Sierra 18-9421CAT-3 9421CAT3 4-Stroke Synthetic Blend Catalyst Outboard Engine Oil, 10W30, Gal.

Unlock Reliable Performance with Catalyst-Compatible Marine Oil

Picture this: you're out on the water, wind in your hair, engine humming smoothly as you chase the horizon. The last thing you want is a breakdown from poor lubrication or catalyst failure. That's where this 4-stroke synthetic blend outboard engine oil steps in, engineered specifically for modern marine engines demanding top-tier protection. With a 10W-30 viscosity, it flows effortlessly in cooler starts while shielding high-revving components during those long, demanding cruises.

Boat owners know the harsh marine environment—salt spray, constant vibration, and extreme temperature swings—can wreak havoc on unprotected engines. This oil tackles those challenges head-on, blending synthetic technology with proven additives to deliver peace of mind. Whether you're running a sleek outboard for fishing trips or powering a sterndrive for family outings, it keeps things running clean and efficient.

Engineered for the Demands of Today's Outboards

Modern 4-stroke engines, especially those with emission control systems, require oils that won't compromise performance or longevity. This formula rises to the occasion by meeting stringent standards for recreational powerplants, with or without catalysts. It's your go-to for outboards, sterndrives, and inboards, ensuring seamless operation across applications.

What sets it apart? A sophisticated balance of anti-wear agents, including advanced ZDDP technology, that fights metal-on-metal contact under high loads. Add in exceptional deposit control to keep pistons and valves spotless, and you've got an oil that outperforms in real-world boating scenarios—from idle trolling to wide-open throttle.

Battle-Tested Protection Against Corrosion and Wear

Nothing tests an engine like saltwater exposure and prolonged idling. This synthetic blend forms a robust barrier against corrosion, even in the most brutal conditions. It prevents the phosphorus buildup that shortens catalyst life, so your emission system stays effective longer. Plus, industry-leading wear protection means fewer worries about scored bearings or premature part failure.

• Superior rust inhibition for saltwater warriors
• Prevents pre-ignition and low-speed pre-ignition (LSPI) risks
• Maintains viscosity stability across temperature extremes
• Keeps combustion chambers clean for optimal fuel efficiency

Boaters switching to this oil often notice smoother shifts, quieter operation, and extended service intervals. It's not just lubrication—it's proactive engine care.

Ideal Match for Mercury and Beyond

If your rig runs a Mercury 4-cycle outboard calling for 10W-30, this is the precision match. But its versatility shines in any NMMA FC-W certified setup, including those with catalyst tech. Certified to exceed FC-W and FC-W Catalyst Compatible benchmarks, it delivers the reliability pros demand without the guesswork.

Pro tip: During oil changes, warm up the engine first for thorough drainage, then refill to spec. Pair it with routine filter swaps to maximize benefits. Your investment in quality oil pays dividends in resale value and trouble-free adventures.

Why Synthetic Blend Outshines Conventional Oils

Synthetic blends like this one combine the best of mineral bases with synthetic fortifiers, offering better cold-flow properties than straight conventional oils and cost savings over full synthetics. The result? Enhanced thermal stability, reduced sludge, and longer-lasting protection tailored for marine duty cycles. It's the smart choice for weekend warriors and serious anglers alike who want performance without excess.