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When your engine fan clicks on too late or not at all, the temperature needle creeps toward the red on a hot day. A dedicated thermostat switch and relay fix that by turning the fan on at a set temperature. The best universal cooling fan switch kits bundle everything—relay, probe, fuse, and wiring—into one box you wire in yourself. Here’s what the 185°F on / 175°F off numbers mean, and which kit matches your fan size and electrical comfort level.
I’m Mo Maruf — the founder and writer behind GoCarLife. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
Below are the most reliable kits for wiring a radiator fan to a temperature switch, with honest notes on install difficulty. Find the right universal cooling fan switch for your ride here.
Our Picks at a Glance
How To Choose The Best Universal Cooling Fan Switch
A universal cooling fan switch kit is a small box that makes your electric fan automatic. It reads engine temperature through a probe, then closes a relay to send power to the fan when things get warm. The two numbers you’ll see — like 185°F on / 175°F off — set when the fan kicks in and when it rests.
Match the Relay to Your Fan’s Draw
The relay is rated in amps, most kits here use a 40A relay. That’s enough for a single medium-profile electric fan. If you’re running a high-draw fan or two fans at once, you need a kit rated for the total current, or the relay gets hot and the fuse pops.
Check the Probe Thread and Adapter
The temperature probe usually has a 3/8-inch pipe thread, and a good kit includes a 1/2-inch adapter to fit different ports. You want the probe to thread into the cylinder head or a water jacket so it reads real coolant temperature, not air around the radiator.
Count the Parts in the Box
A complete kit should have the relay, wiring harness, inline waterproof fuse holder, fuses, ring terminals, and wire connectors. Some include a brass adapter for the sending unit. If the box is missing a fuse holder, you’re going to the auto parts store anyway.
Quick Comparison
| Model | Best For | Temp Range | Relay Rating | Wire Length | Amazon |
|---|---|---|---|---|---|
| Dual Electric Fan Relay Kit★ Best Overall | Dual fan conversions | 185°F On / 175°F Off | 40A | 24″ leads | Amazon |
| X AUTOHAUX Electric Fan RelayBudget Champion | Budget single-fan wiring | 185°F On / 175°F Off | 40A | — | Amazon |
| 175-185 Degree Electric Fan Relay Kit | Classic V8 engines | 185°F On / 175°F Off | 60A | — | Amazon |
| 185 To 200 Degree Electric Cooling Fan Kit | Hot climates, trucks | 200°F On / 185°F Off | 50A | — | Amazon |
| 2 PCS Electric Fan Relay Kit | Two fans, one purchase | 185°F On / 175°F Off | 40A | — | Amazon |
| Electric Fan Wiring Kit (ZOZOMOTORS) | Labeled wires, easy install | 185°F On / 175°F Off | 40A | — | Amazon |
| 32-248’F Dial Adjustable Controller | Tunable temperature control | 32°F to 248°F (adjustable) | — | — | Amazon |
In-Depth Reviews
1. Dual Electric Fan Relay Kit 40 AMP with Temperature Switch 185 On 175 Off
Our pick — over 4.5★ from 500+ verified ratings; the strongest balance of quality and price.
The dual-relay kit that gives you room to wire two fans without splicing in a second purchase.
This kit is built for the most common upgrade: swapping a mechanical fan for electric ones. It fits 10, 12, 14, and 16 inch cooling fans, and the 40A relay handles each fan’s draw. The temp switch turns the fan on at about 185°F and off at 175°F, so the engine stays in its happy zone without the fan running constantly.
What you get in the box is a complete wiring set: 40A relay, wiring harness, temperature switch, a 3/8-inch to 1/2-inch adapter, inline waterproof fuse holder, fuses, 8 ring terminals, and 4 wire connectors. Buyers report the leads are generous — one called out the “24” of leads to the relays” as a major convenience, meaning you can route wires up to the battery and sensor without extending anything.
The two things to respect here are the grounding and the thermostat. The temperature switch MUST be grounded through its threads to the engine, and the engine itself must be grounded. Also, the maker says to run a 160°F thermostat with this kit — if your engine thermostat is set at 180°F, the fan may never shut off because the coolant stays too warm. At 8.11 ounces, it’s a light box that tucks into an engine bay neatly.
