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I have a 2011 Mercury 25hp 4 stroke. I'll be changing the oil for the first time soon. It came with non-synthetic oil in it. I was thinking about switching to synthetic. My two current vehicles (Toyota 4runner and a Mini Cooper) both specify synthetic. What are the pros and cons in a 4 stroke outboard?

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Hey blacksmithdog, I can't answer your question but am curious, since you have a new 25hp... I need to re-power my 13 Sport as well and am considering options; would love to get your thoughts. I'll shoot you a pm so as not to hijack this thread. Thanks!

Bruce

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I have been very pleased with Redline synthetic oils. They also have a synthetic extreme pressure grease that I use for my wheel bearings. The only cons I see is the increased price for synthetic oils.

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In that you have a newer year motor, before you just put synthetic oil in it, make sure it doesn't have to be programmed to use it. On my ETEC you can use either one, but it has to be programmed for the desired one

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thanks Tom, I need to go to Duncan's to get the filter, I'll ask them.

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Its a 4-stroke, it doesn't have to be programmed for synthetic. The ETEC is a 2-stroke and has to be programmed to run XD100 which is the only oil approved for that setting in an ETEC.

I know of no downside to running synthetic oil in your 4-stroke other than lightening your wallet a bit more.

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Synthetic oil is not really all that expensive if it is used according to the manufacturers recommendations.

Most cars today state in the manuals to change your oil at 5,000 or 7,500 mile intervals. There are still many who insist upon the older values and change every 3,000. This is very wasteful according to all the info available these days and the much better oils we have now.

The major benefit of switching to full synthetic is in extending the change intervals because the synthetic does not brake down as quick as fossil oils.

My manual says change the oil every 7,500 miles but I went to full synthetic Amsoil and extend the interval to 10,000 miles but I do change just the filter at the 5,000 mile mark.

I also had my used synthetic oil analyzed after 10,000 miles by a reputable lab a while back. The report came back that my used oil after 10K was still perfectly good and could easily go another few thousand miles before any notable degradation.

It is all a matter of how you use your oil and how trusting you are about the higher quality of the synthetics. The lubricating properties of the synthetics are certainly a plus and the filters we have today are much advanced from the days of old. If you can extend your change intervals to double the recommended mileage then you are doing one change for every 2 and cutting the cost of the synthetic in half. My F 250 Diesel took 16 quarts or 4 gallons and it became a real issue every time an oil change was necessary. I broke pretty close to even when buying the synthetic but I saved a lot of time under my truck doing unnecessary oil and filter changes every few months.

Synthetic gear oils would be fine except that I am more concerned with water intrusion than I am with saving any money and I will always drop the lower unit gear oil every season just to be sure there is no water coming in.

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Non-synthetics don't suffer from break-down as much as some would have us believe. They suffer from contamination. Its the contamination from the products of combustion and synthetics are not any more immune than non-synthetic oil.

I have a friend who is the fleet mechanic supervisor for a large university. He told me a long time ago that lab analysis of their fleet vehicle oil noted the oil itself was fine long after the recommended change intervals. It was the contamination of the oil that mandated the oil change.

If you go beyond the manufacturer recommended oil change interval no matter what type of oil you use, you are putting your engine at increased risk of failure.

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I am not here to argue with anyone but there is tons of info and studies on the net from some very reputable sources that completely disagree with what you and your fleet buddy believe. Fossil oil suffers most from the high heat of today's engines and this is why many manufacturers are going to Synthetic. All turbo engines are recommended for nothing but synthetic because of the high temps and high RPMs.

Keep in mind that most of our outboard motors are often running at the high end of their RPM bands and a good deal higher than most vehicle motors.

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...and concerning the contamination of those synthetics when going beyond the engine manufacturer's change intervals?

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When I had my 10,000 mile oil analyzed the report indicated "Low Contamination" and no need to change the oil but to replace the oil filter within the next few thousand miles. The filter is what removes the contaminants.

It cost $22 to have the oil analyzed and they send you back a very detailed report. I just sold the F 250 and gave the new owner the report or I would gladly email you a copy of it.

