* Initial Engagement: The fan clutch engages correctly when the engine is first started, indicating the clutch itself *can* function. This is often driven by engine speed, even before the coolant gets hot.
* Disengagement at Normal Operating Temperature: The fan clutch is *supposed* to disengage once the engine reaches normal operating temperature (around 200-210°F for most vehicles). However, yours is disengaging too soon, meaning it's not staying engaged long enough to adequately cool the engine. This is the failure.
* Overheating at 250°F: This confirms insufficient cooling; once the engine reaches 250°F, the system is clearly struggling. At that temperature, significant engine damage is possible.
Possible Causes:
* Failing Fan Clutch: The most likely culprit. The internal mechanism within the clutch that controls engagement based on temperature or engine speed is likely worn or failing. It might not be engaging properly at higher temperatures, even when the engine needs the extra cooling.
* Thermostat Stuck Open (Less Likely): While less likely given the initial engagement of the fan, a thermostat that's stuck open could cause the engine to initially run cooler than normal, leading to the fan disengaging prematurely. However, this would usually still result in overheating eventually, but potentially at a higher temperature than 250°F.
* Coolant Issues (Less Likely): Low coolant levels, a leak, or a clogged radiator could contribute to overheating, but the described behavior points more strongly towards the fan clutch. However, it's worth checking your coolant level and looking for leaks.
* Wiring Issue (Less Likely): A problem with the fan clutch's electrical connection (if it's an electric fan) or the temperature sensor signal could prevent proper fan operation. However, this again is less likely given the initial engagement.
What to Do:
1. Check Coolant Level: Ensure your coolant level is correct and there are no visible leaks.
2. Check Thermostat (Optional): You could check if your thermostat is opening and closing as it should, but this is secondary to the fan clutch issue.
3. Replace the Fan Clutch: Given the symptoms, replacing the fan clutch is the most likely solution to solve your overheating problem. This is a relatively straightforward repair for someone with some mechanical aptitude. You can find replacement fan clutches at auto parts stores, specifying your year and model Trailblazer. Do not drive the vehicle until this is resolved to prevent further engine damage.
Warning: Driving a vehicle with an overheating engine can cause significant and expensive engine damage. Do not continue to drive the vehicle until the problem is diagnosed and repaired. If you are not comfortable performing this repair yourself, take your Trailblazer to a qualified mechanic.
