Indmar LY6 Thermostat 160°F Drilled – 986115D
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
The Indmar Thermostat 986115D is a genuine OEM 160°F drilled thermostat designed for GM Gen IV LY6 and L96 marine engines equipped with closed cooling systems. This thermostat features a precision 5/32” bypass (drilled) hole, allowing controlled coolant flow during warm-up to reduce thermal shock and improve temperature stability.
Engineered specifically for Indmar applications, this thermostat ensures consistent operating temperature, optimized combustion efficiency, and proper coolant circulation through the heat exchanger system.
Key Features
- Genuine Indmar OEM thermostat
- 160°F operating temperature
- Integrated drilled bypass (5/32”) for improved coolant flow
- Designed for closed cooling (freshwater cooled) systems
- Maintains stable engine temperature under load
- Direct replacement — no modification required
Engine Compatibility
Fits Indmar GM Gen IV closed cooled engines:
- LY6 6.0L V8
- L96 6.0L V8
Applications include:
- MasterCraft, Malibu, Supra, Moomba, and other Indmar-powered inboards
- Closed cooling / heat exchanger equipped engines
✔ Specifically for closed cooling systems
✔ Not for raw water cooled thermostat housings
Serial Number Fitment Notice
Fitment varies by engine configuration and model year. Always confirm using your engine serial number or engine model (LY6/L96) before ordering.
When This Part Needs Replacement
- Engine running too hot or overheating
- Engine not reaching or holding temperature
- Temperature fluctuations under load
- Thermostat sticking or corrosion present
- Cooling system service interval
Installation Notes
- Install with spring side toward engine
- Ensure drilled bypass hole is oriented correctly (typically upward)
- Replace gasket/seal during installation (sold separately)
- Inspect heat exchanger and coolant passages
- Verify coolant condition before reassembly
Alternate / Superseded / Cross-Reference Part Numbers
- Indmar: 986115D
- Related (non-drilled variant): 986115
- Comparable applications: GM Gen IV 6.0L marine thermostats
Parts Desk Insight
The drilled bypass is the key difference on this thermostat. It allows a small amount of coolant to circulate before the thermostat fully opens, which helps prevent hot spots and improves temperature stability — especially important on closed cooling Indmar setups. Installing a non-drilled thermostat in these engines can lead to erratic temperature behavior.
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 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.