Gasket - Thermostat Housing – Fits Mercury/Mercruiser 470 (Replaces 27-74830)
Gasket - Thermostat Housing – Fits Mercury/Mercruiser 470 (Replaces 27-74830) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Gasket - Thermostat Housing – Fits Mercury/Mercruiser 470 (Replaces...
Product Details
This replacement Thermostat Housing Gasket is engineered for Mercury Mercruiser 470 series 4-stroke engines manufactured between 1976 and 1982. It creates a secure, reliable seal between the thermostat housing and the reservoir assembly to prevent coolant leaks and ensure optimal engine cooling performance.
This part is a direct cross-reference for Mercury part number 27-74830 and Sierra aftermarket part 18-2843.
- Installs between the thermostat housing and the coolant reservoir.
- Made from durable composite gasket material to withstand high temperatures and harsh marine environments.
- Precision-cut to OEM specifications for a direct fit and proper seal.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 27-74830 |
| Sierra | 18-2843 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercruiser models, verify your engine's serial number falls within the specified range for an exact match.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercruiser | 470 MCM | 170 | 4-Stroke | 1976–1979 | 27-74830 | Serial Range: 4208730-5520114 |
| Mercruiser | 470 MCM | 170 | 4-Stroke | 1980–1982 | 27-74830 | Serial Range: 5520115-6218036 |
| Mercruiser | 470 MIE | 170 | 4-Stroke | 1980–1981 | 27-74830 | Serial Range: 5520115-6218036 |
Technical Specs
- Product Type
- Thermostat Housing Gasket
- Installation Location
- Between thermostat housing and reservoir
- Material
- Composite gasket material
- Dimensions
- 7.5 x 6.0 x 1.13 inches
- Weight
- 5 ounces (0.14 kg)
- Operating Temperature
- Designed for marine cooling system temperatures
- Function
- Seals thermostat housing to reservoir connection
What’s in the Box
- 1 x Gasket, Thermostat Housing to Reservoir (Replaces 27-74830)
Installation Notes
- Ensure the engine is cool and disconnect the battery. Drain the engine coolant into a suitable container to a level below the thermostat housing.
- Disconnect any hoses attached to the thermostat housing, noting their orientation for reassembly.
- Carefully unbolt and remove the thermostat housing assembly.
- Remove the old gasket and thoroughly clean both mating surfaces. Ensure they are completely free of old gasket material, sealant, corrosion, and debris.
- Position the new gasket correctly on the cleaned surface. Do not use sealant unless specifically required by the engine's service manual.
- Reinstall the thermostat housing and tighten the bolts to the manufacturer's recommended torque specification, typically in a crisscross pattern to ensure even pressure.
- Reconnect all hoses securely to their original positions.
- Refill the cooling system with the correct type and amount of coolant.
- Reconnect the battery, start the engine, and let it reach operating temperature while carefully checking for any leaks around the housing.
Troubleshooting & FAQ
What are the signs of a failing thermostat housing gasket?
Common signs include visible coolant leaks or drips around the thermostat housing area, engine overheating, and frequent low coolant level warnings. You may also notice dried coolant residue (typically white, green, or pink) on the engine block near the housing.
Is a sealant required when installing this gasket?
This gasket is designed to create a seal on its own between clean, flat surfaces. Generally, sealants are not required or recommended, as excess sealant can break off and enter the cooling system, potentially causing blockages. Always consult your engine's service manual for specific instructions.
How can I confirm this gasket fits my specific Mercruiser 470 engine?
Check your engine's model and, more importantly, its serial number. The compatible serial number ranges for each model year are listed in the "Engine & Model Compatibility" table on this page. If your serial number falls within one of those ranges, the part will fit.
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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