Mercury Introduces New Four-Stroke Oils

The new Mercury 25W-40 four-stroke oil formula features a proprietary additive package and is rated for both outboard and inboard engines.

19th June 2014.
By Charles Plueddeman

Mercury Marine says it spent the last five years developing a new line of four-stroke marine oils, featuring three formulas designed specifically for outboard and inboard/sterndrive engines. The two key four-stroke oils in the product line have a 25W-40 viscosity rating, and are produced with either a semi-synthetic or straight mineral-base stock formula. The third oil in the lineup is a 10W-30 mineral-base stock oil intended for use in rope-start outboards because it’s easier to pull over in a cold engine… call it duck hunter’s oil.

A photo of three bottle of Mercury Marine oil.

Mercury’s new motor lube lineup is made up of three different types of oil, including semi-synthetic and conventional.

The new oil is National Marine Manufacturers Association FC-W certified, and the 25W-40 blend can be used in any marine engine, including Verado outboards, except pre-2007 “Gen I” Verado motors. These particular engines should still be filled with Mercury 25W-50 synthetic Verado oil. I was told that this is because Mercury simply doesn’t have a Gen I Verado available to use for oil testing, and thus can’t yet certify the new oil for those motors. These three oils replace six different bottles that used to line a Mercury dealer’s shelves.

The two best ways to prevent engine wear are to use a high-quality base oil combined with a high-tech set of anti-wear additives. Knowing this, Mercury chose to develop an oil without using viscosity modifiers. A viscosity modifier is an oil additive that helps an oil maintain viscosity as temperature changes. But when these modifiers do their work, they also “stretch.” When this happens they become more susceptible to shear and the viscosity goes away. This shearing plays a huge factor in marine engines, which spend a lot of time running at high rpms and under tremendous load, degrading the oil’s ability to lubricate the engine. By not using these modifiers, Mercury is ensuring its oils would be as shear-stable as possible.

Mercury says that in a leading high-temp, high shear test (ATSM D-6278), its 25W-40 semi-synthetic was 34 percent better than marine industry FC-W minimum requirements. Additional testing (ASTM D-445) showed Mercury’s 25W-40 maintained 99.4-percent of its viscosity. What this all means is that from a lubrication standpoint, Mercury 25W-40 lubricates the same the first time you start your engine up as it does the twentieth time or fiftieth time and provides the best possible protection for any marine engine.

Mercury says the mineral 25W-40 oil is “good,” but the semi-synthetic is “best” and offered additional shear protection at the most demanding conditions. If you run hard, the semi-synthetic is the way to go. Both oils are superior to any Mercury has offered previously.

New Mercury Oil Change Kits

If you own a Mercury motor and change your own oil, here’s a handy idea that will make maintenance easier: Mercury has developed four new and convenient oil change kits that contain all the components needed to change the oil in a Mercury outboard engine. So instead of standing at the parts counter to collect the right oil, filter, and drain plug gasket, you can just grab a box off the shelf and get to work. It’s like a Happy Meal for the DIY outboard owners. Each kit includes: Mercury 25W-40 marine engine oil, a Mercury oil filter, a drain plug seal, a drip tray (if required), and complete instructions printed right on the box.

Mercury's oil change kits.

Mercury is also introducing a set of handy oil-change kits that include oil, a filter, drain plug, and everything else needed for a DIY oil change.

The kits are put together for specific engine families: 15/ 20 HP CARB Oil Change Kit (P/N 8M0081914); 25/30 HP EFI Oil Change Kit (P/N 8M0081915); 40/50/60 HP EFI Oil Change Kit (P/N 8M0081916) and 75/90/115 HP EFI Oil Change Kit (P/N 8M0081917). Retail prices range from around $22 to $60. Mercury has determined that owners of larger outboards are either not handy, or don’t care to twist a wrench, so the kits stop at 115 horsepower.

For more information visit Mercury Marine.

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About the author:

Charles Plueddeman

Charles Plueddeman is's outboard, trailer, and PWC expert. He is a former editor at Boating Magazine and contributor to many national publications since 1986.

8 thoughts on “Mercury Introduces New Four-Stroke Oils

  1. We purchased a lund/60hp mercury in 2009 from Temagami marine ,Ont and very pleased.I have noticed. If the boat is not used for several days ,when first started(cold) a noticeable amount of blue smoke exits the exhaust.I haveused mercury’s synthetic oil 20w40 since the first oil change.Is there a problem and solution.We have app 390hrs on the motor.Tks Andre

  2. A “noticeable” amount on start-up is not surprising. As long as it clears up after the motor’s warm and isn’t thick enough to raise a red flag, I wouldn’t worry about it.

  3. Hello Charles.
    Just purchasing a 2015 20hp 4 stroke merc..
    When would you change over to a synthetic oil. And I quess thats assuming that the breakin period is done with the conventional mineral oil..
    Thanks Cheers Hans

  4. Hi Hans – Charles says to follow the instructions in your owners manual regarding the initial oil change interval, and then you’re good to use either the syn-blend or mineral-based 25W-40. Merc tells us that the advantages of the syn-blend formula – enhanced durability in high-heat situations – is mostly aimed at high-horsepower Verado motors. So you’ll be well-protected with the mineral-based formula. But there’s nothing wrong with using the syn-blend. Note that if your 20 is a rope-start model, the new Mercury 10W-30 formula was designed for your motor. Its lighter “W” viscosity makes it easy to pull over on cold starts, and Merc says it really makes a difference.

  5. hello Charles I was wondering should I put that 25w-40 oil or 10w-30 in my 2013 50hp mercury. Im being told two different things..

  6. Christopher – Charles says his next column will cover this topic, as it’s caused some confusion among outboard owners. Here’s a sneak-peek that should answer your question:
    This advice, straight from Mercury headquarters:
    1. Always follow the oil spec in your owner’s manual, however…
    2. The new Mercury 25W-40 oil is great for any 4-stroke Mercury engine, and has a new base-stock formula and additive package that makes it superior to the previous Mercury oil formula. This new oil was designed to replace any previous Merc oil in any 4-stroke outboard or sterndrive EXCEPT for first-generation Verado outboard, which should still use the 25W-50 semi-synthetic oil. I would use this 25W-40 in a 50-hp Merc outboard.
    3. Mercury does recommend using its 10W-30 oil in outboard with rope starting, because it’s easy to pull over a cold motor with the lighter-viscosity oil. This application is really the only reason Mercury also offers the 10W-30 oil.

  7. Mercury 60 4 stroke. 25-40 oil, Merc filters On oil change Motor immediately blows oil past the rubber seal with a pop. 2 qts of oil in 60 seconds. I suspect the oil filter threaded rod is not perfectly square to the block. Motor is 2005 I just bought it and had a problem with the oil discharging, When I changed the oil I see the old filter is slightly bent at the flange like it was cross threaded. Any suggestions? Is it possible that the oil pump is pumping too much pressure? Thanks Doug.

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