Learning how to change the thermostat in a car is a valuable intermediate repair skill that can save you money and prevent a simple issue from becoming a major problem. A malfunctioning thermostat can cause overheating or prevent your engine from reaching its proper operating temperature, both of which lead to poor performance and potential damage.
This guide provides clear, step-by-step instructions for this common repair. With some basic tools and a few hours, you can complete this job yourself and gain confidence in maintaining your vehicle.
How To Change The Thermostat In A Car
Replacing a car thermostat involves locating it, safely draining some coolant, removing the housing, swapping the unit, and refilling the system. While the specific steps vary slightly by vehicle make and model, the core process remains largely the same for most cars and trucks. Always consult your vehicle’s service manual for the most accurate, model-specific information.
Tools And Materials You Will Need
Gathering the right tools before you start is crucial for a smooth process. Having everything on hand will prevent frustrating interruptions. Here is a basic list to get you started.
- A new thermostat (ensure it’s the correct part for your specific vehicle)
- New thermostat housing gasket or O-ring (often included with the thermostat)
- A gallon of the correct type of coolant for your car
- Distilled water (for mixing if required)
- A drain pan or bucket (at least 2-gallon capacity)
- Basic socket set and ratchet with extensions
- Screwdrivers (flathead and Phillips)
- Pliers (channel-lock or adjustable)
- A funnel
- Rags or shop towels
- Safety glasses and gloves
- Jack and jack stands (if the thermostat is in a low position)
Safety Precautions Before You Begin
Your safety and the safety of your vehicle’s engine are the top priorities. Never work on a hot engine. The coolant system is under pressure and contains extremely hot fluid that can cause severe burns.
Essential Safety Steps
- Allow the engine to cool completely overnight or for several hours. The radiator and upper hose should be cool to the touch.
- Always disconnect the negative battery cable before begining any work to prevent any accidental electrical shorts.
- Work in a well-ventilated area as coolant fumes can be unpleasant.
- Wear safety glasses to protect your eyes from coolant splash.
- Have a container ready for old coolant and dispose of it properly at a recycling center; it is toxic to animals and the environment.
Step-By-Step Replacement Guide
Follow these steps in order to successfully replace your car’s thermostat. Take your time and refer to your vehicle’s manual for any specific torque specifications or unique steps.
Step 1: Locate The Thermostat Housing
The thermostat is always housed somewhere along the upper coolant hose that runs from the engine to the radiator. The most common location is where this hose connects to the engine, often on the engine block or intake manifold. Follow the upper radiator hose from the radiator back to the engine; the housing is typically a metal or plastic casing with two or more bolts.
Step 2: Drain The Coolant
You need to drain enough coolant from the system to lower the level below the thermostat housing. This prevents a large spill when you open the housing.
- Place your drain pan underneath the radiator’s drain plug or the lower radiator hose connection.
- Carefully open the drain plug or loosen the lower hose clamp to allow coolant to flow into the pan. Only drain about one-third to one-half of the total system capacity.
- Once drained, close the drain plug or re-tighten the hose clamp securely.
- For some vehicles, you may need to remove the radiator cap to allow the coolant to drain properly.
Step 3: Remove The Thermostat Housing
This is the core mechanical step. Be careful not to damage the housing, especially if it is made of plastic.
- Use a screwdriver or socket to loosen the clamp on the upper radiator hose where it connects to the thermostat housing.
- Slide the hose off the housing neck. Some coolant may drip out; this is normal.
- Using the correct socket, remove the two or more bolts securing the thermostat housing to the engine.
- Gently pry the housing loose. You may need to tap it with a rubber mallet if it’s stuck from old gasket material.
- Lift the housing away to reveal the old thermostat inside its seat.
Step 4: Remove The Old Thermostat And Clean The Surface
Take a moment to inspect the old thermostat and the housing area. This can give you clues about the systems condition.
- Lift the old thermostat straight out of its seat.
- Use a plastic scraper or a rag to thoroughly clean all the old gasket material from both the engine mounting surface and the thermostat housing. Ensure the surfaces are smooth and clean for a proper seal with the new gasket.
- Check the old thermostat. If it’s stuck open, the car would run cool. If it’s stuck closed, it would cause overheating. Jiggling it should reveal if the valve moves freely.
Step 5: Install The New Thermostat
Installation is the reverse of removal, but attention to detail is key. A common mistake is installing the thermostat backwards, which will cause immediate failure.
