Mercury MerCruiser Quicksilver 160°F Thermostat 76270T

160°F Engine Thermostat — OEM Reference 76270T

Part Number: 76270T
Brand: Mercury Marine / MerCruiser / Quicksilver
Official Product Type: Engine Thermostat — 160°F
Supersedes: 76270 (earlier reference, same application)
Replaced By: 76270T is the current active OEM part number
Engine Family: MerCruiser 3.7L / 224 cu. in. Inline-Four (Mercury 224)
System: Engine Cooling — Thermostat Housing / Coolant Flow Control
Diagram Position: Thermostat housing between the exhaust-manifold cooling passage and coolant reservoir
GTIN: 745061177307

What This Thermostat Does

This genuine Mercury Marine OEM thermostat regulates coolant flow on early MerCruiser 3.7L inline-four engines, opening at 160°F to allow coolant circulation once the engine reaches operating temperature. It is the correct thermostat for the 470 and 485 platforms within the documented serial number range — not a universal marine thermostat, and not interchangeable with the 807252-series thermostat kits used on later GM V6 and V8 MerCruiser engines. These engines use a Mercury-built inline-four cooling system with a distinctive housing and hose layout, so matching by OEM part number and serial number is essential.

Compatible Applications

Fitment is serial-number specific on 3.7L engines. Confirm the complete engine model and serial number before ordering.

• MerCruiser 470 (2 BBL.) — 1976–1979, serial range 4208730–6218036
• MerCruiser 470 (2 BBL.) — 1980–1982, serial range 5520115–6218036
• MerCruiser 470 MIE — 1980–1981, serial range 5520115–6218036
• MerCruiser 485 (2 BBL.) — 1980–1982, serial range 5685394–6218036

Confirmed serial cutoff: 470 / 485 models with serial number 6218036 and below.

Serial Number Fitment Notice

Fitment on early MerCruiser 3.7L engines is serial-number specific. Later 470 / 485 serial numbers may use a different thermostat. Always confirm the engine model and full serial number before ordering.

When to Replace This Thermostat

Replace when diagnosis points to any of the following:

• Engine running consistently too cold
• Engine overheating or slow warm-up
• Unstable or inconsistent operating temperature
• Thermostat stuck open or closed
• Corrosion or mechanical damage found during cooling-system service

Service Interval

Inspect at every cooling-system service. Replace whenever the thermostat housing is opened, if the thermostat fails a bench test, or if temperature symptoms are present. On older 3.7L engines, inspect the cooling passages and housing for corrosion at the same time.

Dimensions

Weight: approx. 0.15 kg (0.33 lb) | Temperature rating: 160°F | Quantity per assembly: 1

Installation Notes

• Install with the spring side facing the engine block.
• Replace the thermostat housing gaskets during installation — sold separately.
• Mercury diagrams show this thermostat installed with:
  • Mercury MerCruiser Quicksilver Exhaust Manifold End Cap Gasket 480431 — thermostat housing to exhaust manifold
  • Thermostat housing to coolant reservoir gasket 74830 (verify availability separately)
• Clean the thermostat housing and mating surfaces thoroughly before reassembly.
• Inspect water passages for corrosion or scale — common on older 3.7L engines.
• Tighten housing fasteners to the torque specification in the applicable MerCruiser service manual.
• Verify proper coolant circulation after startup.

Kit Contents

Thermostat only. Gaskets and seals are sold separately — order 480431 and 74830 from your parts diagram to complete the installation.

Alternate and Superseded Part Numbers

• Current: 76270T
• Supersedes: 76270
• Aftermarket cross-reference: Sierra 18-3552, GLM 13050, Mallory 9-43000

Related Parts

• Mercury MerCruiser Quicksilver Exhaust Manifold End Cap Gasket 480431 — thermostat housing to exhaust manifold gasket
• Thermostat housing to coolant reservoir gasket 74830 — verify by diagram
• MerCruiser 3.7L thermostat housing — inspect for corrosion when replacing thermostat
• Coolant hoses — inspect and replace if hardened or cracked during service

Parts Desk Insights

The most common issue with this thermostat is customers ordering a generic 160°F marine thermostat and finding it doesn’t fit. The MerCruiser 470 and 485 use a Mercury-built inline-four cooling system with a unique housing layout — thermostat fit depends on the housing opening, not just the temperature rating. When replacing 76270T, it’s worth opening the housing fully to inspect the cooling passages for corrosion or scale, which is common on 3.7L engines of this vintage. Order both housing gaskets (480431 and 74830) at the same time so the job doesn’t stall waiting for parts.

Technical FAQ

Q: Is this the same as a 807252-series thermostat kit?
No. The 807252-series is for later GM V6 and V8 MerCruiser engines. 76270T is specific to the Mercury-built 3.7L / 224 inline-four (470 / 485) and is not interchangeable.

Q: What is the difference between 76270 and 76270T?
76270T is the current OEM version and supersedes the earlier 76270. They are the same thermostat for the same application — 76270T is the part to order today.

Q: Do I need to replace the gaskets when I replace the thermostat?
Yes. The thermostat housing uses two gaskets — 480431 (housing to exhaust manifold) and 74830 (housing to coolant reservoir). Both should be replaced any time the housing is opened.

Q: How do I know if my thermostat has failed?
Common signs include the engine running too cold, overheating, slow warm-up, or unstable temperature. A bench test (heat in water and observe opening) can confirm failure before ordering a replacement.