I have used synthetics in all my road vehicles for years now and they rust to pieces long before the engines or tranny's wear out. I have honestly never had an internal engine failure ever.

That said, I don't know if I would use the synthetic if I had a 4 stroke boat motor or not. My 1991 Honda Wagon has 215,000 miles on it now and runs like a top and never burns a drop of synthetic oil between changes every 8,000.

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My previous comments were based on scientific oil analysis. The fleet my friend was responsible for encompassed a variety of vehicles ranging from daily commuters to heavy equipment worth in the millions of dollars. His job was to make sure that equipment was best cared for and the information wasn't based on any personal belief. Regular oil analysis was part of maintaining that fleet and the information he shared was based on decades of scientific reports.

The byproducts of combustion that collect in engine oil and form corrosive compounds are not filtered out of the engine oil by the filter as far as I know. Maybe full sythetics offer the benfit of better corrosion protection from such compounds? I'm sure its at least claimed in the marketing literature.

Ultimately I respect each individual's choice.

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"Ultimately I respect each individual's choice."

Same here!

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One thing I do now know, synthetic is pricey, $9.50 at the Merc Dealer!!!!!

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That is the case with all of these dealer provided oils.
My Polaris ATV oil is twice as expensive at the dealer but a great deal less at my Amsoil supplier. Amsoil has an oil that meets the specs on just about any synthetic we need. Lucas is also pretty good with matching the specs.

I don't know the first thing about 4 cycle boat motors but I suspect they will have a sump and filter set up and the one place I would never skimp on is the filter.

We have kicked this exact subject around on the ATV forums for ever and the one thing that seems constant is as long as the oil you use meets the API service requirements listed on the dealer's jug it is good to use.

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I don't have a scientific source to back it up, but a common practice on new engines is to run dino oil until the engine is fully broken in and then switch to synthetic. Some believe that new piston rings may not seat properly on synthetic.

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I also am from the break it in on dino school, based on a report I read some years ago. Sorry, no link of credentials to boost my case for this. I run synth in everything and I notice is that valve trains are much quieter under all circumstances.

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I personally am a believer in synthetic oil, especially for gear lube, but I don't necessarily extend the change intervals. Regarding contamination, the oil in marine engines does not get nearly as dirty because of the environment you're running in, unlike road vehicles that pick up all kinds of crap from the air. Granted, the by-products of combustion will still contaminate the oil but overall contamination is much less in a marine engine. Note that the oil in your car will change from clear yellow to black after little use. Not so quick in a marine engine.

BTW, my opinion is that synthetic blends are a waste, including Merc's synthetic blend. With a synthetic blend, all you end up with is a poor performing synthetic. Even the many of the full synthetics out there aren't that great. Amsoil, Redline, etc. are the real deal (and pricey) but some of the other brands you buy off the shelf at the store aren't so great. The real question is whether or not the "real deal" synthetics are overkill. I honestly don't know.

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We found it pretty funny on the ATV forums that each company has their own labeled full synthetic oils at ridiculous prices. Neither Polaris, Honda or Yamaha refine or make their own oils! They buy them from companies that do make oils and put the juice in their own jugs. The only thing we could learn is that it is not Amsoil, Redline or Lucas synthetics in those jugs and they are the three most trusted names in synthetics.

I honestly believe that most of these so called contaminants we are discussing are a byproduct of burnt oil and fuel that remains in the sump and goes back through the filter. I don't remember exact numbers but the studies I have seen made a big deal that dino oil would burn at about half the temperature of the synthetics and I think it was around 600 degrees for dino and over 1200 for the synthetics. This alone would reduce contamination considerably.

We just bought 2 new Toyota vehicles and both require synthetic oils and are breaking in with it. I think the two major concerns while an engine is braking in are first the proper allowing of ample time for parts to mesh together and seat while under a standard load and second for the original oil to flush any loose manufacturing particles from the systems where they should end up in the filter or in the sump to be dumped out.

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You still change the filter at regular intervals.

John K.

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So, at how many hours do you think I should do the very first oil change in this 4 stroke Merc?

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New motor and under the Manufacturers warranty so I would absolutely follow the exact recommendations for both oil and interval of change.

I might even have the service done by a dealer just to have proof positive.