Adapter Plate/Block Gasket – Fits Mercury/Mercruiser 135-150 HP EFI Outboards (Replaces 27-8M0057703)

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Product Details

This high-quality Adapter Plate/Block Gasket is engineered to fit Mercury Marine 135-150 HP EFI 4-Stroke outboards from the 2000s and later, with specific compatibility determined by the engine serial number. It provides a reliable, precision-cut seal between the adapter plate and the engine block, essential for preventing leaks and maintaining peak engine performance.

This part is a direct replacement for Mercury Marine and Quicksilver part number 27-8M0057703.

Engineered as a direct fit for straightforward installation.
Designed for use with gasoline-powered marine engines.
Constructed from durable, high-quality composite gasket material to ensure a lasting seal.

Part Number Matrix

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

Brand	Part Number
Mercury Marine	27-8M0057703
Quicksilver	27-8M0057703

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury Marine engines, it is critical to verify your engine's serial number against the listed ranges to guarantee correct fitment.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	150 HP EFI	150	4-Stroke	1B905505 & Up	27-8M0057703	-
Mercury	150 HP EFI Pro XS	150	4-Stroke	2B550139 & Up	27-8M0057703	-
Mercury	150 HP EFI SeaPro	150	4-Stroke	2B139139 & Up	27-8M0057703	-
Mercury	135 HP EFI	135	4-Stroke	2B131942 & Up	27-8M0057703	-

Technical Specs

Product Type: Adapter Plate/Block Gasket
Installation: Direct fit replacement
Fuel Type: Gasoline
Housing Material: Gasket material (likely composite)
Dimensions: 30.5 × 34.5 × 1.0 inches
Weight: 0.44 lb (0.199 kg)
GTIN: 745061894341

What’s in the Box

1 x Gasket Adapter Plate/Block (27-8M0057703)

Installation Notes

Ensure the engine is off and cool, and disconnect the battery as a safety precaution.
Gain access to the adapter plate by removing any necessary engine components.
Carefully take off the old gasket. Thoroughly clean both mating surfaces to remove all old gasket material, sealant, and debris.
Place the new gasket into position, ensuring it is correctly aligned.
Reinstall all engine components in reverse order of removal. Tighten all fasteners to the manufacturer's specified torque values and in the recommended sequence.
Once assembly is complete, reconnect the battery, start the engine, and inspect carefully for any signs of water or exhaust leaks.

Troubleshooting & FAQ

How can I confirm this gasket fits my specific Mercury outboard?

The most reliable way is to match your engine's serial number to the ranges listed in the Engine & Model Compatibility table. While your model may be listed (e.g., 150 HP EFI), Mercury uses serial numbers to track mid-year production changes. If your serial number is not in the specified range, this part may not fit.

What are common signs of a failed adapter plate gasket?

Symptoms of a faulty gasket include external water leaks, engine overheating, loss of power, or water in the engine oil. Any of these signs warrant an immediate inspection to prevent severe engine damage.

Should I use sealant when installing this gasket?

This gasket is typically designed to be installed dry. Applying sealant can sometimes interfere with a proper seal unless explicitly required by your engine's service manual. Always refer to the official service manual for your specific engine model for the most accurate installation procedures.

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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