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Required for fitment review to confirm compatibility.
The SEI SE216 Mercury 3.0L Lower Unit is a premium aftermarket standard-rotation replacement gearcase designed for select Mercury 3.0L V6 outboard engines with serial numbers 1B504989 and lower. Engineered for smooth power transfer and long-lasting durability, it is available in 1.75:1 and 1.62:1 gear ratios with specific one-piece or stub-shaft driveshaft configurations.
Important Fitment Note: Engine horsepower or displacement alone is not enough to confirm fitment. Please verify your full engine serial number, existing gear ratio, driveshaft length, spline count, and rotation before purchasing. Does not replace Torque Master, Torque Master 2, or Sport Master gearcases.
Before shipment, the selected SEI SE216 Mercury 3.0L lower unit configuration is reviewed against the engine information submitted with the order. To support this review, provide the complete engine serial number and select the correct gear ratio, rotation, driveshaft length and spline configuration.
The information reviewed should include:
| Specification | Mercury SE216 Outboard Lower Unit | 3.0L Standard Rotation | SE90-216 |
|---|---|
| Product | New aftermarket replacement gearcase |
| Manufacturer | SEI Marine |
| Product family | SE216 |
| Engine family | Selected Mercury 3.0L V6 outboards |
| Serial range | 1B504989 and below |
| Rotation | Standard/right-hand only |
| Gear ratios | 1.75:1 and 1.62:1 |
| One-piece driveshaft | 13-spline configurations |
| Shaft options | 20-inch, 25-inch and selected 30-inch configurations |
| Stub-shaft options | Available for original 8-spline applications; compatible OE upper driveshaft required |
| Water-tube coupling | Included for serial number 0G438000 and higher |
| Early coupling requirement | Below 0G438000, reuse the existing coupling or use SEI 96-116-12K |
| Exclusions | Does not replace Torque Master, Torque Master 2 or Sport Master |
| Current SKUs | 90-216-A20, 90-216-A25, 90-216-A30, 90-216-AS, 90-216-B20, 90-216-B25 and 90-216-BS |
Choosing a Mercury 3.0L lower unit requires more than matching the engine’s displacement or horsepower. Start with the complete engine serial number. The SEI SE216 is intended for selected Mercury 3.0L V6 applications with serial number 1B504989 and below, but the original gearcase type must still be confirmed.
Next, verify whether the existing gearcase is standard or counter rotation. The SE216 is a standard/right-hand lower unit; selected counter-rotation applications use the SE218. You must also match the original 1.75:1 or 1.62:1 gear ratio.
Finally, identify the driveshaft arrangement. The regular SE216 variants use a 13-spline one-piece driveshaft in the listed shaft length. An original 8-spline setup requires the appropriate Stub/Alpha variant and a compatible OE upper driveshaft. Do not use the SE216 to replace a Torque Master, Torque Master 2 or Sport Master gearcase.
If any of these details are uncertain, submit the engine serial number before placing the order.
Use CTRL + F or search below to find your engine model
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The product information made it easy to understand which SEI SE216 lower unit configuration was needed for a 2014 Mercury 150 HP FourStroke application. The 1.92:1 gear ratio, 20-inch shaft length, and serial-number verification were clearly explained. Buyers should verify every fitment detail instead of ordering by horsepower alone.
I appreciated that the SEI SE216 lower unit options clearly specified compatibility with newer Mercury FourStroke engines. The 25-inch XL shaft, 1.85:1 gear ratio, and engine serial-number guidance made the selection process much clearer. Confirming the exact gear ratio before ordering is essential.
The SEI Mercury SE216 lower unit page clearly detailed the mounting stud patterns and drive shaft length options for my 2017 Mercury 175 HP. The 20-inch, standard rotation setup was simple to identify. The fitment warnings and break-in reminders were far more helpful than a basic catalog listing.
The most important detail for this Mercury SE216 replacement lower unit was matching the 1.92:1 gear ratio. The page made it easy to compare engine horsepower ranges and shaft lengths. I highly recommend checking the original unit's gear ratio and complete engine serial number before placing an order.
The SE216-specific product guidance helped distinguish this unit for higher horsepower Mercury FourStroke models. The packaging arrived double-boxed with secure foam, protecting the shaft and skeg. The unit bolted right up to my 2019 Mercury 225 HP, and the 10-hour break-in went smoothly without any issues.
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