Your car’s thermostat might be small, but it plays a big role in how your engine performs. When it’s working correctly, your engine warms up quickly and stays at the ideal operating temperature. But when it fails, it can lead to serious problems like overheating, poor fuel economy, or even total engine failure.
At Federal Way Automotive, we regularly see vehicles come in with overheating issues — and more often than not, a faulty thermostat is the root cause. In this post, we’ll break down what your thermostat does, how to recognize when it’s going bad, and why it’s critical to catch this issue early.
What Does the Thermostat Do?
The thermostat is a temperature-controlled valve that sits between your engine and the radiator. Its job is simple but essential:
- When the engine is cold, the thermostat stays closed to help the engine warm up faster.
- Once the engine reaches the proper temperature, the thermostat opens to let coolant flow through the radiator and regulate heat.
By opening and closing at the right times, the thermostat keeps your engine running within a specific temperature range — not too cold, and definitely not too hot.
What Happens When the Thermostat Fails?
Thermostats usually fail in one of two ways — either stuck closed or stuck open. Each one leads to different problems.
If It’s Stuck Closed
A stuck-closed thermostat prevents coolant from flowing into the radiator. This traps heat in the engine and causes it to overheat rapidly. If ignored, this can lead to:
- Boiling coolant
- Blown head gasket
- Warped cylinder head
- Complete engine failure
This is one of the most dangerous types of failures, and it can happen without much warning.
If It’s Stuck Open
A stuck-open thermostat lets coolant flow all the time, even when the engine is cold. This prevents the engine from warming up properly and leads to:
- Poor fuel economy
- Rough idle or reduced performance
- Weak heat from the cabin heater
- Excessive engine wear in cold weather
While this won’t immediately destroy the engine, it will shorten its lifespan and lead to long-term drivability issues.
Signs Your Thermostat Might Be Failing
Thermostats usually don’t fail completely out of the blue — there are warning signs. If you notice any of the following, it’s worth getting your cooling system checked:
- Temperature gauge rising above normal or fluctuating
- Coolant boiling or leaking from the reservoir
- Poor heater performance in the cabin
- Check engine light (especially with cooling-related codes)
- Car takes too long to warm up or warms up too quickly
Some failures happen slowly, while others are sudden — especially in hot weather or when towing.
Can a Bad Thermostat Cause Engine Failure?
Yes — especially if it’s stuck closed and the driver continues to drive while the engine is overheating. Your engine can only tolerate so much heat before metal parts start to warp, seals break down, and internal damage occurs.
In severe cases, thermostat failure has led to:
- Cracked engine blocks
- Seized engines
- Complete loss of cooling system pressure
That’s why it’s critical to pull over immediately and shut off the engine if you see the temperature rising into the red zone.
How Thermostat Failure Gets Misdiagnosed
One of the reasons thermostat problems get overlooked is because the symptoms can mimic other issues:
- A stuck-open thermostat might be mistaken for a bad heater core
- Overheating might be blamed on a radiator, water pump, or coolant leak
- Erratic temperature readings might seem like a sensor issue
At Federal Way Automotive, we perform full cooling system diagnostics to make sure we get to the root cause. If the thermostat is to blame, we’ll replace it with a high-quality part and test the system to ensure proper function.
Preventing Thermostat Problems
There’s no set mileage when a thermostat will fail, but many last between 80,000–120,000 miles. You can extend its life by:
- Maintaining proper coolant levels
- Flushing the cooling system at regular intervals
- Using the correct type of coolant for your vehicle
- Replacing the thermostat as part of major cooling system repairs (like water pump or radiator service)
If your vehicle is approaching the 100,000-mile mark or showing signs of irregular engine temps, now’s a good time to have it checked.
Reliable Cooling System Repair in Federal Way, WA
If your temperature gauge is acting up or your engine has started running hotter than normal, don’t ignore it. A failed thermostat can go from a $200 repair to a $5,000 engine replacement in a matter of minutes.
At Federal Way Automotive, we’ve been keeping drivers in Federal Way, Tacoma, Fife, Milton, and Edgewood safe and on the road for over 35 years. Our ASE-certified technicians will diagnose your cooling system issues and recommend only the repairs you truly need.
📞 Call us today or schedule your appointment online. We’ll help you stop a small problem before it becomes a big one.
