Oil in medium size 4 cycle outboards?

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Originally Posted By: Doc_Stressor
HTHS viscosity must be 3.3 at a minimum. Most automotive 30 weight oils are closer to 3.0. See page 21.


Yes, but that's different than what you stated earlier ("to meet FC-W specs, the oil must be blended to a higher viscosity"). Know what meets the FC-W specification? Pennzoil Ultra 10w-30, with a HT/HS of 3.3cP that comes in at 10.5cSt @ 100°C.
 
There are several automotive oils that would meet the FC-W standard for film strength. But most 30 weights do not. This would only be a factor in engines where fuel dilution is a problem. Some engines make oil, others do not.

But even a good oil like PU likely doesn't have the mixed boundary lubrication protection recommended for sliding tappets. Most high performance cam manufacturers recommend at least 1100 ppm zinc/phosphorous as ZDDP. Any diesel rated oil would meet this spec.

At least with FC-W rated oils, you know that what you're using meets the manufactures specs.

Lot of folks run automotive oil in 4 stroke outboards without problems. In most cases, difference in mean time before failure would only become apparent after thousands of hours. Outboards rarely fail from oil related wear issues. Most eventually fail from internal corrosion problems or fuel related issues that cause cylinders to run lean. Interestingly, these type of failures are often the result of infrequent usage rather than running time.
 
Originally Posted By: Doc_Stressor

But even a good oil like PU likely doesn't have the mixed boundary lubrication protection recommended for sliding tappets. Most high performance cam manufacturers recommend at least 1100 ppm zinc/phosphorous as ZDDP. Any diesel rated oil would meet this spec


There are plenty of cars still using sliding tappets. Ford Focus, many Honda and Toyota models....etc.

None of these requires a special oil.

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In a perfect world with a good wallet, i would use AMS or RP marine oil. If I had an older motor, I would play around with different oils... I would also be bored some and change the oil alot... I've used auto gear lube for years in my lower units, no problems.
My Friend hss a 250 SHO on his bassboat and he uses auto oil, no problems...
 
As I said I have been using NAPA 15-40 diesel oil in a Yamaha 115, with no issues at all. Had my oil get a little dilution, noticed the dipstick over the high mark, after a 45 min run at 5 grand everything was fine. That is the only time it has ever done that. I am considering going to Mobil 1 5-40 diesel not sure which one, there are two. I was worried about the 5 part but Yamaha's new syn is a 5-30. They say it can be used in all their engines. No thanks at $10-12 a qt.
 
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