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Coolant Temp Sensor 805218T – MerCruiser EFI/MPI
- $55.77
- $55.77
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How to Match This Part
This aftermarket engine coolant temperature sensor replaces Mercury MerCruiser / Quicksilver 805218T (and the earlier number 805218). It is a threaded, two-wire coolant-temperature gauge sender for MerCruiser EFI / MPI sterndrive and inboard engines that need coolant-temperature feedback at the helm gauge or monitoring circuit.
Match this part in this order:
1. OEM or aftermarket number on the removed sensor — 805218T / 805218, Sierra 18-7600, or Mallory 9-42402
2. Engine family and serial — MerCruiser MCM / MIE EFI and MPI applications that call for 805218T in the parts diagram (including verified 4.3L MPI, 350 MAG MPI, 5.0L MPI, and MX 6.2L MPI serial bands below)
3. Physical form — threaded probe-style body with hex flats, molded two-wire plug, and the mating pigtail shown in the product images
Compare thread, probe length, and connector shape with the original part and the product images before ordering. Do not confuse this coolant-temperature sender with MerCruiser intake-air (IAT) sensors such as 805223T — those are separate listings.
Part Number Cross-Reference
Use these verified numbers to confirm you have the correct coolant temperature sensor. Brand names and OEM numbers are for identification only.
| Type | Brand | Part Number | Notes |
|---|---|---|---|
| OEM | Mercury MerCruiser / Quicksilver | 805218T | Primary reference — coolant temperature gauge sender |
| OEM | Mercury MerCruiser | 805218 | Earlier number; functionally replaced by 805218T |
| Aftermarket | Sierra Marine | 18-7600 | Direct cross-reference for MCM / MIE EFI |
| Aftermarket | Mallory Marine | 9-42402 | Direct cross-reference |
This is an aftermarket part manufactured by JLM Marine. It is not sold as a genuine Mercury, MerCruiser, or Quicksilver component.
Compatible Engine Models
Confirm your engine before ordering. Serial location guide: Mercury Parts Diagrams. Always match the OEM number and physical form of the sensor you remove. On verified MerCruiser 4.3L MPI applications, this sensor mounts in the thermostat-housing assembly.
| Brand | Engine Model | Serial Number Range | Notes |
|---|---|---|---|
| MerCruiser | 4.3L MPI Alpha / Bravo | 0M300000–0M614999 | 805218T shown in thermostat-housing diagram |
| MerCruiser | 350 MAG MPI Alpha / Bravo & Horizon Alpha / Bravo | 0M300000–0M599999 | Where-used for 805218 → 805218T |
| MerCruiser | 5.0L MPI Alpha / Bravo | 0M300000–0M599999 | Where-used for 805218 → 805218T |
| MerCruiser | MX 6.2L MPI Bravo & Horizon Bravo | 0M300000–0M599999 | Where-used for 805218 → 805218T |
| MerCruiser | 350 MAG MPI MIE / Horizon MIE | 0M310000–0W389999 (banded) | Confirm serial band on engine ID plate |
| MerCruiser | MX 6.2L MPI MIE / Horizon MIE | 0M310000–0W389999 (banded) | Confirm serial band on engine ID plate |
| MerCruiser | 383 MAG Stroker Inboard | 1G300000 & Up | Where-used for 805218 → 805218T |
Mercury also specifies this sender for MerCruiser EFI sterndrive and inboard applications generally. If your serial range is outside the rows above, order only when the engine parts diagram or the removed sensor shows 805218T / 805218.
Technical Specifications
| Specification | Value |
|---|---|
| Part type | Engine coolant temperature gauge sender / sensor |
| Primary OEM | 805218T (replaces 805218) |
| Electrical connection | 2-wire plug-in with mating pigtail (as shown) |
| Body form | Threaded probe with hex wrench flats |
| Verified MerCruiser mount | Thermostat housing (4.3L MPI diagram) |
| Application class | MerCruiser EFI / MPI sterndrive and inboard (MCM / MIE) |
Package Contents
- 1 × threaded engine coolant temperature sensor
- 1 × two-wire mating connector pigtail, as shown in the product images
Reuse or replace any engine-side sealing compounds or retainers only as specified in the applicable MerCruiser service manual.
Installation Guide
- 1 Allow the engine to cool completely. Disconnect the negative battery cable and relieve cooling-system pressure per the service manual.
- 2 Locate the existing coolant temperature sensor. On verified MerCruiser 4.3L MPI applications it is installed in the thermostat-housing assembly.
- 3 Release the electrical connector without pulling on the wires. If the supplied pigtail is required, splice only with marine-grade sealed connections and preserve original circuit positions.
- 4 Remove the old sensor and compare part number, thread, probe length, and connector shape with the replacement before installation.
- 5 Install the replacement using the tightening method and torque in your MerCruiser service manual. Do not overtighten into aluminum bosses or allow sealant to cover the sensing tip.
- 6 Reconnect wiring and battery, restore coolant as required, inspect for leaks, and verify a plausible temperature reading as the engine warms.
Note: Professional installation is recommended for EFI / MPI coolant-temperature sensors.
Troubleshooting & FAQ
Why Choose JLM MARINE?
- Precision Fit: Cross-referenced to Mercury MerCruiser / Quicksilver 805218T for the MerCruiser EFI / MPI applications listed above.
- Quality Control: Each batch is inspected for dimensional consistency and workmanship.
- Direct from Manufacturer: Aftermarket marine sensors engineered for reliable coolant-temperature feedback on MerCruiser EFI / MPI systems.
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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