Mercury MerCruiser Transmission Temperature Switch Assembly 88031 | OEM 87-88031
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Mercury MerCruiser Transmission Temperature Switch Assembly 88031
Part Number: 88031 | 87-88031
Supersedes: 813708 | 87-813708
Brand: Mercury Marine / MerCruiser / Quicksilver
Product Type: Transmission oil temperature switch assembly — OEM
System: Marine transmission / propulsion electrical
GTIN / UPC: 745061202955
The Mercury MerCruiser 88031 / 87-88031 is a genuine OEM transmission oil temperature switch assembly used in selected MerCruiser inboard and diesel propulsion packages. It installs directly in the marine transmission and monitors transmission oil temperature for the warning or monitoring circuit. Part 88031 is the current OEM replacement for the earlier 813708 / 87-813708.
Compatible Applications
Shown in multiple MerCruiser marine transmission diagrams — confirm part 88031 / 87-88031 in your transmission diagram before ordering:
- Velvet Drive 71C
- Velvet Drive 72C
- Hurth transmission installations
- 45C
- 45C DTS
- 45IV
- Selected MerCruiser MIE gasoline and diesel propulsion packages
Legacy engine applications covered via supersession from 813708 include selected:
- 5.7L MIE / GM 350 V8
- 7.4L MIE / GM 454 V8 & 7.4L MPI MIE
- 8.2L MIE / GM 502 V8 & 8.2L MPI MIE
- 350 MAG MPI MIE | 454 MAG MPI Horizon
- MerCruiser VM 3.0L / 183 CID diesel
- MerCruiser VM 3.6L / 219 CID diesel
- D254 Turbo AC
- 7.3L diesel applications where the original diagram specifies 813708 or 88031
Serial Number & Diagram Fitment Notice
Fitment is determined by transmission model and propulsion package, not engine displacement alone. Always confirm part 88031 / 87-88031 in the transmission-specific Mercury parts diagram for your serial number range before ordering. If you are unsure, provide your MerCruiser engine and transmission serial numbers for fitment assistance.
When to Replace
- A transmission over-temperature warning is occurring without confirmed overheating
- The warning circuit fails to respond during diagnostic testing
- Switch has damaged or corroded electrical terminals
- Oil leakage is present at the switch installation point
- Switch fails continuity or temperature testing per the service manual
- Transmission electrical or warning-system diagnosis identifies the switch as faulty
A transmission temperature warning does not automatically indicate a failed switch. Verify transmission oil level, oil condition, cooler flow, and actual operating temperature before replacing electrical components.
Installation Notes
- Disconnect battery power before electrical service
- Identify the correct temperature-switch position in the transmission parts diagram
- Inspect the electrical terminal and harness connector for corrosion before installation
- Check the surrounding transmission oil system for leakage during the same service
- Do not substitute an engine coolant temperature switch — this is a transmission-specific component
- Follow the applicable Mercury service manual for switch testing, sealing, and tightening specifications
Superseded & Alternate Part Numbers
- 88031 — Current Mercury / MerCruiser part number
- 87-88031 — Full Mercury catalog number
- 813708 — Earlier temperature switch (superseded by 88031)
- 87-813708 — Earlier full Mercury catalog number
Mercury lists 88031 as the current functional replacement for 813708. The replacement may differ visually from the original switch.
Related Transmission Components
- Mercury MerCruiser Trim / Trailer Switch Assembly 18286T34
- Mercury MerCruiser Quicksilver Switch Assembly 54211T
- Mercury MerCruiser Harness Repair Kit 8M0062017
Technical FAQ
Q: How do I know if 88031 fits my transmission?
Locate part 88031 / 87-88031 in the Mercury diagram for your specific transmission model (71C, 72C, Hurth, 45C, 45IV, etc.) and propulsion serial number. The transmission diagram is the correct reference — not the engine diagram.
Q: What replaced 813708?
Mercury lists 88031 / 87-88031 as the current replacement for 813708 / 87-813708. The two part numbers are functionally equivalent for the covered applications, though the replacement may differ in appearance.
Q: The over-temperature warning came on — does that mean this switch is bad?
Not necessarily. Check transmission oil level, oil condition, and cooler flow first. A genuine overtemperature condition will trigger the same warning as a failed switch. Diagnose the root cause before replacing electrical components.
Parts Desk Insights
The critical detail with 88031 is its location: this is a marine transmission temperature switch, not a general engine temperature sender. Mercury uses this switch across several transmission families — Velvet Drive 71C/72C, Hurth, and 45-series — so the transmission diagram is the correct fitment reference, not the engine model alone. The most common ordering mistake is pulling the engine part number rather than the transmission diagram part number, which can result in ordering the wrong sensor entirely. When diagnosing a transmission over-temperature warning, always rule out actual overheating (oil level, cooler flow, operating conditions) before condemning the switch.
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.