February 2025 Column How to Check Your Outboard’s Engine Oil Level... T he author reached out to the leading outboard manufacturers to find out By Capt. John N.Raguso HISTORY LESSON As we discovered in last month’s column, marine engine oil (both outboard and inboard) has a radically different chemistry compared to automotive lubricants. Marine engine oils have to handle high RPM and constant loads experienced by marine engines. Marine engines frequently operate for long periods at either idle or wide-open throttle, with the majority typically spending most of their time at 3500-to-4500 rpm. Many marine engines are cooled by lake, river or sea water so, while thermo- statically-controlled, their temperature cycling is much different. A marine engine oil has to resist shear, moisture and corrosion more than an automotive engine oil and has to have
extremely strong film strength to protect engine parts under constant stress and load. Finally, marine engines often go past their oil change window, so anti-oxidants are critical to extending oil lifespan. Engine configuration in outboard applications is much dif- ferent than in an automotive application, with the engine often configured vertically. The job of an oil in a vertically- oriented engine is even more challenging because it has to flow up and down while providing consistent protection throughout the engine. Lubricating cylinders and bearings at the top of the engine can be more difficult, and even lubricating individual cylinders, crankshaft and rod bearing journals can be challenging. Because marine engine oils have to protect against so many marine-specific things (cor- rosion, oxidation, shear, moisture) additives are much more important in a marine oil blend than in an automotive blend.
With this extreme focus on your marine engine oil’s responsibilities, it’s imperative to be sure that it’s up to the task, at the proper level and not blackened with excessive wear or contamination. This requires periodic checking, with Yamaha, Mercury and other outboard manufacturers recommending that you check your oil’s level and condition prior to every trip. While this is a great idea, most boaters rarely check their engine oil status with this degree of frequency. And why is that? It’s a real PITA to take off the cowling, start the engine, tilt the engine up and down, level the engine, check the dipstick and then reinstall the cowling, and that’s just with one engine. Multiple outboards require even more time for this basic TLC. Most folks are either“just in time”when assembling the crew for a day on the water or running late, so this very important pre-check ritual
gets put off. This is a big mistake and can lead to shorter engine life and increased problem frequency.
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