Method 1: Engine Temperature Check (Most Reliable)
This method requires a reliable way to monitor engine temperature. Ideally, use an infrared thermometer or a scan tool that can read coolant temperature.
1. Start the engine cold: Let the engine run until it reaches normal operating temperature. Monitor the coolant temperature.
2. Check for fan engagement: Once the engine reaches operating temperature (usually around 200-220°F or 93-104°C), the fan clutch *should* engage and the fan should spin relatively quickly.
3. Check for fan disengagement: After the engine cools down significantly (below operating temperature), the fan should spin freely by hand, indicating the clutch is disengaging properly. It shouldn't be locked or require significant effort to turn.
If the fan doesn't engage at operating temperature: The clutch is likely faulty (worn out or seized).
If the fan doesn't disengage when cool: The clutch is likely faulty (seized).
Method 2: Manual Check (Less Reliable)
This method is less precise but gives a general idea of the clutch's condition. It's important to note that this method involves moving parts of a hot engine, so use caution and appropriate safety measures. Wear gloves to avoid burns.
1. Let the engine cool down: Only attempt this after the engine has cooled down considerably.
2. Check for free spin: Try to turn the fan blades by hand. The fan should spin relatively freely. Significant resistance indicates a potentially faulty clutch.
3. Check for engagement at operating temperature (with caution): *After* the engine has reached operating temperature, carefully and briefly try to turn the fan blades again. It should be difficult or impossible to turn, indicating clutch engagement.
Important Considerations:
* Safety First: Always allow the engine to cool down before attempting any manual checks. Hot engine components can cause serious burns.
* Other causes of overheating: A faulty fan clutch is one possible cause of overheating. Other potential culprits include a faulty thermostat, low coolant level, radiator problems, or a failing water pump. Don't automatically assume a bad clutch is the problem until you've ruled out other possibilities.
* Professional Diagnosis: If you're unsure about the results or uncomfortable performing these checks, it's best to take your Blazer to a qualified mechanic for diagnosis.
If you suspect a faulty fan clutch, replacement is usually necessary. It's relatively straightforward to replace, but it requires some mechanical aptitude and the right tools. Consult a repair manual specific to your 1999 Chevy Blazer for detailed instructions.