The Reason It Wins
- Dual relays support two fans cleanly — a huge step up from single-fan kits at this price.
- 24-inch leads to the relays make mounting flexible across engine bays.
- Everything needed is in the box: fuses, terminals, adapters, connectors.
Know Before You Wire
- A 160°F engine thermostat is required — a hotter one keeps the fan running.
- Wiring diagram gets mixed feedback; color codes are labeled but double-check the ground path.
Reach for this if: you’re doing a dual-fan conversion or want a complete single-fan kit with room to grow.
Look elsewhere if: your engine runs a thermostat above 160°F — you’ll have to swap it first.
2. X AUTOHAUX Electric Fan Relay with 185’F On 175’F Off Thread-in Probe 40A
A no-frills 40A kit that gets a single fan running for less than the price of a tank of gas.
This X AUTOHAUX kit is the budget entry point, and it fits the same 10, 12, 14, and 16 inch fans as the pricier kits above. The 185°F on / 175°F off probe threads into the engine head and routes power through the included 40A relay. The wiring is color-coded the same way: red to +12VDC, coffee to fan positive, black to ignition, grey to the sending unit.
The box includes the relay with harness, the thread-in probe, an inline fuse holder, a 20 amp fuse, 4 ring terminals, and 2 fan pigtail connectors. One honest caveat in the manual: the 14AWG wires carry about 15 amps, which the maker says is not enough for high-profile fans that draw heavier current. You’d need to crimp on bigger wire for those.
Owner reports are split in a way you should know about. Some say “works as it should” and call it a nice harness for the money. But there are reported failures where two units didn’t activate fans during engine run, with a replacement also defective. The crowd rating — 4.5 stars across 87 ratings — is still solid, but this is the one kit where a small number of bad units slipped through. It’s a fine choice for a low-amp single fan, not the one to trust for a high-draw setup.
Bottom line: the cheapest way to test an electric fan conversion, but weigh the reliability reports against the savings.
Best if: you need a minimal, low-cost kit for a single low-profile fan and can handle basic wiring.
Think twice if: you’re running a high-profile fan that draws more than 15 amps — the included wire isn’t rated for it.
3. 175-185 Degree Electric Fan Relay Kit Cooling Fan Thermostat Switch Temp Sensor
The 60A relay kit that lists an enormous range of classic V8 engines it directly replaces.
This HHCSOP kit is the one to reach for if you’re resurrecting an older American V8. The fitment list is long — 265, 283, 305, 307, 327, 350, 383, 400, 396, 402, and dozens more, from small-blocks to big-blocks like the 427, 454, and 460. The probe is a 3/8″ NPT thread, and a brass adapter is included to install the sending unit. It turns the fan on at 185°F and off at 175°F, and works with any 12-volt system.
This kit’s relay is rated at 60A (amperes, a measure of electrical current), the most sturdy in this lineup. That gives you real headroom for a single high-profile fan or a pair of smaller ones without worrying about overheating the contacts. The package includes wires, relay switch, circuit breaker, terminals, and mounting screws.
The common refrain from owners is that it makes wiring a fan “much easier” and functions as expected, with a note that it has held up well over time. The recurring friction is documentation — some say the wiring diagram is marginal, and there are no instructions in the box. One owner wired it wrong initially because of that, then figured out the thermostatic switch goes to the grounding wire on the relay’s terminal 86. This is a strong, high-current kit if you already understand relay grounding.
Strongest point: the 60A rating gives it the biggest safety margin in this list; bring your own wiring knowledge since the diagram is thin.
Grab this for: classic V8 swaps or any fan that pushes serious current.
skip it if: you’re a first-time wire-r — you’ll want a kit with clearer instructions.
4. 185 To 200 Degree Electric Cooling Fan Kit Thermostat Switch Temperature Fan Wiring Kit
The 200°F-triggered kit that keeps big trucks cool through brutal summer heat without constant fan noise.
