Thermostat Gasket – Fits Mercury/Mercruiser 3.7L 224 CID L4 (Replaces 27-89656-1)
Thermostat Gasket – Fits Mercury/Mercruiser 3.7L 224 CID L4 (Replaces 27-89656-1) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat Gasket – Fits Mercury/Mercruiser 3.7L 224 CID L4 (Replac...
Product Details
This replacement Thermostat Gasket is designed for Mercury/Mercruiser 3.7L (224 CID) 4-cylinder engines, including models with ratings from 165 HP to 190 HP, manufactured between 1976 and 1989. It provides a reliable seal between the thermostat housing and the engine block, preventing coolant leaks.
It serves as a direct interchange for Mercury part numbers 27-89656-1, 27-896561, 76270T, and 99155T2, as well as GLM 32100 and Sierra 18-2555.
- Installs directly between the thermostat housing and engine block.
- Engineered from high-quality composite gasket material for durability.
- Ensures a precise fit for specified marine 4-cylinder engines.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By | Notes |
|---|---|---|---|
| Mercury | 27-74830 | 27-89656-1 | |
| Mercury | 27-89656-1 | 99155T2 | |
| Mercury | 27-896561 | 99155T2 | |
| Mercury | 76270T | ||
| Mercury | 99155T2 | Current OEM part number. | |
| GLM | 32100 | Aftermarket Cross-Reference | |
| Sierra | 18-2555 | Aftermarket Cross-Reference | |
| OMC | 0508570 | Cross-reference only | |
| OMC | 0508576 | Cross-reference only | |
| OMC | 0508621 | Cross-reference only | |
| OMC | 0508623 | Cross-reference only |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercruiser models, this gasket is compatible with the 3.7L (224 CID) 4-cylinder series manufactured between 1976 and 1989.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercruiser | MCM 470 | 190 | 4-Stroke | 1976–1982 | 27-89656-1 | Supersedes 27-74830 |
| Mercruiser | 470 | 190 | 4-Stroke | 1983–1984 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 485 | 185 | 4-Stroke | 1980–1982 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 488 | 185 | 4-Stroke | 1983–1984 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 170 | 170 | 4-Stroke | 1985–1986 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 190 (4 cyl) | 190 | 4-Stroke | 1985–1986 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 165 (4 cyl) | 165 | 4-Stroke | 1987 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 180 | 180 | 4-Stroke | 1987 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 3.7L | 165 | 4-Stroke | 1988–1989 | 27-89656-1 | Used with thermostat cover 89659A3 |
| Mercruiser | 3.7LX | 180 | 4-Stroke | 1988–1989 | 27-89656-1 | Used with thermostat cover 89659A3 |
Technical Specs
- Product Type
- Thermostat Gasket
- Application
- Marine 4-cylinder engines
- Installation Location
- Between thermostat housing and engine block
- Material
- Composite Gasket Material
- Dimensions
- 1.06″ L x 7.5″ W x 6.0″ H
- Weight
- 0.16 oz (4.5 g)
- OEM Supersession
- 27-74830 → 27-89656-1/27-896561 → 99155T2
What’s in the Box
- 1 x Thermostat Gasket (Replaces 27-89656-1)
Installation Notes
- Disconnect the boat's battery and drain the engine coolant to a level below the thermostat housing.
- Locate and unbolt the thermostat housing cover from the engine block.
- Carefully remove the old thermostat and gasket. Thoroughly clean both mating surfaces to remove any old gasket material or sealant residue.
- Position the new thermostat gasket correctly onto the engine block, aligning it with the bolt holes.
- Install the thermostat, ensuring it is oriented correctly according to your service manual.
- Re-install the housing cover and tighten the bolts to the manufacturer's recommended torque specification in a star or crisscross pattern.
- Refill the cooling system with the appropriate coolant, reconnect the battery, and start the engine to check for any leaks around the housing.
Troubleshooting & FAQ
How do I know if my thermostat gasket is failing?
Common signs of a failed thermostat gasket include coolant leaks visible around the thermostat housing, engine overheating, or erratic temperature gauge readings. A visual inspection may reveal coolant stains or drips in the area.
Can I use sealant with this gasket?
This composite gasket is designed to create a seal when installed dry. Applying additional sealants is generally not recommended as it can interfere with the seal, unless explicitly required by your engine’s service manual.
Should I replace my thermostat at the same time?
Yes, it is highly recommended to replace the thermostat whenever you replace the gasket. This ensures both components are new and function correctly together, preventing potential cooling system issues and saving you from performing the same repair twice.
What is an OEM vs. Aftermarket part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials, designed to offer the same performance and fit. Our parts are manufactured in an ISO 9002 facility and are batch-inspected for quality and consistency.
How much is shipping and how fast is it?
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free to most locations. Expedited shipping options and exact costs will be displayed at checkout if available for your region.
What is the warranty and return policy?
This part is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for unused parts in their original condition. Please see our policy page or contact us for instructions.
Safety & Important Info
- Verify images and specifications against your original part before purchasing. If anything differs—even if your model appears on a compatibility list—do not purchase.
- This is an aftermarket replacement component, not an original equipment manufacturer (OEM) part.
- Professional installation is recommended for safety and optimal performance. Improper installation can lead to engine damage.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and rigorously tested for real-world reliability.
- 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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