Exhaust Extension Plate Gasket – Fits Mercury 650, 800, 1150, 1250, 1350 (Replaces 27-48801)

$8.99 $14.00

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Product Details

This is a high-quality aftermarket Exhaust Extension Plate Gasket – Fits Mercury 650, 800, 1150, 1250, 1350 (Replaces 27-48801), an essential component for sealing the exhaust system in specific vintage Mercury outboard engines. It is designed for Mercury Marine 650-1350 HP (4 Cylinder) models manufactured within the 1970s–1980s serial number ranges.

This part is a direct replacement for Mercury OEM part number 27-48801 and Sierra aftermarket part 18-0344.

Provides a direct-fit installation with no modifications required.
Creates a durable seal between the exhaust extension plate and the drive shaft housing.
Engineered for use in marine gasoline engine environments.

Part Number Matrix

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

Brand	Part Number
Mercury	27-48801
Sierra	18-0344

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury engines, compatibility is determined by serial number. Please ensure your engine's serial falls within the specified range.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Mercury	650 (4 CYL.)	65.0	2-Stroke	Serial #2803562-3293183	27-48801
Mercury	800 (4 CYL.), 80 (4 CYL.)	80.0	2-Stroke	Serial #2559001-3493912	27-48801
Mercury	1150	115.0	2-Stroke	Serial #2836019-3525440	27-48801
Mercury	1250	125.0	2-Stroke	Serial #2314956-2839368	27-48801
Mercury	1350	135.0	2-Stroke	Serial #2839369-3293233	27-48801

Technical Specs

Product Type: Exhaust Extension Plate Gasket
Installation: Direct replacement
Fuel Type: Gasoline
Housing Material: Gasket material (likely composite or fiber)
Dimensions: 36.0 cm L x 20.0 cm W x 0.5 cm H
Other Technical Attributes: Exhaust extension plate to drive shaft housing seal

What’s in the Box

1 x Exhaust Extension Plate Gasket (27-48801)

Installation Notes

Ensure the engine is off and cool, and disconnect the battery for safety.
Gain access to the exhaust extension plate, removing cowlings or other components as needed.
Carefully unbolt and remove the exhaust extension plate.
Remove the old gasket completely, then thoroughly clean both mating surfaces to remove any old sealant or residue.
Position the new gasket correctly onto the drive shaft housing.
Reinstall the extension plate, ensuring it is properly aligned. Tighten bolts in a crisscross pattern to the manufacturer's specified torque to ensure even pressure.
Reassemble all previously removed components.
After reassembly, run the engine and check for any signs of exhaust or water leaks around the sealed area.

Troubleshooting & FAQ

How do I know if this gasket will fit my engine?

This gasket fits specific 4-cylinder Mercury models from 650 to 1350 HP, generally from the 1970s–1980s. Always verify your engine's serial number against the ranges listed in the compatibility table to ensure a perfect match.

What are the signs of a failing exhaust extension plate gasket?

Common signs include a noticeable exhaust leak (louder noise or fumes) from the mid-section of the outboard, water entering the exhaust housing, or potential engine overheating issues due to exhaust gas disruption.

Can I reuse my old gasket?

No. Gaskets are single-use components designed to compress and create a specific seal. Reusing an old gasket will almost certainly result in leaks and poor performance.

What is the difference between this part and the OEM Mercury 27-48801?

This is an aftermarket part engineered to meet or exceed OEM specifications for fit, form, and function. It provides the same reliable seal as the original Mercury part, offering a cost-effective solution without compromising quality.

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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