# Marine oil vs Mobile One Synthetic?



## SiXeVeN (Jul 7, 2007)

I am in the process of doing an upper and lower lube change on a 15hp kicker outboard. I have always used marine (usually brand specific Mercury oil in Mercury engine) grade oil.


Question is... Marine oil is always conventional or maybe synthetic blend. The lube quality of a full synthetic is far greater than conventional oil, not to mention the life span. Would it not be better to run a synthetic like Mobil One vs the Mercury/Honda/Yamaha conventional brand?

Curious what you guys think??


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## BarryL (Aug 21, 2003)

Hello,

I don't know that much about your OB, or OB's in general. I do know a fair amount about automotive gasoline powered engines and marine auxiliary diesel engines. 

I use synthetic oil in 2 of my 4 cars. One is a small displacement turbocharged engine in a race car. The other is a high reving high output engine. The other cars are not special and I use regular oil in them

I don't believe that a marine engine for sailboat would benefit from synthetic oil. Compared to a car, the oil in a sailboat engine leads a pretty easy life. No real cold starts (below freezing), not much idling. No hard starts and stops. Low RPM. The typical marine use is to start the engine (and usually the coldest temperature a marine engine will see is the 50's), let it warm for a bit, set the throttle to cruise speed, and leave it there. After some time, shut the engine down. From a lubrication perspective, that's about as easy as it gets.

About the only difficult thing I can think of regarding marine use would be relatively long engine off periods. This can allow the oil to drain off the cylinders and make cold starts more difficult. A synthetic would help here, but this is a real minor point. 

A few more points: Synthetic oils last much longer than standard oil. However, in a diesel engine you typically change the oil because the oil is contaminated with soot and other dirt. Synthetic oil will still have to be changed often as it gets dirty. And (IMHO) you should never go more than a year between oil changes. 

On my boat, with the small diesel (Universal M 25) that runs for maybe 50 hours a year, regular oil, changed in the fall before haul out, is good enough.

Barry


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## TSOJOURNER (Dec 16, 1999)

SiXeVeN said:


> Question is... Marine oil is always conventional or maybe synthetic blend. The lube quality of a full synthetic is far greater than conventional oil, not to mention the life span. Would it not be better to run a synthetic like Mobil One vs the Mercury/Honda/Yamaha conventional brand? Curious what you guys think??


Lots of things to explain here. Apparently I'm not good at doing that. So here's the short of it -

There's a lot more to oil than just "lube factor". Most "manufacturer labeled" oils are just re-brands of some other oil with perhaps some extra additives specific to their engines. What's important is what's not on the label. Those of who use nothing but Valvoline conventional in cars, Valvoline 20/50 Dura-Blend in motorcycles, and Castrol in 4-cylinder engines, know that unless you start off a brand new engine on M1 Synthetic you are wasting your money in both performance and loss of oil in blow-by. A "used" (non-synthetic history) engine has a few thousands inch more space between all the moving parts. M1 is so slick it will run right by your rings and go out the exhaust. With it goes compression, and fouled spark plugs, etc. And, not to mention all the other little leaks that will show up in a "used" engine. There are also many corrosion inhibitors in marine oil that you will not get in any other oil. Just like the 20/50 oil we use in our bikes. Even though it doesn't say so on the label, it has additives in it specific to air-cooled engines. Don't be fooled by long life claims by the manufacturer either. M1 gets dirty just as fast as any other oil. Usually way faster than regular oil in a "used" engine. However you want to rationalize it, with dirt comes premature engine wear. I think M1 is a waste of money no matter how you look at it. Stick with a good marine oil specific to your engine. Best of luck.


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## groundhog (Jun 27, 2006)

You might be able to get both marine and synthetic at the same time. Check out Amsoil on the web.


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## Maine Sail (Jan 6, 2003)

*I agree with*

I agree with Texas on Mobil 1. The only car I have that runs Mobil 1 is a high spun M3. BMW shipped it from the factory with BMW Synthetic (basically Castrol Syntec) and it uses about a quart every 1.5k. BMW of course says this is "normal" in the M engines running synthetic.

After doing some oil analysis it was advised that I go with a 4k change interval on this engine NOT the 8k -15K Mobil says you can do. With a little over 7 quarts this gets ridiculously over priced considering my wife's Honda Pilot with 130k uses no oil, has always run conventional and at 4k the oil is still quite clean & not brown. Her Pilot engine is cleaner inside too than the M3 is..

I do about 70k per year and rack up a lot of miles on vehicles and have yet to have any engine oil related failures, worn engines that burned oil etc. in the last 25 years, none, and nearly ALL my vehicles run conventional. The three cars I switched over to synthetic had numerous oil leaks all beginning within a few days of conversion. Two rear mains on turbo Volvo's.. $$$$$ I stopped doing that..

My brother is big wig at a company that manages fleets of vehicles world wide. They have PILES of data on every kind of fleet from 18 wheelers to sales rep vehicles to GPS tracking data and avg speeds, mpg etc. etc.. They can even tell you that the average 25 year old male driving a Ford Taurus will get 22.5 mpg and that a 25 yo female will avg. 24.5 mpg.. They have all the maintenance data at their disposal and they do sell it, as it is another revenue source for them.

About a year ago, when I was really fed up with the BMW's oil consumption and incessant leaks, I asked him to run some numbers and see if they saw any difference between fleets running synthetic vs. conventional. Some of the big trucking fleets now run it as well as some companies that want to be "greener".

The answer was surprising. The data showed more engine oil related repairs in fleets of vehicles running synthetic. Everything from leaks to total engine failures but mostly, and this was the big one, cars that just ran out of or got really low on oil. With the higher change intervals vehicle drivers had synthetic cars run out of oil and cause damage more often than conventional oils they also had more repairs to stuff like valve cover gaskets etc..

No one doubts synthetic is "more slippery" the question is does it need to be? If you were to ask my brother-in-law, if he thought synthetic was necessary, he'd point you to his early 90's Accord with over 600k on the original engine and tranny and ask why??

Just change it frequently and you'll be fine.


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## tommays (Sep 9, 2008)

USE the mercury high performance plus in the lower unit as it has a very good ability to function with a LOT of water should the gear case have a leak and NOT become a big freaking mess to DRAIN 


Its not recommended to use syn oil in 4strokes outboards due to fuel dilution and theirs plenty of oils that meet there spec


If Tohatsu 4-Cycle Oil is not available we recommend using an NMMA Certified FC-W 4-cycle oil formulated for use in outboard engines. Look for oils bearing the FC-W trademark.


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