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Water Temp Sender 806490T – MerCruiser Sterndrive/Inboard
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How to Match This Part
This aftermarket engine water temperature gauge sender replaces Mercury / MerCruiser 806490T. It threads into a coolant passage (thermostat housing, intake manifold, or cylinder head) and sends the temperature signal to your dash gauge. It is a dual-station sender with a single 10-32 stud terminal, so one unit can drive two US ohm-scale temperature gauges when the wiring supports dual-station use.
Match this part in this order:
1. OEM number on the removed sender (stamped or printed on the hex body)
2. Thread size of the sender port — this unit is 3/8"-18 NPT; some engines use 1/2"-14 NPT instead
3. Engine identification on MerCruiser sterndrive / inboard: model and serial on the engine block or flame arrestor cover plate
Identify the form: hex body, tapered male pipe thread, sensing probe into the coolant, and one top stud terminal (gauge wire under the stud nut — no pigtail harness).
Part Number Cross-Reference
Use this table to confirm equivalent OEM and aftermarket numbers for the same sender style. Numbers written with or without leading zeros refer to the same catalog item when listed under one brand.
| Type | Brand | Part Number | Notes |
|---|---|---|---|
| OEM | Mercury / MerCruiser | 806490T | Primary original equipment number |
| OEM | Mercury / MerCruiser | 97257A1 | Superseded / prior catalog number, same sender |
| OEM | Volvo Penta | 3853787 | Equivalent temperature sender number |
| OEM | OMC Cobra | 980613 | Equivalent temperature sender number |
| Aftermarket | Sierra | 18-5897 | Direct replacement, dual station |
| Aftermarket | Mallory | 9-42400 | Direct replacement |
| Aftermarket | OBR | MR-583 | Direct replacement |
Compatible Engine Models
Confirm your application by OEM number and thread size before ordering. On MerCruiser sterndrive and inboard engines, the model and serial identification is on the engine block or the flame arrestor cover plate. You can also cross-check parts breakdowns in the Mercury Parts Diagrams. Important: some engines were built with a 1/2"-14 NPT sender port instead of 3/8"-18 NPT — always compare the thread on the sender you remove.
| Brand / Drive Type | Application | Notes |
|---|---|---|
| MerCruiser sterndrive (MCM) and inboard (MIE) | Engines calling for sender 806490T | Confirm 3/8"-18 NPT port and gauge wiring |
| Volvo Penta sterndrive / inboard | Applications using sender 3853787 | Confirm by number on the removed sender |
| OMC Cobra sterndrive | Applications using sender 980613 | Confirm by number on the removed sender |
Technical Specifications
| Specification | Value |
|---|---|
| Primary OEM | 806490T |
| Product type | Engine water temperature gauge sender |
| Thread size | 3/8 in. – 18 NPT |
| Terminal | 10-32 threaded stud (single terminal) |
| Gauge stations | Dual station |
| Gauge scale compatibility | US ohm-scale marine temperature gauges |
| Application | MerCruiser MCM/MIE coolant temperature signal to dash gauge |
Installation Guide
Allow the engine to cool fully. Disconnect the battery negative cable and relieve cooling-system pressure per the service manual before opening the sender port.
Label and remove the gauge wire from the old sender stud. Unscrew the old sender and compare its thread to this 3/8"-18 NPT unit. Do not force a mismatched thread.
Apply a thin coat of marine-grade thread sealant suitable for NPT fittings (avoid sealant on the electrical stud). Thread the new sender in by hand, then tighten snugly with the correct wrench — do not over-torque the body.
Reconnect the gauge wire under the 10-32 stud nut with the insulating washer seated correctly. Refill / burp the cooling system, reconnect the battery, start the engine, and check for coolant leaks and a stable gauge reading as the engine warms.
If you are unsure about dual-station wiring or gauge calibration, have a marine technician complete the install.
Troubleshooting & FAQ
Important Notes
- Verify OEM 806490T (or the listed equivalents) and 3/8"-18 NPT thread against the removed sender before purchase.
- This is an aftermarket replacement and is not a genuine Mercury / MerCruiser component.
- Professional installation and a post-install leak / gauge check are recommended.
Why Choose JLM MARINE?
- Precision Fit: Thread and terminal layout matched to MerCruiser 806490T dual-station sender applications.
- Quality Control: Each batch is inspected for dimensional consistency and workmanship.
- Direct from Manufacturer: Aftermarket marine parts engineered for reliable gauge-sender service.
We can ship to virtually any address in the world with free shipping available for most regions.
For our typical US and Canadian customers , our shipping timeframes are as follows:
- Amazon FBA: orders will be delivered within 1-5 business days after placing the order (during certain special periods such as major promotions, Christmas, etc., the delivery time of Amazon FBA may be affected).
- US warehouse shipment: orders will be delivered within 5 days after placing the order.
- China warehouse shipment: orders will be delivered about 12 days after placing the order.
When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.
Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.
Founded in 2002, JLM Marine has established itself as a dedicated manufacturer of high-quality marine parts, based in China. Our commitment to excellence in manufacturing has earned us the trust of top marine brands globally.
As a direct supplier, we bypass intermediaries, which allows us to offer competitive prices without compromising on quality. This approach not only supports cost-efficiency but also ensures that our customers receive the best value directly from the source.
We are excited to expand our reach through retail channels, bringing our expertise and commitment to quality directly to boat owners and enthusiasts worldwide.
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