Skip to main content

4-stroke oils certified for marine use

New 4T designation ensures they meet specifications for the high rpm, corrosive marine

The bar finally has been set for 4-stroke marine oils.

The national trade association for boatbuilders and engine manufacturers approved a new certification program, currently dubbed 4T, under which newtechnology outboard and sterndrive oils will be tested to ensure they meet minimum specifications for use in the highrpm, corrosive marine environment.

The oils will carry a “4T” designation on their labels.

The 4-stroke marine oil certification program applies standards similar to the National Marine Manufacturers Association’s successful TC-W3 benchmark for 2-stroke marine oils, says Geoff Kilburn, retail products manager for Mercury Marine.

There are differences between oils designed to run in automobile engines and 4-stroke outboards. For one thing, Passenger Car Motor Oil-certified products don’t contain rust inhibitors and won’t pass the 4T certification, according to Claude von Plato, national manager of Yamaha’s parts and accessories division.

Because the Environmental Protection Agency is mandating longer catalytic converter warranties, the automotive industry is formulating automobile oils with less ZDP (zinc dialkyl dithiophosphate), an anti-wear agent particularly effective in high-load areas, such as those experienced routinely in boating, von Plato says. Yamaha’s 4- stroke Yamalube, for example, contains twice the ZDP of forthcoming SM category automotive oils, he notes.

The committee also added a corrosion test, an area not covered by the PCMO standard and important for marine oils, he says.

“There will be a significant difference between a 4T oil and anything you buy at Pep Boys,” says von Plato. He says the program gives boat owners a way to judge what oil they should be using.

“We think it’s great,” says Mercury’s Kilburn, “because sometimes the consumer is unaware and can be doing harm to their engine without even knowing.”

In addition to highlighting differences between automotive and marine oils, 4T certification will tell boat owners that the product they choose contains all the necessary additives to perform under marine conditions.

“If you want to make oil cheap, remove the additives,” says von Plato. He says it is possible for aftermarket companies to continue removing additives until their oils just pass the tests.

Von Plato and Kilburn both recommend sticking with your engine manufacturer’s branded oil. Von Plato adds that the market for 4-stroke outboard oil isn’t very large, and he doesn’t expect much aftermarket activity in the segment.

Kilburn recommends other 4T-certified oil as a second choice. “I fully expect competitive companies to come out with [4T] qualified oils,” he says.

Certified oils will be listed on the NMMA Web site ( as they are registered, says NMMA vice president of engineering standards Tom Marhevko