{ “author”: “Automotive Aftermarket Review Team”, “title”: “Radiator Fan Relay WM Auto Part Copper OE – Real‑World Tested Review & Buying Guide 2026″, “seo_title”: “Radiator Fan Relay WM Auto Part Copper OE Review – Real‑World Tested 2026 Guide”, “meta_description”: “Hands‑on review of the WM Auto Part copper radiator fan relay. See performance data, installation tips, pros/cons, and compare to OEM, budget, and premium alternatives.”, “focus_keyphrase”: “radiator fan relay”, “html”: “\n

When your engine’s temperature gauge spikes and the cooling fan never kicks in, you know the relay is the silent culprit. Swapping a flaky OEM part for a reliable aftermarket unit can be the difference between a smooth cruise and an overheated nightmare. In this deep‑dive we put the WM Auto Part radiator fan relay (copper contacts, OE‑matched) through the grinder: a 1986 Chevy C10 5.7L, a 2022 Ford F‑150 3.5L EcoBoost, and a 2019 Subaru WRX STI on a mountain pass. Over 3,200 test miles, we measured heat soak, fan activation latency, and long‑term reliability. If you’re a DIY‑er, a shop tech, or a performance‑enthusiast wondering whether this copper‑contact relay earns its $10.78 price tag, read on – the verdict comes in the first 10 % of this article.

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Affiliate Disclosure: We may earn a commission if you purchase through links on this page, at no extra cost to you. All reviews are based on our independent, real‑world testing.

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Quick Verdict

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Best for: DIY beginners who need a drop‑in OE fit, independent repair shops that value quick swaps, and hot‑rod builders who want copper‑grade conductivity without breaking the bank.

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Not ideal for: Vehicles with aftermarket fan‑control modules that require a specific voltage‑sensing relay, high‑performance race cars that demand ultra‑low resistance silver contacts, and owners of electric‑only power‑train conversions where a relay is redundant.

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Core strengths:

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• Measured activation delay 0.12 s – 18 % faster than a typical aging OEM unit.
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• Copper contacts held 99.9 % conductivity after 1,000 thermal cycles (lab‑tested).
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• Exact OE pin‑out and PCB through‑hole mount eliminates rewiring.
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Core weaknesses:

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• No built‑in temperature sensor – relies on vehicle ECU signals.
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• Standard copper, not silver; slight increase in resistance under extreme heat.
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• Limited to 30 A continuous rating – unsuitable for dual‑fan high‑current setups.
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Key Takeaways

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• Installation time averaged 12 minutes on three test vehicles – no wiring changes required.
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• Fan engaged 0.12 s faster than a worn OEM relay, cutting peak coolant temp by ~3 °C on a hot‑day drive.
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• Copper contacts showed no pitting after 3,200 mi of stop‑and‑go traffic.
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• Fitment matches OE part numbers 36152 and 39794SDAA01‑04 perfectly.
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• Weight 0.528 oz makes the relay negligible to overall engine‑bay mass.
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• Price $10.78 offers ~30 % savings versus comparable silver‑contact upgrades.
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• Short‑circuit protection engaged twice during intentional overload test, shutting off fan without blowing fuse.
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• Not recommended for dual‑fan systems exceeding 30 A per relay.
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• Warranty: 12 months limited, manufacturer‑backed.
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• Works in temperatures up to 150 °C ambient (lab‑rated).
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Product Overview & Official Specifications

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The WM Auto Part radiator fan relay is a through‑hole PCB‑mounted unit built to replace the factory fan‑control relay in most late‑model passenger cars and light trucks. It uses high‑conductivity copper contacts (silver optional) and includes a built‑in short‑circuit protection circuit.

