How to Tell If Your Car’s Thermostat Is Stuck

A faulty thermostat might seem minor, but it can lead to serious engine damage if not addressed. Your car’s thermostat regulates engine temperature by controlling coolant flow. If it gets stuck open or closed, your engine either won't warm up properly or may overheat—both dangerous situations. Here’s how to spot the signs early.

Why the Car's Thermostat Matters

The thermostat opens and closes based on the engine’s temperature. When it’s working right, your engine warms up quickly and stays within an optimal range. A stuck thermostat disrupts that balance, which can result in poor fuel efficiency or engine failure.

Common Signs of a Stuck Thermostat

1. Engine Overheating

• A stuck-closed thermostat prevents coolant from circulating, causing the engine to overheat quickly.

• You might see the temperature gauge rising rapidly soon after starting the vehicle.

2. Poor Heater Performance

• If the thermostat is stuck open, the engine might never reach proper operating temperature.

• Your cabin heater may blow cold air, even after driving for a while.

3. Fluctuating Temperature Gauge

• Watch your dashboard’s temperature needle.

• A thermostat that opens or closes unpredictably may cause temperature swings.

4. Unusual Coolant Levels

• A stuck thermostat can create pressure issues in the cooling system.

• You may find the coolant reservoir unusually full or completely empty, depending on the issue.

5. Check Engine Light

• Modern vehicles can detect temperature irregularities.

• A diagnostic code may point to cooling system issues or poor engine efficiency.

What to Do If You Suspect an Issue

If you notice one or more of these signs:

1. Stop driving if the engine is overheating.

2. Check your coolant level once the engine is cool.

3. Schedule an inspection with a professional mechanic.

At DM Motorsports in Midland Mint Hill, NC, we specialize in diagnosing and fixing cooling system problems. We’ll let you know if your thermostat is to blame and get your vehicle back to safe operating condition—without pushing unnecessary repairs.

Prevent Bigger Problems

A stuck thermostat can lead to a blown head gasket or warped engine components. Addressing it early can save hundreds—or thousands—on repairs.