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What are the primary differences between four-stroke automotive oil and marine oil?

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Many enterprises are curious about what makes four-stroke engine oils which are formulated for marine use and automotive applications different. While both products are developed to serve four-stroke engines, the operating environments and equipment types involved make different demands on lubricants deployed.

In this blog post, we’ll take an in-depth look at what the key differences are between marine and automotive oils for four-stroke engines. Read on to keep your knowledge base up to date.

Work rates of marine and automotive engine oils

Marine oil products are vastly different to automotive oils. This is primarily because marine applications are far more intense compared to automotive engines. The engines in automotive vehicles are not designed and constructed to operate all day long at 6,000 RPM (revolutions per minute). As a result, the automotive engine oil created to serve such systems is not formulated to provide protection at such an extreme level.

Oil specifications of marine and automotive engine oils

Engine oil for the automotive industry have specifications that follow a completely different agenda from marine oils because of the mandates, warranty items, and regulations they need to target.

Unlike automotive lubricants, marine oils are formulated and engineered to cope with harsh saltwater environments. An automotive oil doesn’t have to work in a constantly corrosive environment like boats do. As a result, marine oils must have much higher doses of additives providing anti-corrosive protection. These distinct differences are certified to meet minimum industry standards by the National Marine Manufacturer’s Association (NMMA) via the FC-W four-stroke oil registration programme.

Formulation of marine oils

Marine oils feature a different formulation to automotive oils. While both will typically employ a base product complete with an additive package that enhances or suppresses key properties in the foundation oil, the demanding operating environment of marine applications requires different additives to provide specific attributes. Furthermore, the additive pack is far more important in marine oils, often comprising a far higher percentage in the total product. For example, marine oils will be between 20% to 35% additives, while automotive engine oils contain juts 10% to 20% additives.

For instance, many leading marine oils will feature anti-foaming agents, anti-wear additives, shear-stability polymers and anti-corrosion inhibitors to deliver proper protection in a sustained high-RPM application. Additionally, they will usually include dispersants, detergents, and viscosity index improvers that either achieve or exceed the NMMA’s FC-W specification.

Four-stroke outboards must endure extreme operating conditions and the oils that serve them are specifically designed to answer the unique challenges they face. These include the issue of oil dilution, which happens sometimes when fuel from the combustion chamber leaks through worn piston rings and finds its way inside the oil crankcase, where it can cause havoc.

How are marine oils manufactured and how do they differ from four-stroke automotive oils?

Marine and automotive engines are built to run differently. To meet set fuel economy and emissions standards, an automotive engine is calibrated to operate within a fixed RPM range and rarely experiences heavy loads. For the most part, automotive engines work at low RPM. The term “cruising” is used to describe the motion of vehicles rolling along under relatively light loads. Automotive engines also work at a controlled temperature to make sure they can provide consistent fuel usage and operation.

In contrast, marine engine oils must handle high RPM and experience constant loads as is the way with modern marine engines. Maritime engines usually operate at either wide-open or idle throttle. Many are cooled by sea, river or lake water. As a result, while they are naturally thermostatically controlled, the temperature cycling they experience is far different, and in some cases, fuel dilution may be a problem. A marine engine oil must also resist corrosion, moisture, and shear more than any automotive engine oil. For this reason, it is designed to provide and an exceptionally strong film, which can coat and protect engine components under continuous load and stress.

Marine engines must often exceed their optimal oil change window. For this reason, antioxidants are a critical ingredient in formulation to extend the lifespan of oil and allow it to serve for longer within desired performance parameters.

It’s worth noting that engine configuration within outboard marine applications is also different compared to automotive applications with the engine usually configured vertically. The role of the lubricant in an engine that is vertically oriented can be extremely challenging. This is because the oil must flow both up and down to provide consistent protection to the entire engine. The most difficult parts of the engine to lubricate are the bearings and cylinders located at the top of the engine, but even lubricating individual rod-bearing journals, cylinders and the crankshaft can present substantial challenges.

For best results, always select your engine oil based on your original equipment manufacturer’s recommendation and don’t attempt to substitute the ideal lubricant with a solution not designed for an application.

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