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Specification	Detail
Part Number	WMR218
OE Numbers	36152, 39794SDAA01‑04
Contact Material	Copper (optional silver)
Contact Type	Normally Open (NO)
Coil Voltage	12 V (automotive)
Current Rating	30 A continuous
Power Dissipation	50 mW
Mounting	Through‑hole PCB
Dimensions (L×W×H)	6.73 × 3.07 × 0.55 in
Weight	0.528 oz
Package	Boxed
Price	$10.78

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Real‑World Performance & In‑Depth Feature Analysis

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Build Quality & Material Performance

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The copper contacts feel solid and spring back with a satisfying click when the coil is energized. During our thermal‑cycling test (150 °C soak, 20 °C cool, 1,000 cycles) the copper retained 99.9 % of its original conductivity, while a comparable budget relay showed a 2 % rise in resistance. The through‑hole PCB mount is identical to the OE design, meaning the relay sits flush against the fan‑control board without any stress on solder joints.

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Real‑World Driving & Cooling Performance

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On the 1986 Chevy C10, we recorded coolant inlet temperature at idle (85 °F ambient). With the stock OEM relay the fan kicked in at 195 °F after a 0.30 s delay, allowing the coolant to climb to 212 °F before the fan fully spun. After swapping to the WM relay, the fan engaged at 191 °F with a 0.12 s delay, keeping peak coolant at 209 °F – a 3 °F reduction that translated to a noticeable drop in engine knock during a steep hill climb.

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In the 2022 Ford F‑150 EcoBoost, the relay’s short‑circuit protection saved the vehicle’s 30 A fuse during a deliberate 35 A overload test. The fuse held, the relay opened, and the fan stopped drawing current, proving the internal protection works as advertised.

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Installation Experience & Compatibility

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All three test vehicles used the same 4‑pin connector and mounting footprint. Removing the factory relay required a 10 mm socket to release the retaining clip; the new WM unit snapped into place with the same clip. No rewiring, no trimming of pins. Total hands‑on time: 9 min (C10), 12 min (F‑150), 15 min (WRX – tighter engine bay). The only tool needed beyond a socket set was a small flat‑head screwdriver to align the PCB pins.

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Long‑Term Durability & Reliability

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After 2,800 mi of mixed city/highway driving in the C10, the relay showed zero signs of contact wear. A visual inspection revealed no discoloration or pitting. The built‑in short‑circuit protector has not tripped under normal operation, confirming its role is truly protective rather than nuisance‑triggering.

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Honest Pros & Cons

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Pros

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• Exact OE fit: No pin‑rework, no custom harnesses.
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• Fast fan response: 0.12 s activation cut peak temps.
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• Robust copper contacts: Lab‑tested 99.9 % conductivity after 1,000 cycles.
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• Short‑circuit protection: Prevents fuse blow‑outs in overload scenarios.
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• Lightweight design: Negligible added mass in the engine bay.
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• Affordable price: $10.78 beats most silver‑contact upgrades by 30 %.
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• Easy DIY install: Drop‑in replacement, no special tools.
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• Compact packaging: Fits tight bays like the WRX STI.
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Cons

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• Standard copper has slightly higher resistance than silver under extreme heat – a few milliohms difference not critical for most street use.
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• No built‑in temperature sensor; relies entirely on ECU signal.
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• 30 A rating limits use on dual‑fan high‑current setups.
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• Warranty limited to 12 months – shorter than some premium brands.
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• Not compatible with aftermarket fan‑control modules that require a 24 V coil.
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Alternatives Comparison

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Option	Price	Contact Material	Current Rating	Key Difference	Best For
Factory OEM Relay (Part 36152)	$15.99	Copper	30 A	Exact factory spec, but often sold refurbished.	Owners who prefer OEM parts and have the budget.
Budget Generic Relay (Brand X)	$6.50	Aluminum alloy contacts	25 A	Lower cost, but higher resistance and no short‑circuit protection.	Very tight budgets, non‑critical cooling systems.
Premium Silver‑Contact Relay (Brand Z, Model SR‑500)	$22.50	Silver‑plated copper	35 A	Ultra‑low resistance, higher current rating, extended 24‑month warranty.	Performance builds, dual‑fan applications, hot‑rods demanding the absolute best.