Here’s a twist on the usual temperature settings: this kit turns the fan on at 200°F and off at 185°F, a higher threshold that suits trucks and hot climates where engines run warm by design. It fits 7, 10, 12, 14, and 16 inch fans with a 3/8″ pipe thread NPT probe, and the relay is rated at 50A. The same huge list of compatible engines applies — 265 through 460, covering classic small-blocks and big-blocks.
Owners have put this kit through real punishment. The standout story is a Jeep Cherokee XJ that kept cool in Texas heat, with the sensor triggering around 185°F and the harness working as promised. Another user added it as a condenser fan to a truck for hot summer temps, and it worked perfectly. The kit includes a brass adapter for the sending unit, wires, relay switch, circuit breaker, terminals, and mounting screws.
The honest friction: directions are poor for electrical newcomers, especially if you also want a rocker switch in the loop. One owner needed online help to wire a 4-pin rocker switch in, and noted the red wire wasn’t long enough for their routing. The supplier stands behind it though — if it fails, cracks, or stops working, they promise a satisfactory answer within 12 working hours. At 10.8 ounces, it’s the heaviest kit here, mostly because of the beefier relay.
Who it’s for: truck owners and hot-climate drivers who want fans that don’t run until the engine is genuinely warm.
Choose this if: you run a truck or live somewhere summer pushes coolant temps well past 200°F.
Pass if: you want a fan that kicks on earlier — the 185°F-on kits fit that need better.
5. 2 PCS Electric Fan Relay Kit, Dual Electric Fan Relay Kit, 185 On 175 Off
Two complete 40A kits in one box, ideal for a pair of 14-inch electric fans on a big SUV.
This ecocstm pack is two full relay kits, each with a 40A relay, harness, 3/8-inch to 1/2-inch adapter, 20 amp fuse, fuse holder, ring terminals, and wire connectors. The appeal is clear: one purchase wires both fans on a truck or SUV, and it fits 10, 12, 14, and 16 inch cooling fans. An owner used it for dual 14-inch e-fans on a 97 Suburban and called the install easy.
The build quality gets specific praise. The housing is high-temperature resistant nylon with a waterproof design rated IP56 — meaning it’s protected against powerful water jets, a real plus for a part mounted low in an engine bay. The wiring uses 14AWG with all-copper (purple copper) conductors and a PVC wrap for flexibility. The thermostat opens at 185°F and closes at 175°F, and it must be earthed through its thread to the engine.
The honest caveat comes from a heavy-duty user who found these hobby-grade for high-amp engine fans, reporting popped fuses under real load. For a standard dual 14-inch e-fan setup on a street vehicle, most owners are satisfied. But if you’re pushing large, high-draw fans hard, this budget multi-pack may not be the last relay you buy.
What the Pack Delivers
- Two complete kits — no second order for a dual-fan conversion.
- IP56 waterproof rating protects against spray and jets.
- Copper-core 14AWG wiring stays flexible and conducts well.
The Trade-Off
- A heavy-draw user reported blown fuses under real engine load.
- Best suited to standard street fans, not extreme high-amp setups.
Reach for it when: you’re wiring two moderate electric fans and want it done in one purchase.
Think twice if: you’re running large, high-amperage fans that will push the 40A relay and fuse hard.
6. Electric Fan Wiring Kit Electric Fan Relay Kit with Thermostat Radiator Fan Sensor Switch
The ZOZOMOTORS kit whose clearly labeled wires make first-time fan wiring genuinely approachable.
This is the kit to buy when the idea of reading a wiring diagram makes you nervous. Every wire is labeled and color-coded — red to the 12VDC positive battery terminal, coffee to fan positive, black to sending unit, grey to ignition — and a diagram is included in the package. It fits 10, 12, 14, and 16 inch fans, and the 40A relay is enough for a medium or low-profile electric fan. The temp switch turns on near 185°F and off at 175°F.
Owners describe installation as straightforward even with basic electrical experience, and several note it’s great value — no need to buy a big-name brand for a fan relay. One upgrade story: it worked perfectly on an 87 Samurai. That owner’s strong warning: you MUST use the temp sensor included, it will not work with the factory sensor. That’s a critical detail for conversions.
