What type of lower unit fluid should I use?
Choosing the Right Lower Unit Fluid: A Guide
Proper lower unit fluid is crucial for the longevity and performance of your outboard motor. While some may suggest different fluids based on horsepower, the best practice is to always use a full synthetic lower unit fluid.
Here’s why:
- Superior Protection: Synthetics offer superior resistance to water contamination, extreme temperatures, and high pressures encountered in modern outboard motors. This translates to better protection against wear and tear, corrosion, and foaming.
- Enhanced Performance: Full synthetics provide smoother gear operation, improved fuel efficiency, and reduced noise levels.
- Extended Service Life: Their robust formulation allows for longer service intervals between fluid changes, saving you time and money.
Don’t be misled by the size of your motor. Even smaller outboards with lower horsepower operate under significant stress. Their compact lower units can be particularly susceptible to fluid breakdown, making the use of high-quality synthetics even more critical.
What to Look For:
- GL-5 Rating: Ensure the fluid meets the GL-5 specification. This indicates it has the necessary extreme-pressure (EP) additives to protect gears under heavy loads.
- Marine-Specific Formulation: Choose a fluid specifically designed for marine applications. These fluids are formulated to resist water intrusion and provide optimal performance in saltwater environments.
Joe’s Summary: It’s best to go with a full synthetic lower unit fluid regardless of horsepower. The smaller lower units have a small capacity and can break fluid down just as easily as the larger units. High horsepower units definitely need the sheer strength of the best synthetics. Any fluid meeting a GL5 rating should work just fine.