1. Check the Obvious:
* Engine Temperature: Is the engine overheating? A properly functioning cooling system should eventually bring the engine to operating temperature even without the fans. If the engine is overheating *despite* the fans not working, that's a critical issue requiring immediate attention (to avoid engine damage). Use a reliable temperature gauge; the dash gauge might be inaccurate.
* Fuse(s): Check the fuse(s) related to the radiator fans in the fuse box. The owner's manual should specify their location and amperage. Replace any blown fuses.
* Relay(s): Many systems use relays to switch high-amperage circuits. Your DeVille likely has one or more relays for the fans. Locate these relays (often near the fuse box or under the hood). You can often hear a click when a relay engages. Try swapping a known good relay (same amperage) with a suspect relay to see if that resolves the issue.
* Fan Motors: With the ignition on, carefully try to spin each fan motor by hand. If they're seized or very stiff, the motor itself is likely faulty and needs replacement.
2. Electrical Testing (Requires a multimeter):
* Power at the Fan(s): With the ignition on and the engine at operating temperature (or by using a jumper wire to trigger the fan's thermal switch – see below), check for power at the fan's connector. You should have power (battery voltage) at one wire; the other will be ground. If there's no power, the problem is upstream of the fan motor itself.
* Power at the Relay: Similarly, check for power at the relay's input and output terminals (refer to a wiring diagram). If power isn't reaching the output side, the relay itself or the control circuit is the problem.
* Circuit Continuity: Using a multimeter, test the wiring between the fan, relay, and any temperature sensors. Look for broken wires, poor connections, or high resistance in the circuit.
* Temperature Switch (Thermostat Switch): Locate the temperature switch (often near the radiator). This switch activates the fans when the coolant reaches a certain temperature. You can test this switch with a multimeter by checking its continuity at different temperatures. A jumper wire can be temporarily used across the switch's terminals to simulate the closed position of the switch. This will allow you to isolate if the sensor itself is functioning correctly.
* Cooling Fan Control Module (if applicable): Some systems use a dedicated control module. If your DeVille has one, it will need to be tested or replaced. This requires more advanced diagnostics and often a wiring diagram.
3. Advanced Diagnostics:
* Wiring Diagram: A wiring diagram specific to your 1987 Cadillac Coupe DeVille is invaluable. It will show you the exact path of the electrical circuits and help identify components and their locations. You can often find these online (through forums dedicated to classic Cadillacs) or at a parts store.
* Professional Help: If you're not comfortable with electrical testing or don't have the necessary tools, it's best to take your car to a qualified mechanic. They have the expertise and equipment to diagnose the problem efficiently.
Safety Precautions:
* Always disconnect the negative battery cable before working on any electrical components.
* Be careful when working near the radiator and engine; they can be hot.
* Use caution when testing electrical components with a multimeter; incorrect use can damage your equipment or cause injury.
By following these steps systematically, you should be able to narrow down the cause of your inoperative radiator fans and determine the necessary repair. Remember, if you are unsure about any step, consult a professional mechanic.