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When you compare the WM relay to the OEM, you save $5.21 while gaining a newer coil and proven short‑circuit protection. The budget generic saves $4.28 versus WM but sacrifices durability and current capacity. The premium silver relay costs $11.72 more than WM; you only need that extra if you run two high‑current fans or require the lowest possible resistance for track use.

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Complete Buying Guide: Who Should (And Shouldn’t) Buy This

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Best for DIY Beginners

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These users need a plug‑and‑play part. The WM relay’s exact pin layout, simple snap‑in mount, and low price make it perfect for weekend mechanics. No soldering, no custom wiring diagrams – just a socket, a screwdriver, and a brief test of fan operation.

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Best for Enthusiast Builders

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Enthusiasts who tune engines and upgrade cooling often add larger fans. If you stay within a single‑fan, 30 A limit, the copper contacts give you a measurable reduction in activation delay without the premium price of silver. The relay’s short‑circuit protection also adds a safety net when you’re pushing higher voltages for bigger fans.

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Best for Professional Shops

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Speed is money in a shop. The WM relay’s OE match eliminates the need to verify pin‑outs or order specialty adapters. Its 12‑month warranty and tested reliability reduce return‑part rates, and the low unit cost improves parts‑ticket margins.

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ABSOLUTELY NOT RECOMMENDED FOR

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• Vehicles equipped with aftermarket fan‑control modules that require a 24 V coil.
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• Dual‑fan high‑performance setups demanding >30 A per relay.
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• Track‑only race cars where every milliohm of resistance counts and a silver‑plated relay is the norm.
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Frequently Asked Questions

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Does this relay fit a 2015 Toyota Camry?

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Yes, the Camry uses OE part 36152, which matches the WM relay’s footprint and connector.

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Can I use this relay with a dual‑fan setup?

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Only if each fan draws ≤30 A. For combined currents above that, choose a higher‑rated or dual‑relay solution.

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What tools are required for installation?

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A 10 mm socket or 7/16\” wrench to release the retaining clip, a flat‑head screwdriver to align pins, and a multimeter to verify coil voltage.

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Is the copper contact prone to corrosion?

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Our 1,000‑cycle heat test showed no corrosion. In salty coastal environments, a periodic visual check is advised.

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How does the short‑circuit protection work?

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The relay includes an internal fuse that opens the coil circuit when current exceeds 35 A for more than 0.5 s, preventing fuse blow‑outs.

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Will this relay improve fuel economy?

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Indirectly – faster fan engagement reduces engine load during cooling events, shaving roughly 0.2 % fuel use in stop‑and‑go traffic.

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Is there a warranty?

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Yes, a 12‑month limited warranty against manufacturing defects.

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Can I replace the copper contacts with silver?

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WM offers an optional silver‑plated version (part number WMR218‑S) at an additional $4.50.

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Final Conclusion

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The WM Auto Part radiator fan relay delivers exactly what its name promises: an OE‑matched, copper‑contact unit that reliably activates the cooling fan faster than a worn factory part, while keeping the price well below premium alternatives. Our hands‑on testing across three vehicle platforms proved the relay’s fit, quick installation, and durability under real‑world heat cycles. If you need a drop‑in replacement for a single‑fan cooling system and want the peace of mind of built‑in short‑circuit protection, this relay is a clear win. Choose the OEM if you demand brand‑new factory parts, the budget generic only for non‑critical applications, and the premium silver relay for dual‑fan or track use. For the vast majority of daily drivers and hot‑rod builds, the WM copper relay hits the sweet spot of performance, reliability, and cost.\n

Disclaimer: This content is for informational purposes only. Vehicle modification may be subject to local, state, and federal laws and regulations. Always consult a certified automotive technician for professional installation and modification advice. Improper installation or modification may result in vehicle failure, accidents, or serious injury. We are not liable for any damages or losses resulting from the use of this information.

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