Thermostat Cap Gasket – Fits Johnson/Evinrude 6HP (Replaces 311145, 0311145)
Thermostat Cap Gasket – Fits Johnson/Evinrude 6HP (Replaces 311145, 0311145) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Thermostat Cap Gasket – Fits Johnson/Evinrude 6HP (Replaces 311145,...
Product Details
This aftermarket Thermostat Cap Gasket – Fits Johnson/Evinrude 6HP (Replaces 311145, 0311145) ensures a reliable seal for the thermostat housing on Johnson/Evinrude 6HP, 2-Stroke outboard motors manufactured between 1968 and 1979.
It serves as a direct replacement for Evinrude/Johnson part numbers 0311145 and 311145, Sierra 18-0679, and GLM 34000.
- Engineered for an OEM factory fit.
- Seals the gap between the thermostat housing cap and thermostat housing.
- Includes one gasket as pictured.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Evinrude/Johnson | 0311145/311145 | Superseded part number 778235 |
| Sierra | 18-0679 | |
| GLM | 34000 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This part is compatible with the following Johnson/Evinrude models:
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Johnson/Evinrude | 6HP | 6 | 2-Stroke | 1968–1979 | 311145/0311145 | Superseded 778235 |
Technical Specs
- Product Type
- Thermostat Cap Gasket
- Installation
- OEM Factory Fit
- Dimensions
- 5.13" H x 4.0" W x 1.06" L
- Weight
- 0.04 LBS (0.018 kg)
- Other Technical Attributes
- Fits between thermostat housing cap and thermostat housing
What’s in the Box
- 1 x Thermostat Cap Gasket (311145/0311145)
Installation Notes
- Disconnect the engine's battery and allow the engine to cool completely.
- Drain a sufficient amount of coolant to bring the level below the thermostat housing.
- Carefully remove the bolts securing the thermostat housing cap.
- Remove the old gasket and thoroughly clean both mating surfaces, ensuring they are free of old gasket material and debris.
- Position the new gasket correctly onto the thermostat housing.
- Reinstall the thermostat housing cap and tighten the bolts to the manufacturer's specified torque.
- Refill the cooling system with the appropriate coolant.
- Reconnect the battery, start the engine, and carefully check for any leaks around the housing as the engine warms up.
Troubleshooting & FAQ
How do I know if my thermostat gasket is failing?
Common signs of a failed gasket include coolant leaks visible around the thermostat housing, engine overheating issues, or if the old gasket appears cracked, brittle, or compressed upon inspection.
Does this gasket fit my specific 1975 Johnson 6HP motor?
Yes, this gasket is designed to fit all Johnson and Evinrude 6HP 2-stroke models manufactured from 1968 through 1979.
Is any sealant required for installation?
This gasket is typically installed dry. However, it is best practice to consult your engine’s official service manual for any specific recommendations regarding the use of sealing compounds.
What is the purpose of this gasket?
This gasket creates a fluid-tight seal between the thermostat housing and its cap. This prevents coolant from leaking out and ensures the thermostat accurately senses engine temperature.
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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