There’s a documented wiring-diagram quirk worth flagging. Several owners found the fan wouldn’t run until they realized the diagram has an error — the black wire should go to the thermostat switch and the white wire to the ignition, not the other way around. Once that’s corrected, the kit works. The box includes the 40A relay, harness, temperature switch, 3/8-inch to 1/2-inch adapter, inline waterproof fuse holder, fuses, 1 spade connector, 4 ring terminals, and 2 wire connectors. For high-profile fans, the maker points you to their heavier relay kit or a 10-gauge wire upgrade on pins 30 and 87.
Why it earns its spot: the clearest labels in the category make it the lowest-stress install, with a one-line wiring fix if the fan stays silent.
Best for: DIYers doing their first electric fan conversion who want labeled wires and a forgiving learning curve.
Not for: high-profile fans drawing heavy current — plan a wire upgrade on pins 30 and 87.
7. 32-248’F Dial Adjustable Electric Radiator Cooling Fan Thermostat Controller Switch
A dial you turn instead of a fixed switch, letting you set the fan trigger anywhere from 32°F to 248°F.
This American Volt controller is the most flexible option because you’re not locked into a fixed temperature. A mechanical dial sets the turn-on anywhere from 32°F to 248°F (0°C to 120°C), so you decide when the fan kicks in. That’s a huge advantage for a custom build or a vehicle with unusual cooling needs. The probe reads liquid or contact temperature and passes power to the fan.
Installation is different from the fixed kits — the probe mounts between radiator fins or inside a radiator or oil cooler hose, rather than threading into the engine block. The 3-pin setup lets you wire it as either a normally open or normally closed circuit, which gives flexibility for how your fan system is built. It weighs just 4 ounces, a featherweight box that’s easy to position.
The catch is mounting. Several owners note the bracket isn’t included, and you’ll need to make a plate to hold the dial. One RV owner made a pair of 1/8-inch aluminum plates to mount theirs. Oddly, the same owner ran these in a completely different role — controlling rooftop solar inverter heat-sink temperature — which shows how adaptable the probe is. The highest praise is for the functionality: being able to adjust when the fan comes on “to whatever you want.”
The standout: no other kit here lets you fine-tune the trigger temperature on a whim — perfect for a project car you keep tweaking.
Pick this if: you want dial-in control over fan temperature, or you’re cooling something other than an engine.
Know this: it doesn’t ship with a mounting bracket — plan to fabricate a small plate.
Understanding the Specs
185°F On / 175°F Off
These numbers tell you when the fan starts and stops. The “on” temperature is what the coolant must reach before the switch closes and runs the fan. The “off” is when it lets the fan rest. A 185°F on / 175°F off switch keeps a standard engine cool. The 200°F on / 185°F off kit suits trucks that run warm without needing the fan on early.
40A vs 60A Relay Rating
The relay is the switch that carries the fan’s actual current. A 40A relay handles a typical medium-profile electric fan. A 60A relay has more headroom for high-draw fans or multiple fans. If the relay is too small, it heats up and the fuse pops. Match the relay rating to the total current your fan draws.
The Ground Path
Most temp switches work with a 12-volt system by grounding through their mounting threads into the engine. That means the threads must be clean and tight, and the engine itself must be grounded to the battery. A poor ground is the most common reason a fan never turns on.
FAQ
What does a universal cooling fan switch do?
Will a switch that turns on at 185°F work with my engine?
How do I install the temperature probe?
What size relay do I need for my electric fan?
Can I use one kit to run two fans?
Why won’t my fan turn on after wiring the kit?
Can I adjust when the fan turns on?
Can the probe mount anywhere besides the engine block?
Final Thoughts: The Verdict
If you want one dependable pick, the best universal cooling fan switch is the Dual Electric Fan Relay Kit because its dual 40A relays, 24-inch leads, and complete parts list handle both single and dual-fan builds out of one box. If you want a 60A relay with huge classic V8 fitment, grab the 175-185 Degree Electric Fan Relay Kit. And for dial-in control that adapts to any cooling situation, the 32-248’F Dial Adjustable Controller is the one to reach for.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of August 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
As an Amazon Associate, GoCarLife earns from qualifying purchases. This does not affect which products we feature.