Thermostat Cover Gasket – Fits Mercury/Mariner 2-Stroke Outboards (Replaces 27-14318005)

$3.42

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Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Thermostat Cover Gasket is a direct replacement part designed for various Mercury/Mariner 2-stroke outboards, specifically 20-25 HP models. It ensures a proper seal for the thermostat housing, preventing coolant leaks and maintaining optimal engine temperature.

This part provides a direct interchange for Sierra 18-0323 and Mercury/Quicksilver part numbers 27-14318005, 2714318, 27143182, 27143184, and 27143183.

Installation: Direct replacement
Designed for use with the thermostat cover
Prevents coolant leaks and ensures a secure seal

Part Number Matrix

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

Brand	Part Number
Sierra	18-0323
Mercury/Quicksilver	27-14318005
Mercury/Quicksilver	2714318
Mercury/Quicksilver	27143182
Mercury/Quicksilver	27143184
Mercury/Quicksilver	27143183

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner engines, verify your model and serial number range against this list to ensure a correct fit.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.
Mercury/Mariner	20 (2 CYL.)	20	2-Stroke	0P325500 & Up	27-14318005
Mercury/Mariner	20 JET	20	2-Stroke	0T980000 THRU 0T999999	27-14318005
Mercury/Mariner	20 JET	20	2-Stroke	1B000001 & Up	27-14318005
Mercury/Mariner	25 (2 CYL.)	25	2-Stroke	0P325500 & Up	27-14318005
Mercury/Mariner	25 (2 CYL.)	25	2-Stroke	0T980000 THRU 0T999999	27-14318005
Mercury/Mariner	25 (2 CYL.)	25	2-Stroke	1B000001 & Up	27-14318005

Technical Specs

Product Type: Thermostat Cover Gasket
Installation: Direct replacement
Fuel Type: Gasoline
Dimensions: 5.13 x 4.0 x 1.13 inches
Weight: 0.02 lb (0.009 kg)
Other Technical Attributes: For use with thermostat cover

What’s in the Box

1 x Gasket-Therm Covr (27-14318005)

Installation Notes

Disconnect the negative battery cable before beginning work.
Allow the engine to cool completely and drain the engine coolant into a suitable container.
Locate the thermostat housing on the engine and remove the mounting bolts.
Carefully remove the thermostat cover. You may need to gently tap it to break the seal.
Remove the old gasket and thermostat. Thoroughly clean any old gasket material or sealant from both the housing and cover surfaces.
Install the new thermostat and gasket, ensuring they are correctly oriented.
Reinstall the thermostat cover and tighten the bolts to the manufacturer's specified torque in a crossing pattern.
Refill the cooling system with the appropriate coolant.
Reconnect the battery, start the engine, and check carefully for any signs of leaks around the housing.

Troubleshooting & FAQ

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

This gasket is for specific Mercury/Mariner 20-25 HP 2-stroke outboards. To ensure a correct fit, please check the compatibility table using your engine's model and serial number range. Comparing the part to your old one visually is also a good practice.

What are the signs of a failing thermostat cover gasket?

Common signs include coolant leaks around the thermostat housing (especially when the engine is warm), engine overheating or running at an improper temperature, and visible cracks, brittleness, or deterioration of the old gasket upon inspection.

When should this gasket be replaced?

It is best practice to replace the thermostat cover gasket any time you service the thermostat or the cooling system. Gaskets are single-use components designed to compress and create a seal, and they may not reseal properly if reused.

Why is my engine overheating after replacing the gasket?

If overheating occurs after replacement, ensure the thermostat was installed correctly (not upside down), that no air is trapped in the cooling system (it may need to be "burped"), and that the housing bolts are torqued to spec. Also, verify that the new gasket has created a complete seal with no leaks.

Is this an OEM or aftermarket part?

This listing is for an aftermarket replacement part, not an OEM component. It has been engineered to meet or exceed OEM-level specifications using comparable materials. Our parts are manufactured in an ISO 9002 certified facility and are batch-inspected to ensure quality and consistency.

What are the shipping speed and cost?

We ship worldwide quickly, with typical transit times of 5–15 days for most regions. Standard shipping is free on all orders. Expedited shipping options, where available, will be presented at checkout for an additional cost.

What is the warranty and return policy?

This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter an issue, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. Please see our full policy page or reach out for instructions.

Safety & Important Info

Verify images and specifications against 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 rigorously tested for real-world conditions.
Fast Global Fulfillment — We offer free standard delivery to most regions with an average transit time of 5–15 days.
Manufacturer-Direct Value — By working directly with manufacturers, we provide fair pricing without compromising on materials or quality control.

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