160° Thermostat Kit – Fits Mercury/Mercruiser 3.7L/4-Cylinder Engines (Replaces 99155T2)
160° Thermostat Kit – Fits Mercury/Mercruiser 3.7L/4-Cylinder Engines (Replaces 99155T2) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
160° Thermostat Kit – Fits Mercury/Mercruiser 3.7L/4-Cylinder Engin...
Product Details
This 160° Thermostat Kit is designed for Mercury/Mercruiser 3.7L (165–190 HP) 4-cylinder engines manufactured between 1983 and 1989. It ensures your engine maintains the correct operating temperature for optimal performance and longevity.
It serves as a direct interchange for Mercury/Quicksilver 99155T2, Sierra 18-3555, and GLM 13420.
- Engineered to maintain a consistent 160°F (71°C) operating temperature.
- Designed for use with aluminum manifolds.
- Includes one thermostat and one mounting gasket for a complete installation.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number |
|---|---|
| Mercury/Quicksilver | 99155T2 |
| Sierra | 18-3555 |
| GLM | 13420 |
Engine & Model Compatibility
Confirm your engine model and year in the table below to ensure accurate fitment.
For Mercruiser Models: Please check your engine's serial number if a specific range is noted.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercruiser | 165 (2 BBL) | 165 | 4-Stroke | 1985–1989 | 99155T2 | Serial Range: 6916779 & Up |
| Mercruiser | 170 (2 BBL) | 170 | 4-Stroke | 1985–1986 | 99155T2 | |
| Mercruiser | 180 (4 BBL) | 180 | 4-Stroke | 1987 | 99155T2 | |
| Mercruiser | 190 (4 BBL) | 190 | 4-Stroke | 1985–1986 | 99155T2 | |
| Mercruiser | 3.7L (2 BBL) | 165 | 4-Stroke | 1988–1989 | 99155T2 | |
| Mercruiser | 3.7LX (4 BBL) | 4-Stroke | 1988–1989 | 99155T2 | ||
| Mercruiser | 470 (2 BBL) | 4-Stroke | 1983–1984 | 99155T2 | Serial Range: 6218037-6916778 | |
| Mercruiser | 485/488 (4 BBL) | 4-Stroke | 1983–1984 | 99155T2 | Serial Range: 6170297-6916778 |
Technical Specs
- Product Type
- Thermostat Kit
- Temperature Rating
- 160°F (71°C)
- Product Dimensions
- 6.0" x 7.5" x 2.0"
- Weight
- 0.28 lb (0.13 kg)
- Installation
- For use with aluminum manifolds
What’s in the Box
- 1 x Thermostat (Replaces Mercury 99155A1)
- 1 x Gasket (Replaces Mercury 27-89656)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery terminals for safety.
- Drain the engine coolant into a suitable container by opening the drain plugs or petcocks.
- Locate the thermostat housing on the engine, typically where the main coolant hose connects.
- Remove the bolts securing the housing cover, and carefully separate it from the manifold.
- Note the orientation of the old thermostat before removing it. Remove the old gasket and clean both mating surfaces thoroughly.
- Place the new thermostat into the housing in the correct orientation. Install the new gasket.
- Re-attach the housing cover and tighten the bolts to the manufacturer's specified torque. Do not overtighten.
- Close the coolant drains and refill the system with the recommended type and amount of coolant.
- Reconnect the battery, start the engine, and check for any leaks around the housing. Allow the engine to reach operating temperature, monitoring the temp gauge.
Troubleshooting & FAQ
How do I know if this thermostat fits my engine?
This kit is specifically for Mercruiser 3.7L 4-cylinder engines from 1983–1989. The most reliable method is to cross-reference your existing part number with those listed in our Part Number Matrix (Mercury 99155T2, Sierra 18-3555, GLM 13420). Always check the compatibility table and any serial number notes for your specific model.
What are the common signs of a failing thermostat?
Symptoms of a faulty thermostat include engine overheating (stuck closed), the engine not reaching normal operating temperature (stuck open), erratic temperature gauge readings, and poor engine performance or fuel economy.
Why is a 160°F rating important for this engine?
The 160°F temperature rating is specified by the manufacturer to ensure the engine operates in its ideal temperature range. Using a thermostat with a different rating can lead to performance issues, increased engine wear, or overheating.
How often should a marine thermostat be replaced?
As a preventative maintenance item, it is recommended to inspect your thermostat annually and replace it every 2-3 years, or immediately if you notice any signs of failure. This is especially critical for boats operated in saltwater due to higher corrosion risk.
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.
Payment & Security
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