Cylinder Block to Baffle Plate Gasket – Fits Mercury/Mariner 20-200 HP Outboards (Replaces 27-78411)

$10.50 $16.00

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Product Details

This aftermarket Cylinder Block to Baffle Plate Gasket is engineered for use between the cylinder block and baffle plate on various Mercury and Mariner outboard engines. It is designed to fit models ranging from 20 HP to 200 HP across multiple model years.

This part is a direct replacement for OEM part numbers Mercury/Mariner 27-78411 and 27-45088, and it also cross-references with aftermarket parts Sierra 18-0373 and GLM 31970.

Designed for direct OEM-spec installation.
Provides a crucial seal to prevent leaks between the cylinder block and baffle plate.
Compatible with a wide range of HP ratings and engine serial numbers.

Part Number Matrix

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

Brand	Part Number
Mercury/Mariner	27-78411
Mercury/Mariner	27-45088
Sierra	18-0373
GLM	31970

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Brand	Model	Rated HP	OEM Part No.	Notes
Mercury/Mariner	200	200	27-78411	Serial: 4709593 & Up
Mercury/Mariner	200	200	27-78411	Serial: 7098523 & Up
Mercury/Mariner	200	200	27-78411	Serial: 8045199 & Up
Mercury/Mariner	200	200	27-78411	Serial: 9157230 & Up
Mercury/Mariner	20	20	27-78411	Also known as MERC 20

Technical Specs

Product Type: Cylinder Block to Baffle Plate Gasket
Application: Mercury/Mariner 20-200 HP Outboard Engines
Installation: Direct replacement
Dimensions: 11.25" H x 6.0" W x 1.13" L
Primary OEM Part Number: 27-78411
Alternative Part Numbers: 27-45088, 18-0373, 31970

What’s in the Box

1x Cylinder Block to Baffle Plate Gasket (Replaces 27-78411)

Installation Notes

Ensure the engine is off, cool, and disconnected from the power source.
Access the cylinder block and baffle plate assembly according to your engine's service manual.
Carefully remove the old gasket, ensuring all remnants and residue are cleaned from the mating surfaces.
Place the new gasket into position, confirming proper alignment with all bolt holes and passages.
Reassemble the components, tightening all fasteners to the manufacturer’s specified torque values.
After reassembly, check for leaks before resuming normal operation.

Troubleshooting & FAQ

How do I know if this gasket fits my specific engine?

Review the Engine & Model Compatibility table and compare the listed models, HP ratings, and especially the serial number ranges to your engine's details. If your engine is not listed or you are unsure, do not purchase without confirming fitment.

What are the signs of a failed baffle plate gasket?

Common symptoms include external oil or water leaks around the cylinder block area, engine overheating, poor performance, or a noticeable loss of compression.

Is any sealant required when installing this gasket?

This gasket is typically designed to be installed dry. However, we strongly recommend consulting your engine’s official service manual for any model-specific instructions regarding the use of sealants.

How often should this gasket be replaced?

This gasket is not a routine maintenance item. It should be replaced if it shows signs of failure (leaks) or during any major engine service or rebuild that requires accessing the baffle plate.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. The part is manufactured in an ISO 9002 facility and batch-inspected for consistency.

Shipping speed & cost?

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

Warranty & returns?

This product is 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 for unused items 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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