The cooling fan relay part number for a 1987 C4 Corvette is 14089157, made by AC Delco, which is the original equipment manufacturer (OEM) part.

This relay controls the electric cooling fan that pulls air through the radiator when the engine temperature rises. If your fan runs constantly, won't turn on when the engine is hot, or cycles erratically, the relay is often the culprit — it's cheaper to replace than the fan motor itself and a common wear item on C4s that are now 35+ years old.

The relay mounts in the fuse box under the hood on the driver's side. You can test it before replacing by listening for a click when the engine reaches operating temperature, or by swapping it temporarily with another relay of the same type to see if the symptom moves to a different circuit.

Key Takeaways

  • The OEM part number is 14089157 (AC Delco), and aftermarket equivalents are widely available at auto parts stores for $15 to $35.
  • The relay sits in the underhood fuse box on the driver's side and can be pulled straight out without tools.
  • A bad relay usually causes the fan to run all the time, not run at all, or cycle on and off without pattern.
  • Replacement takes 30 seconds once you locate the relay; no special tools or knowledge of wiring is needed.

Where the relay sits and how to identify it

Open your hood and look at the fuse box mounted on the driver's side of the engine bay, near the firewall. The box is a black plastic module with a removable cover. Inside, you'll see a row of fuses and several relays — the relays are larger, cube-shaped components, usually about 1.5 inches on each side.

The cooling fan relay is typically labeled on the inside of the fuse box cover or in your owner's manual. On a 1987 C4, it's often in one of the corner positions. If the cover diagram is worn or missing, you can identify it by the part number stamped on the relay itself — look for 14089157 or a similar AC Delco number.

Testing before you replace

Start the engine and let it idle until the temperature gauge moves into the normal range. Listen near the fuse box for a distinct clicking sound — that's the relay energizing. If you hear nothing and the fan isn't running, the relay is likely bad. If the fan runs constantly even when the engine is cold, the relay may be stuck closed.

A quick swap test works well: pull the cooling fan relay out and replace it temporarily with another relay of the same size from the fuse box (the horn relay or fuel pump relay, for example). Start the engine again. If the symptom moves to that other circuit — say, the horn stops working — then your original relay is bad. Swap them back and order a replacement.

Replacement and part sourcing

The relay pulls straight out of its socket with no tools required. Grasp it firmly and pull straight up. The new relay pushes in the same way — align it and press down until you feel it seat. The whole job takes less than a minute.

AC Delco 14089157 is the OEM part and costs $20 to $35 at most auto parts chains. Equivalent aftermarket relays from Standard Motor Products, Bosch, or other suppliers run $15 to $25 and work identically. Any relay rated for the same amperage and voltage will function, though the OEM part carries the factory warranty and is may provide to match the original specifications.

Why C4 cooling fan relays fail

The relay is an electromechanical switch — it uses a small electromagnet to pull a metal contact arm that completes the circuit to the fan motor. After 35 years, the contacts inside corrode or wear, the electromagnet coil develops resistance, or the mechanical arm sticks. Unlike a fuse, which straightforward burns out, a relay can fail in several ways: it may not energize at all, stick in the on position, or cycle unpredictably.

Heat and vibration accelerate the process. The underhood environment is harsh, and the relay cycles thousands of times over the life of the car. Replacement is preventive maintenance on any C4 that's been on the road since the 1980s.

Related components to check if the relay isn't the problem

If you replace the relay and the fan still doesn't work, the issue lies elsewhere in the circuit. Check the fan motor itself by explore 12 volts directly to it with jumper cables — if it spins, the motor is good and the problem is in the wiring or the temperature sensor. If the motor doesn't spin, it's burned out and needs replacement.

The temperature switch (or coolant temperature sensor) tells the relay when to turn on. On a 1987 C4, this is a straightforward switch that closes at a set temperature. If it's stuck open, the relay never receives the signal to energize. You can test it by unplugging it and checking continuity with a multimeter when the engine is hot — it should show continuity (zero ohms) at operating temperature.

Frequently Asked Questions

Can I drive the car if the cooling fan relay is bad?

Yes, but only if the fan is stuck running constantly. If the fan won't run at all, the engine will overheat, especially in traffic or on hot days. Stop driving and replace the relay before the engine temperature climbs into the red zone.

Is there a difference between the 1987 relay and relays from other C4 model years?

The relay part number remained 14089157 throughout most of the C4 generation (1984–1996), so a relay from a 1990 or 1992 C4 will work in your 1987. Always verify the part number on the relay itself before installing it.

What if the relay clicks but the fan still doesn't run?

The relay is working, but the fan motor or the wiring between the relay and the motor is bad. Test the fan motor directly with jumper cables connected to the battery. If it doesn't spin, the motor is burned out. If it does spin, check the wiring harness for corrosion or loose connections.

Do I need to disconnect the battery before replacing the relay?

No. The relay is a low-voltage component and pulling it won't cause a shock or short. However, disconnecting the negative battery terminal is always safe practice if you're uncomfortable working around live circuits.

Where can I buy the 14089157 relay?

Any auto parts chain — AutoZone, O'Reilly, NAPA, Advance Auto Parts — stocks this relay or an equivalent. You can also order it online from Amazon or eBay. Expect to pay $15 to $35 depending on the brand and whether you choose OEM or aftermarket.