Exhaust Plate Gasket – Fits Mercury/Mariner 2.5L V6 105-220 HP (Replaces 27-991764)

$19.99 $31.00

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Product Details

This Exhaust Plate Gasket is designed for a precise fit on Mercury/Mariner 2.5L V6 105–220 HP 2-Stroke outboard motors manufactured from the late 1970s through the 1990s. It creates a critical seal between the cylinder block and the exhaust plate, preventing exhaust leaks and ensuring proper engine performance.

It serves as a direct replacement for Mercury OEM part 27-991764 and Sierra aftermarket part 18-2506-1, offering a reliable and cost-effective alternative to OEM components.

Installation Location: Between cylinder block and exhaust plate
Material: High-strength composite for durability and a reliable seal

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury	27-991764
Mercury	991764
Sierra	18-2506-1

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This gasket fits a wide variety of Mercury and Mariner V6 outboards. Verify your engine's serial number falls within the specified range for a guaranteed match.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Mercury	V-115 DFI (2.5L)	115	2-Stroke	0G960500–0T178499	27-991764
Mercury	V-135	135	2-Stroke	0G960500–0T178499	27-991764
Mercury	V-135 DFI (2.5L)	135	2-Stroke	0G960500–1B417701	27-991764
Mercury	V-135 DFI (2.5L)	135	2-Stroke	1B417702 & Up	27-991764
Mercury	V-140 (International)	140	2-Stroke	0T178500–1B226999	27-991764
Mercury	140 JET	140	2-Stroke	0G960500–0T178499	27-991764
Mercury	V-150	150	2-Stroke	0G960500–1B226999	27-991764
Mercury	V-150 (EFI)	150	2-Stroke	0G960500–0T408999	27-991764
Mercury	V-150 DFI (2.5L)	150	2-Stroke	0G960500–1B417701	27-991764
Mercury	V-150 DFI (2.5L)	150	2-Stroke	1B417702 & Up	27-991764
Mercury	V-150 EFI (2.5L)	150	2-Stroke	0T409000–1B226999	27-991764
Mercury	V-150 EFI (2.5L)	150	2-Stroke	1B227000 & Up	27-991764
Mercury	150 Pro XS (2.5L)	150	2-Stroke	1B690542 & Up	27-991764
Mercury	V-175 (EFI)	175	2-Stroke	0G960500–0T408999	27-991764
Mercury	V-175 DFI (2.5L)	175	2-Stroke	0T178500–1B417701	27-991764
Mercury	V-175 DFI (2.5L)	175	2-Stroke	1B417702 & Up	27-991764
Mercury	V-175 EFI (2.5L)	175	2-Stroke	0T409000–0T800999	27-991764
Mercury	175 PROXS (2.5L)	175	2-Stroke	1B516339 & Up	27-991764
Mercury	V-200	200	2-Stroke	5624878–0C100860	27-991764
Mercury	V-200	200	2-Stroke	0G960500–1B226999	27-991764
Mercury	V-200 (EFI)	200	2-Stroke	0G960500–0T408999	27-991764
Mercury	V-200 EFI (2.5L)	200	2-Stroke	0T409000–1B226999	27-991764
Mercury	V-200 EFI (2.5L)	200	2-Stroke	1B227000 & Up	27-991764
Mercury	110 Jet (2.5L)	110	2-Stroke	1B690542 & Up	27-991764

Technical Specs

Product Type: Cylinder Block Exhaust Plate Gasket
Material: Composite
Product Dimensions: 32 × 23 × 2 cm (12.6 × 9.06 × 0.79 inches)
Package Dimensions: 32 × 23 × 2 cm (12.6 × 9.06 × 0.79 inches)
Weight: 0.08 kg (0.18 lb)
OEM Part Number: 27-991764

What’s in the Box

1 x Cylinder Block Exhaust Plate Gasket (27-991764)

Installation Notes

Disconnect the battery and ensure the engine is cool to the touch.
Remove the engine cowling and any other components obstructing access to the exhaust plate.
Carefully unbolt and remove the exhaust plate assembly.
Remove the old gasket and thoroughly clean both mating surfaces on the cylinder block and exhaust plate. Ensure all old gasket material and sealant residue is gone.
Position the new gasket correctly on the cylinder block.
Reinstall the exhaust plate, tightening bolts to the manufacturer's specified torque in the correct sequence.
Reconnect the battery, start the engine, and check for exhaust leaks around the sealed area.

Troubleshooting & FAQ

How do I know if my exhaust plate gasket is failing?

Signs of a failing gasket include visible exhaust or water leaks around the exhaust plate, an unusual hissing sound from the engine, overheating, and a noticeable loss of engine performance or rough idling.

Can I reuse my old gasket?

No. This is a one-time-use, crush-style gasket. Once it has been compressed, it will not seal properly if reinstalled. Always use a new gasket when the exhaust plate is removed.

Is any sealant required for this gasket?

Generally, this type of composite gasket is designed to be installed dry. However, always consult your engine's official service manual, as some specific procedures may recommend a light application of a specific sealant.

What is the difference between this and an OEM gasket?

This aftermarket gasket is manufactured to meet or exceed OEM specifications for fit, material, and performance. The primary difference is the price and the fact it is not sold under the original manufacturer's brand.

My engine model isn't listed, but the part number matches. Will it fit?

If your old part has the number 27-991764, this gasket is the correct replacement. Our compatibility table is extensive but may not cover every single sub-model or local variant. The part number is the most reliable confirmation.

How often should this gasket be replaced?

The gasket should be replaced any time the exhaust plate is removed for service. It is not a routine maintenance item but should be inspected for leaks periodically as part of overall engine health checks.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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