthetic oils. My motor was running good but there's a ton of oil in my test tank. I've heard dive synthetic oils are biodegradable. Is this true? I'd feel much better about the slick if that were the case.

Is it oil or LU grease? Of course at 20:1, it's not surprising that it's dumping it.

I ran my 78A at 40:1 without any issues. I heard 50:1 also but ran it around 40:1 just to be safe although I had guys telling me I was just wasting oil. Do the same for all my old Mercs. Mercs use needle bearings, at least in the "fully jeweled" models, instead of babbit, so they don't need as much oil as some older motors need.

20:1 is extremely heavy. I would be surprised, that even in the days of 30wt, that they would be recommended any heavier than about 24:1, more likely around 32:1. With Quicksilver, or any other good TCW3 oil, 40:1 should be plenty rich.

I felt there was so much extra I should evaporate the water out of my test tank and pour it back in my gas tank.

25-1 was the original mix

Believe Dave. Run it at 24:1 and be sure it will last. Its not the quality of oil, its the QUANTITY that makes a difference. Manufacturing tolerances were not as precise or accurate in the 1950's, so rings and bearings needed more oil to keep bad things from happening, that's why many old motors are still running after 60 plus years. I run Pennzoil full synthetic in all of my vintage outboards. Yes, it is 100% biodegradable and smokes less. Your oily residue in the test tank is normal. You can add a few DROPS of dish soap to make cleanup easier.

Ok..... I am totally confused. I thought 50:1 was MORE oil in the mix over say 40:1. I've always run 50:1.

I have a 63 1000. What's my optimal Fuel/Oil mix?


PS - I use penzoil synthetic as well.

You're running one ounce of oil to every 50 ounces of fuel. I'm doing one for every 20. I might have ran 20:1 because it was 8 years since it was used last. And I think they used 20:1 in this video which may have confused me also.

I've been around outboards all my life and know a number of marine mechanics. They've all said, to the last man, that running 40:1 or even 50:1 in old Mercs is just fine as long as the oil is rated TCW3. Now if your motor is modded for racing, different story.

If you want to be nostalgic and run 30 weight motor oil, then go by what is recommended.

Mercury, and a few other brands, used needle bearings instead of babbit bearings, and that is the difference. Babbit bearings do need more oil. Todays 2 cycle oil is worlds different than what was available when those motors were new. If you want to run 20:1 or 25:1, go ahead, it surely won't hurt anything except foul plugs faster and create more pollution in the water, but it's not needed. I've used 40:1 in late 50's Mercury Mark motors for years, used 50:1 in the newer ones. I currently have three Marks, and never ever had any problems. Even tore a few down after years of doing this and they were just fine inside.

I think Merc went to recommending 40:1 in the mid/late sixties and nothing changed inside the motor, the 2 cycle oils just got better then. 50:1 has been around since the early/mid seventies, I think OMC was even earlier.

Concur with Gregg, here's what Mercury had to say in a TSB issued many years ago:

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.

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.

Just a little anecdotal, back in the 80's I was running the heck out of a MK58A, Merc 700E, '64 Merc 1000, and a MK25 on a Quickie, amongst many others. All were run on regular unleaded and I usually used Valvoline TCW-"whatever" the rating was back then. Penzoil in those days was Death to an engine! I guess they've improved a bit since then.

Never an oil-related problem with any of 'em. They all ran like the Dickens, too!

Cheers.......ed

Gregg is right.

NEVER go more oil than a 50:1 mix or you are asking for it. Run a top rated TCW oil at 50:1, no cheap crap, and you will be a happy man. Adding more oil will cause ring sticking and heavy carbon buildup in the engine, and you will learn all about engine rebuilds as a result, not to mention the wasted oil and extra pollution you will be causing. Don't run more oil than 50:1 unless you have a race engine or are breaking in a new powerhead. Period. I have seen many powerheads ruined by guys who think more is better when it comes to oil, and it sure brings a lot of extra revenue to my shop!

My 1986 Inline 115 has run 40:1 Quicksilver Premium Plus since new. I know, I'm the ONLY owner. Compression is still 125 +- 5 in all holes and leakdown is less than 5% on all holes. Propped to turn 6200 with a 22" Turbo II on a heavy 15' Glasstream 15V bass boat. So please DO NOT say never run richer than 50:1. If you've had busted engines in your shop, it's not from too much oil. Over propping, lack of regular maintenance including regular use of something like SeaFoam in every tank of gas, even lack of regular water pump maintenance. But NOT from 40:1 or even 32:1 oil. If you are regularly and for long periods running 6K plus revs, 32:1 is frequently recommended.

JMNSHO and, of course, YMMV but that's based on a lot of experience with older motors.

Respectfully I beg to differ. As a man who makes a living wrenching on these things I can tell you without hesitation that if you are running with more than the recommended oil mix you are asking for trouble. Without question. And sir, I will back that up with 38 years in the trade and thousands of hours correcting the mistakes of others. What you do with your own engine of course is your own business, but you do so at your peril.

Stick to good oil at the recommended mix, prop the boat right and do your maintenance by the book and you will have a long and happy relationship with your boat. Screw around with snake oil additives and improper oil mix and you will get to know you local repair shop intimately. Don't believe me? Well that's OK, we will be here when you need us.