ArticleBoatingService Repair

The Value Of Viscosity

Hunting game fish in the open ocean is a thrill and what today’s technology is capable of is truly fantastic. Sophisticated rods, reels, line and lures manufactured to incredible tolerances with precise specifications have made our fishing exploits easier and more enjoyable than ever. Outboard engine development has also surged alongside all other aspects of fishing and boating, with the latest powerhouses propelling vessels to distant waters at speeds and efficiencies greater than ever before. With this technology, the leading-edge design of modern outboards and resulting performance, regardless of manufacturer, horsepower rating or application, requires equally advanced lubricants to keep things running smoothly and efficiently.


Image 1 of 3


Fail to change your motor oil on a routine schedule and you may face a major mechanical meltdown at the worst possible time. If that happens and you’re a long distance from home, you’ll be faced with a much greater loss of time, effort and money than if you would have simply followed the manufacturer’s recommended maintenance schedule in the first place. It all boils down to controlling the incredible friction between your engine’s many internal moving parts, and recognizing that clean engine oil is the most important facet to trouble-free performance.

It all boils down to controlling the incredible friction between your engine’s many internal moving parts, and recognizing that clean engine oil is the most important facet to trouble-free performance.

By now it should be clear that modern four-stroke outboards offer significant advancements over yesteryears technology, but many boaters still operate two-strokes, which have completely different oil requirements. Two-stroke engines require oil to be carefully mixed directly with the gasoline. As fuel is injected into the motor, the oil provides lubrication. On the other hand, four-strokes feature a simplistic reservoir and pump system to distribute oil throughout the motor, very much like your automobile. While the effective lifespan of engine oil varies greatly depending on application, usage and whether petroleum based or synthetic, most outboard engine manufacturers recommend changing engine oil regularly, most as often as every 100 hours.

Whether it’s an electronic fuel injected four-stroke or low-pressure direct injection two-stroke, your engine’s manufacturer also has particular recommendations for engine oil, but for many people changing their oil is something beyond their capabilities. While changing engine oil can be easily accomplished if you are even slightly mechanically inclined, along with regular oil changes preventative measures also include the replacement of fuel filters, lower unit oil, water pumps, seals, grease fittings and spark plugs. All of this is usually too much for a basic DIY project, which is why most owners choose the service provided by trained and certified professionals, especially when dealing with triple and quad engine applications.

While routine maintenance is a wonderful thing, it is imperative that you’re feeding your motor the correct oil. Stroll down the aisle of your local boating accessory store and you’ll see an overwhelming amount of oil variations…10W-30, 5W-30, 20W-40… what does it all mean? Motor oils are rated by viscosity, with modern lubricants utilizing some sort of multi-viscosity synthetic blend. When it comes to the number ratings, oil that has a lower number is thinner and flows easier. This first measure of viscosity is crucial to the ongoing survival of a marine engine during the first few seconds of cold operation. Engine damage can occur during startup if the engine oil is too thick and cannot flow freely across all internal moving parts.

Thicker oils have a higher number rating. As an example, Mercury Marine’s 300 HP Verado utilizes 25W-50. You just learned the number 25 indicates that the oil will have the properties of a 25-weight under a cold start, but will perform like a 50-weight at operating temperature. This is an ideal blend for the powerful supercharged 300 Verado, which reaches extreme temperatures while providing industry leading power and performance.

If you own and operate a late model motor, it’s very likely you use synthetic oils because of required efficiency and emission standards. Synthetics are a blend of chemical compounds that are artificially made. In addition to helping engines run cleaner, they also help reduce wear and tear to maximize engine life.

If you change your oil yourself, or if you purchased a pre-owned boat and aren’t sure what oil to use, the best strategy is to refer to the manufacturer’s recommendation. This guideline is based on viscosity requirements, temperature and performance ratings. It’s also important the oil is certified from the Society of Automotive Engineers (SAE), the American Petroleum Institute (API) or National Marine Manufacturers Association (NMMA). Failing to follow the manufacturer’s recommendation could not only damage your engine, but could also void an existing warranty.

Oil Analysis

If you’re not already on a routine schedule of oil changes, start now. There is absolutely nothing worse than being out of commission and having to deal with costly repairs that could have been avoided.

The pre-owned boat market is saturated, but there are some diamonds in the rough if you’re willing to sort through the mess. If you’re looking into purchasing a pre-owned boat, marine surveyors recommend an engine oil analysis and compression test. An engine oil sample can reveal critical information regarding the health of the engine(s) and oil, and ingress of contaminants to diagnose potential issues and prevent expensive repairs.