Sierra 18-8382 Lower Unit Seal Kit - Replaces Mercury 26-816575A4 - Fits 200/225/250 HP EFI/Optimax Outboards

The Sierra 18-8382 Lower Unit Seal Kit is a gearcase seal kit for Mercury and Mariner outboard motors, designed to restore a watertight, oil-tight seal in the lower unit during a gearcase rebuild or seal replacement service. It is built as a direct equivalent to Mercury Marine part 26-816575A4, giving outboard owners and marine technicians a way to service the lower unit without sourcing the original Mercury part. Using the correct seal kit for the specific horsepower and serial number range is important, since Mercury outboards saw multiple lower unit casting and seal revisions across production, including the "C-3 Casting" variant covered by this kit.

This kit covers a range of Mercury 200 HP, 225 HP, and 250 HP outboards, including EFI and Optimax DFI configurations, matched to specific serial number breakpoints. Confirm your engine's horsepower, configuration (EFI or Optimax DFI), and serial number against the fitment list below before ordering, since lower unit seal kits are not interchangeable across all serial ranges.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-8382
• Category: Mercury Outboard Gearcase Seal Kit
• Weight: 0.15 pounds
• Product Dimensions: 0.75 x 6 x 7.5 inches
• UPC: 808282200428
• Exterior Finish: Machined
• Replaces (OEM): 26-816575A4

Fitment

• 200 HP (T801000 & Up)
• 200 HP Optimax DFI (G438000 & Up)
• 225 HP EFI (G438000 & Up)
• 225 HP Optimax DFI (G590000-G960499)
• 250 HP EFI (G438000 & Up)
• Models with C-3 Casting: 200 HP Optimax DFI (G386496-G437999)
• Models with C-3 Casting: 225 HP (D280813-G437999)
• Models with C-3 Casting: 225 HP EFI (G129222-G437999)
• Models with C-3 Casting: 250 HP EFI (G129222-G437999)

Replaces (OEM)

• 26-816575A4

Frequently Asked Questions

What does the Sierra 18-8382 Lower Unit Seal Kit fit? It fits Mercury/Mariner 200 HP (T801000 & Up), 200 HP Optimax DFI (G438000 & Up), 225 HP EFI (G438000 & Up), 225 HP Optimax DFI (G590000-G960499), and 250 HP EFI (G438000 & Up) outboards, plus C-3 Casting models: 200 HP Optimax DFI (G386496-G437999), 225 HP (D280813-G437999), 225 HP EFI (G129222-G437999), and 250 HP EFI (G129222-G437999).

Is Sierra 18-8382 the same as Mercury 26-816575A4? Yes, Sierra 18-8382 replaces Mercury Marine part number 26-816575A4 and is built to match its fit and function in the lower unit.

How much does this seal kit weigh? The Sierra 18-8382 Lower Unit Seal Kit weighs 0.15 pounds.

What are the dimensions of the 18-8382 seal kit packaging? The kit measures 0.75 x 6 x 7.5 inches as packaged.

Will 18-8382 work on any Mercury 200 HP outboard? No, it is matched to specific serial number ranges. For a standard 200 HP it covers T801000 & Up, and for 200 HP Optimax DFI it covers G438000 & Up (or G386496-G437999 on C-3 Casting models), so the engine's serial number must be checked before ordering.

What is C-3 Casting and why does it matter for this kit? C-3 Casting refers to a specific lower unit casting revision on certain Mercury 200-250 HP outboards; the Sierra 18-8382 kit lists separate serial number coverage for C-3 Casting models (for example 225 HP D280813-G437999) since those units use a different seal configuration than later castings.

Does the 18-8382 kit cover 225 HP EFI and 225 HP Optimax DFI the same way? No, they have different serial number ranges: 225 HP EFI is covered at G438000 & Up (or G129222-G437999 on C-3 Casting models), while 225 HP Optimax DFI is covered at G590000-G960499.

What finish does the Sierra 18-8382 seal kit have? The components in the 18-8382 kit have a machined exterior finish.

Is this a genuine Mercury part or an aftermarket replacement? The Sierra 18-8382 is an aftermarket seal kit manufactured by Sierra as a replacement for Mercury Marine part 26-816575A4, not an OEM Mercury-branded part.

What UPC is associated with the Sierra 18-8382 seal kit? The UPC for the Sierra 18-8382 Lower Unit Seal Kit is 808282200428.