Mercury MerCruiser Quicksilver Thermostat Housing Gasket 806871
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Mercury MerCruiser Thermostat Housing Gasket 806871
Part Number: 806871 (service format: 27-806871)
Brand: Mercury / Quicksilver
Product Type: Thermostat Housing Gasket (OEM)
System: MerCruiser Engine Cooling
Position: Upper thermostat housing seal (not the lower thermostat housing gasket 530451)
Quantity Required: 1 per thermostat housing assembly
GTIN / UPC: 745061284968
Approximate Dimensions: 2.00 in. x 2.00 in. x 0.20 in.
Approximate Weight: 10 g
Superseded by: 8M0204687, then 8M0238323
What This Part Does
The 806871 is a genuine OEM gasket that seals the thermostat housing on selected MerCruiser gasoline engines, helping control coolant flow and prevent leakage around the thermostat assembly. It is the upper thermostat housing gasket. MerCruiser diagrams commonly show this gasket and the lower thermostat housing gasket (530451) in the same cooling-system assembly — they are separate parts in different positions and are not interchangeable.
Compatible Applications
Fitment depends on engine model, serial number, cooling-system layout, and thermostat housing design. Always confirm by engine serial number before ordering.
- MerCruiser 3.0L GM 181 I/L4 (selected serial ranges)
- MerCruiser 3.0L MPI (selected serial ranges)
- MerCruiser 4.3L V6 (selected serial ranges)
- MerCruiser 4.5L MPI (selected serial ranges)
- MerCruiser 5.0L GM V8 (selected serial ranges)
- MerCruiser 5.7L GM V8 / 350 MAG / 350 MAG MPI / Ski (selected serial ranges)
- MerCruiser 6.2L (selected serial ranges)
- MerCruiser 7.4L / Black Scorpion (selected serial ranges)
- MerCruiser 8.2L / MAG (selected serial ranges)
- Selected Alpha, Bravo, and inboard applications using the newer-style one-piece thermostat housing
Serial Number Notice
Thermostat housing gasket fitment on MerCruiser engines depends on the thermostat housing style, cooling-system layout, and serial number — not engine displacement alone. Confirm by serial number and diagram before ordering. Also note that 806871 has been superseded: if stocking or ordering for a current application, check whether 8M0204687 or 8M0238323 is the current part number in your Mercury catalog.
When to Replace
- Thermostat housing is removed for any reason (replace as standard practice)
- Coolant or raw-water leakage visible around the thermostat housing joint
- Gasket is compressed, torn, hardened, or distorted on inspection
- Thermostat replacement requires disassembly of the housing
- Corrosion or sealing-surface damage is being repaired
Installation Notes
- Clean both thermostat housing mating surfaces and remove all old gasket material before installation — do not gouge the housing sealing surfaces
- While the housing is apart, inspect the thermostat, thermostat sleeve, lower housing gasket (530451), hoses, clamps, and related cooling-system hardware
- Install using correct orientation and follow Mercury service manual torque specifications for the specific engine
- Check for coolant leaks at the housing joint after the engine reaches operating temperature
Related System Components
Parts diagrams commonly show 806871 used with:
- Thermostat 8M0109441 (160°F) — MerCruiser
- Thermostat housing assembly 863457A2
- Thermostat sleeve 806922 / 8M0214947
- Lower thermostat housing gasket 530451 (separate part — not included)
Part Number Cross-Reference
- Original OEM: 806871 / 27-806871
- Also referenced as: 806871Q / 27-806871Q
- Superseded by: 8M0204687 / 27-8M0204687
- Current replacement: 8M0238323 / 27-8M0238323
- Supersession chain: 806871 → 8M0204687 → 8M0238323
Technical FAQ
Q: What is the difference between 806871 and 530451?
A: They are two separate thermostat housing gaskets used in the same cooling-system assembly. The 806871 is the upper thermostat housing gasket; the 530451 is the lower thermostat housing gasket. Both appear in the same MerCruiser thermostat diagram but seal different positions. Ordering one does not include the other.
Q: My parts catalog shows 8M0238323 — is that the same as 806871?
A: Yes. 8M0238323 is the current OEM replacement for 806871, via the intermediate number 8M0204687. The supersession chain is 806871 → 8M0204687 → 8M0238323. All three reference the same thermostat housing gasket application.
Q: How do I know which thermostat housing style my engine uses?
A: Confirm by engine serial number and the thermostat assembly diagram in your MerCruiser service manual or Mercury parts catalog. MerCruiser used different cooling-system layouts across similar-looking engines, so the serial number is the most reliable reference.
Parts Desk Insights
Best use case: Order 806871 (or its current replacement 8M0238323) whenever the thermostat housing is coming off a supported MerCruiser gasoline engine — replacing the housing gasket during any thermostat service is standard practice since access is already there and the part is low cost relative to a repeat coolant leak repair.
Common issues: The most frequent mistake is ordering only one thermostat housing gasket when both the upper (806871 / 8M0238323) and lower (530451) gaskets need replacement during a full housing service. Check the diagram for your engine to confirm how many gaskets are required. A second common issue is not cleaning the housing sealing surfaces adequately before installation — old gasket material left on the mating surface causes the new gasket to leak.
Related Parts
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.