160°F Thermostat Kit with Seal & Gasket for Mercury MerCruiser 4-Cylinder Engines (1976–1982; Excludes 470)
160°F Thermostat Kit with Seal & Gasket for Mercury MerCruiser 4-Cylinder Engines (1976–1982; Excludes 470) is backordered and will ship as soon as it is back in stock.
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160°F Thermostat Kit with Seal & Gasket for Mercury MerCruiser ...
160°F Thermostat Kit with Seal & Gasket for Mercury MerCruiser 4-Cylinder Engines (1976–1982; Excludes 470) is backordered and will ship as soon as it is back in stock.
Product Details
This 160°F (71°C) thermostat kit is intended for Mercury MerCruiser-built 4-cylinder stern-drive and inboard/outboard engines from 1976–1982, excluding the MerCruiser 470. It helps the engine maintain its specified operating temperature during normal operation.
The kit includes a 160°F thermostat, one rubber seal ring, and one gasket. It is listed for cross-reference with Mercury/MerCruiser numbers 27-74830, 27-89656-1, 76270T, 99155-1, 99155A1, 99155T1, and 99155T2, plus Sierra 18-3555.
- 160°F (71°C) operating-temperature rating.
- Designed for Mercury MerCruiser-built 4-cylinder engines within the stated application range.
- Includes the thermostat, rubber seal ring, and replacement gasket for the thermostat service.
- Aftermarket replacement component; verify the engine model, year, and existing part number before ordering.
Part Number Matrix
The numbers below are manufacturer and aftermarket references associated with this thermostat application. They are provided for identification and cross-reference purposes; confirm the complete engine application before installation.
| Brand | Reference Number |
|---|---|
| Mercury/MerCruiser | 27-74830 |
| Mercury/MerCruiser | 27-89656-1 |
| Mercury/MerCruiser | 76270T |
| Mercury/MerCruiser | 99155-1 |
| Mercury/MerCruiser | 99155A1 |
| Mercury/MerCruiser | 99155T1 |
| Mercury/MerCruiser | 99155T2 |
| Sierra | 18-3555 |
Engine & Model Compatibility
Company application data identifies this thermostat kit for Mercury MerCruiser-built 4-cylinder engines from 1976–1982, except the MerCruiser 470. The available application data does not establish a complete model-by-model or serial-number chart, so do not rely on horsepower or displacement alone to confirm fitment.
| Engine Brand | Engine Construction | Years | Stroke | Application Notes |
|---|---|---|---|---|
| Mercury MerCruiser | Mercury-built 4-cylinder engines | 1976–1982 | 4-Stroke | Excludes MerCruiser 470; verify the original thermostat and part number. |
Important: This application is not stated for Chevrolet-built 4-cylinder engines or for the MerCruiser 470. Check the engine identification plate, service manual, and thermostat housing before purchase.
Technical Specs
- Product Type
- 160°F thermostat kit
- Temperature Rating
- 160°F (71°C)
- Application
- Mercury MerCruiser-built 4-cylinder engines, 1976–1982, excluding the MerCruiser 470
- Installation Components
- Thermostat, rubber seal ring, and gasket
- Aftermarket Reference
- Sierra 18-3555
What’s in the Box
- 1 x 160°F thermostat, reference Mercury/MerCruiser 99155A1
- 1 x Rubber seal ring
- 1 x Thermostat gasket, reference 27-33918
Installation Notes
- Allow the engine to cool completely before beginning work. Disconnect the battery according to the engine manufacturer's safety procedure.
- Identify the thermostat housing and follow the service manual instructions for draining or containing coolant.
- Remove the housing cover and note the orientation of the original thermostat and seal components.
- Remove the old thermostat, rubber ring, and gasket. Clean the mating surfaces without gouging the housing or manifold.
- Install the replacement thermostat in the same orientation as the original part, then fit the new rubber seal ring and gasket as specified by the service manual.
- Reinstall the housing cover and tighten the fasteners to the manufacturer's specified torque. Do not overtighten.
- Restore the cooling system to the correct level using the recommended coolant and bleeding procedure for the engine.
- Reconnect the battery, start the engine, and inspect the thermostat housing for leaks while monitoring the temperature gauge.
Installation procedures can vary between engine configurations. When the housing arrangement or gasket position differs from the original, stop and consult the applicable Mercury MerCruiser service manual.
Troubleshooting & FAQ
How do I know if this thermostat fits my engine?
Confirm that your engine is a Mercury MerCruiser-built 4-cylinder engine from 1976–1982 and is not a MerCruiser 470 or a Chevrolet-built 4-cylinder engine. Compare the original thermostat and reference number with the compatibility information above before ordering.
What references are associated with this thermostat?
Associated references include Mercury/MerCruiser 27-74830, 27-89656-1, 76270T, 99155-1, 99155A1, 99155T1, and 99155T2, along with Sierra 18-3555. Reference numbers alone do not replace checking the complete engine application.
What does the 160°F rating mean?
The 160°F (71°C) rating is the intended thermostat operating-temperature specification for this application. Use the temperature rating specified for your engine rather than substituting a thermostat based only on physical appearance.
What are common symptoms of a failing thermostat?
A thermostat that is stuck closed may contribute to overheating, while one that is stuck open may prevent the engine from reaching normal operating temperature. Erratic temperature readings or cooling-system leaks can also indicate that inspection is needed.
Does the kit include the gasket and seal?
Yes. The package includes one thermostat, one rubber seal ring, and one gasket identified in the product data as reference 27-33918.
Is this an OEM component?
This listing is for an aftermarket replacement thermostat kit. Mercury and MerCruiser names and reference numbers are used only to identify the intended application and cross-reference numbers.
Safety & Important Information
- Work only on a completely cool engine and follow the applicable marine-engine safety procedures.
- Verify the engine construction, model year, and exclusion for the MerCruiser 470 before ordering.
- Do not rely on a similar-looking thermostat or a single reference number as the only fitment check.
- Professional installation is recommended when the cooling-system configuration or gasket arrangement is unfamiliar.
About Sea Sierra
- Marine Parts Focus — We provide replacement components for marine engines and stern-drive systems.
- Application-Conscious Listings — Product information is organized around engine specifications and reference numbers to support careful fitment checks.
- Practical Service Support — Clear component details help you prepare for routine marine cooling-system maintenance.
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