- Place the new gasket or O-ring onto the housing or the engine block, depending on the design. You may use a tiny bit of coolant as a lubricant to help it stay in place.
- Insert the new thermostat into its seat. The critical part: the spring side of the thermostat goes INTO the engine. The valve or flange faces outward toward the radiator hose. A phrase to remember is “the spring goes in the engine.”
- Carefully position the housing back over the thermostat and onto the engine mounting surface.
- Hand-tighten the housing bolts to hold it in place.
Step 6: Reassemble And Refill The Cooling System
With the new thermostat securely in place, you can begin putting everything back together and refilling the system.
- Using a torque wrench if possible, tighten the thermostat housing bolts in a criss-cross pattern to the specification in your manual. Overtightening, especially on plastic housings, can cause cracks.
- Slide the upper radiator hose back onto the housing neck and tighten its clamp securely.
- Reconnect the negative battery cable.
- With the drain plug closed, use a funnel to slowly pour a 50/50 mix of fresh coolant and distilled water into the radiator or coolant overflow reservoir until it reaches the “Full” line.
- Replace the radiator cap or reservoir cap securely.
Step 7: Bleed The Cooling System And Check For Leaks
This final step is essential to remove air pockets from the system, which can cause overheating even with a new thermostat.
- Start the engine with the heater set to maximum heat and fan on low. This opens the heater core to coolant flow.
- Allow the engine to idle and warm up. Watch the temperature gauge; it should rise to the normal operating range and then stabilize.
- As the engine warms, the thermostat will open. You will see the coolant level in the radiator or reservoir drop as the system purges air. Add more coolant mixture as needed to maintain the proper level.
- Once the engine is at full operating temperature and the heater is blowing hot air, the system is likely bled. Turn off the engine and let it cool completely.
- After it cools, check the coolant level one more time and top it off if necessary. Inspect the thermostat housing area and hose connections for any signs of leaks.
Testing The New Thermostat
After the repair, take the car for a short, careful test drive. Monitor the temperature gauge closely. It should rise to the normal midpoint and stay there consistently. The heater should produce strong, hot air. If the gauge climbs too high or stays too low, you may have an air pocket, a faulty new thermostat, or another issue.
Common Mistakes To Avoid
Being aware of these common errors can help you achieve a successful repair on your first try.
- Installing the thermostat backwards. Always remember: spring goes into the engine.
- Forgetting to install the new gasket or reusing the old one, which will cause a leak.
- Overtightening the housing bolts and cracking the housing.
- Not properly bleeding the cooling system of air.
- Using the wrong type of coolant, which can cause chemical reactions and damage.
- Failing to dispose of the old coolant responsibly.
When To Call A Professional Mechanic
While this is a manageable DIY job, some situations warrant professional help. If you encounter severe corrosion, a broken housing that needs replacement, or if you complete the repair and the car still overheats, it’s time to consult a mechanic. They have the tools and expertise to diagnose more complex cooling system issues like a failing water pump or a blocked radiator.
Frequently Asked Questions
How Do I Know If My Car Thermostat Is Bad?
Signs of a bad thermostat include the engine overheating, the engine taking too long to warm up (staying cold), fluctuating temperature gauge readings, and poor heater performance. Coolant leaks around the thermostat housing are also a common indicator.
What Is The Average Cost To Replace A Thermostat?
If you do it yourself, the cost is typically just the price of the thermostat and coolant, usually between $30 and $80. At a repair shop, the total cost for parts and labor can range from $150 to $400 depending on the vehicle’s make and model and the shop’s labor rates, as the job can take 1-2 hours.
Can You Drive With A Faulty Thermostat?
It is not recommended. A thermostat stuck closed will cause rapid overheating and can lead to catastrophic engine damage like a warped cylinder head or blown head gasket. A thermostat stuck open causes the engine to run too cool, reducing fuel efficiency and increasing engine wear over time.
How Long Does It Take To Change A Thermostat?
For a novice with all the tools ready, the job can take between 1.5 to 3 hours. This includes time for the engine to cool, the repair itself, and the crucial system bleeding process. An experienced person can often complete it in under an hour.
Should I Replace The Thermostat Housing Too?
It depends on its condition. If the housing is metal and in good shape, you usually don’t need to. However, if it’s plastic, cracked, or heavily corroded, it’s wise to replace it while you have the system apart. Many new thermostats come with a new housing or gasket kit.