Customer Service
+1 888 812 6287
Required for fitment review to confirm compatibility.
The SEI SE206 Mercury V6 lower unit is a new aftermarket replacement gearcase for selected Mercury 2.0L, 2.4L and 2.5L V6 outboards using a 4¾-inch gearcase housing.
Four configurations are available, combining 1.87:1 or 2.00:1 gear ratios with a 20-inch L or 25-inch XL driveshaft. The SE206 is intended for standard/right-hand-rotation applications.
The SE206 replaces most—but not every—Mercury gearcase within these displacement families. Horsepower or displacement alone cannot confirm fitment. Before ordering, verify your complete engine serial number, existing gear ratio, driveshaft length, rotation and gearcase diameter.
Before shipment, the selected gear ratio, driveshaft length, SEI part number and customer-supplied engine information are reviewed together. If additional information is required to evaluate fitment, Mariners Warehouse will contact the customer before shipment.
The SE206 must be filled with the correct marine gear lubricant before operation. Follow the supplied break-in instructions and SEI installation procedure. Installation should be completed by a qualified marine technician familiar with Mercury outboard gearcases.
| Specification | Mercury SE206 Outboard Lower Unit | 2.0L, 2.4L & 2.5L | SE90-206 |
|---|---|
| Product | New aftermarket replacement gearcase |
| Manufacturer | SEI Marine |
| Product family | SE206 |
| Parent part number | 90-206 |
| Engine family | Selected Mercury 2.0L, 2.4L and 2.5L V6 outboards |
| Gearcase diameter | 4-3/4-inch bullet |
| Rotation | Standard/right-hand only |
| Ratio options | 1.87:1 and 2.00:1 |
| Gear teeth | 15/28 for 1.87:1; 14/28 for 2.00:1 |
| Shaft options | 20-inch L and 25-inch XL |
| 20-inch 1.87 SKU | 90-206-A20 |
| 25-inch 1.87 SKU | 90-206-A25 |
| 20-inch 2.00 SKU | 90-206-B20 |
| 25-inch 2.00 SKU | 90-206-B25 |
| Fitment basis | Engine serial number, existing ratio, shaft length and gearcase diameter |
| Major exclusions | 4-1/4-inch cases, Sport Master, Torque Master, CLE and other high-performance gearcases |
Choosing the correct Mercury V6 lower unit for a 2.0L, 2.4L or 2.5L outboard requires more than matching the engine’s horsepower.
First, confirm that the existing gearcase has a 4¾-inch bullet diameter. The SE206 does not replace the smaller 4¼-inch housing or a Sport Master, Torque Master, CLE or other high-performance gearcase.
Next, match the existing gear ratio. SE206 configurations are available in 1.87:1 with a 15/28 gear set and 2.00:1 with a 14/28 gear set. Installing a different ratio can affect engine RPM, acceleration and multi-engine synchronization.
Then confirm whether the outboard requires a 20-inch L or 25-inch XL driveshaft. Do not determine this from the boat’s advertised transom height alone.
Finally, provide the complete engine serial number. The serial number helps identify configuration changes that horsepower, displacement and model year may not reveal. If any of these details are uncertain, request a fitment review before placing the order.
Use CTRL + F or search below to find your engine model
Loading compatibility data...
No results found. Please try a different search term.
Purchased the SEI SE206 (1.87:1 ratio, 20-inch shaft) for my 2004 Optimax. Mariners Warehouse customer support helped me verify fitment using my engine serial number before ordering, which gave me peace of mind. The unit arrived double-boxed with zero damage. Installation went smoothly, and after following the 10-hour break-in period strictly, it runs quietly and shifts crisp.
Ordered the SE206 lower unit with the 25-inch XL shaft for a 2001 Mercury 200 HP EFI. Packaging was top-notch with thick foam inserts protecting the drive shaft and skeg. Everything lined up perfectly with the existing mounting studs and shift shaft connection. I've put about 35 hours on it in saltwater so far without a single issue.
Replaced a damaged factory lower unit on my 1999 Mercury 175 HP V6. The SE206 fitment assistance team answered all my questions regarding gear ratios (1.87:1). The only thing future buyers should keep in mind is to follow the break-in instructions to the letter and change the gear lube after the first 10 hours—you will see light metal dust, which is normal for gear seating.
Bought the standard 20-inch SEI SE206 lower unit for my 2005 Mercury 135 HP DFI. Shipping was fast, taking only three business days. The finish on the unit looks factory quality, and performance on the water matches OEM specs perfectly. Highly recommend confirming your shaft length and rotation type prior to placing your order.
Replacing the lower unit on a 2002 Mercury 225 HP EFI can be daunting, but Mariners Warehouse made it straightforward. The SE206 counter-rotation unit matched my twin-engine setup exactly. Packaging was secure, hardware alignment was spot on, and the 3-year fault-free warranty provides fantastic peace of mind for saltwater boating.
Need Help?
Finding the right replacement part shouldn't be frustrating. If you can't locate the marine part you need, our experienced support team is here to help. Whether you have a part number, engine model, or simply need expert guidance, we'll help you find the correct replacement so you can get back on the water with confidence.
Trusted by 50,000+ boat owners across the USA
Our team has years of experience in marine parts.
We respond quickly to get you the help you need.
We make sure you get the right part the first time.
Access to 50,000+ marine parts & accessories.
Thanks for subscribing!
This email has been registered!
