4-stroke outboard oil got you stumped? You are non alone. A question from a boats.com reader prompts me to address some conventional oil wisdom that'due south probably shared by many boaters. The reader has a new Mercury four-stroke outboard that's due for its initial oil alter. Is information technology ok, he wonders, to fill the crankcase with the new Mercury 25W-40 Constructed Alloy oil, bold that the motor had been shipped from the manufacturing plant with "break in" oil? The short answer is yes—become ahead and apply the new Mercury oil. For the longer reply, read on.

outboard oil

Make certain your outboard is filled with an FC-W marine oil that matches the viscosity and spec listed in the owner's transmission.


Burglary Oil


A generation or two agone, engines were factory-filled with a special oil that independent an actress dose of detergent and other additives that helped new engine parts, peculiarly bearings and piston rings, clothing in together. The metallic debris from this "break in" would be carried abroad by the burglary oil and flushed from the engine on that kickoff oil change. But that was earlier the advent of computer-controlled machine tools, and the very close tolerances of mod engines.

"In nigh cases the form, fit, and part of new engine parts is of sufficiently adept quality surface finish, and good tolerance dimensionally, that it is not necessary to break-in new hardware," says Mercury oil specialist Frank Kelley.

Co-ordinate to Kelley, new motors coming from the manufacturing plant in Addicted du Lac are filled with the aforementioned 25W-40 mineral Mercury oil nosotros can buy in a canteen. Engines smaller than 50 HP manufactured for Mercury in Japan are filled with a 10W-30 oil that's composite in Japan. The use of a special burglary oil is a practice that has mostly fallen by the wayside.

With a brand-new engine, you lot still desire to follow whatever operating restrictions during the start hours of use, such every bit limiting RPM and using variable throttle settings, as described in the owner'south manual. And don't delay that initial oil change.

"Even with a mod engine and oil, it's critical not to over-shoot that initial oil modify," said David Meeler, Yamaha marine product data manager. "Think of it as the first pit stop of a long race. For Yamaha outboards that'south at 20 hours, and draining that oil will get any possible droppings out of the engine. The dealer tech will also alter the gearcase lube and check the magnetic tip of the plug for debris larger than just powder. And so if at that place'southward an issue, it can be dealt with immediately."

Switching to Synthetic Oil


All modern engines are compatible with total-synthetic and synthetic-blend oils, co-ordinate to Kelley, and information technology's besides okay to switch from mineral-based to constructed oil and back again as long equally the oil ever meets the viscosity and service specs for that engine, which are detailed in the owner's manual. In fact, many modern oils are a blend of mineral and constructed base stocks.

"In the early days of synthetic-base oil technology (the 1970s), those oils had poor seal swell characteristics and they did not solubilize the additives a well equally mineral oils," said Kelley. "It was possible to become into issues with seals and gaskets, and with additive dropout and sludge if you switched back and forth. Today the synthetic-base of operations oils are better fabricated and specific additives promote good seal swell and condiment solubility when synthetics are used, so these kinds of problems are much less probable to occur. It's too perfectly acceptable to apply current synthetic-blend oil in older engine products."

outboards

The new 25W-40 Mercury oil formula is offered in standard and a more than-durabile semi-constructed blend format. The 10W-xxx is a better selection for rope-commencement outboards.


Who Needs Synthetic Oil?


Marine engine manufacturers offering a choice of mineral-based and constructed-blend or full synthetic oils. Again, you want to outset follow the guidelines of the owner's manual regarding oil specification. There have been a few engines, such as the get-go-generation Mercury Verado outboards, that required a specific synthetic-blend oil. In almost cases, however, mineral-based oil is adequate.

The benefit of a synthetic-alloy oil is generally related to durability–information technology will hold up better in the nearly challenging conditions, such as long runs under load at high speed.

"Our total-constructed Yamalube marine oil is really intended for the loftier-operation customer," said Meeler. "The VMAX SHO owner and some of our 4.2 Offshore owners, who actually run their motors hard for an extended period of time. It'due south also a practiced choice for the F115 and F70 motors, which can be run upward to 6300 rpm."

Trolling in cold h2o might really be the toughest duty your outboard oil will ever run into. During extended trolling an outboard may not accomplish normal operating temperature and even with modern fuel injection and engine controls, unburned fuel in the combustion sleeping accommodation can condense and migrate by piston rings and contaminate engine oil, a situation engineers call "fuel dilution." When the motor next reaches its operating temp, that fuel should evaporate every bit the oil gets hot. But if you troll with a kicker and stow it away to run with a main motor, the oil in the small motor may stay contaminated with fuel. Synthetic oil is more tolerant of contamination past fuel and water condensation. Only it'due south a good idea to get that kicker upwards to temp once in awhile.

The constructed oils costs 25- to l-percent more than mineral-based oil, but we're talking about a deviation of perhaps $7.00 for a gallon jug. Given the price of a new outboard, even a little twenty HP motor, why non utilise the best oil yous tin buy?

For more than information visit Mercury Precision Lubricants and Yamalube.

Written by: Charles Plueddeman

Charles Plueddeman is Boats.com'due south outboard, trailer, and PWC expert. He is a sometime editor at Boating Magazine and contributor to many national publications since 1986.