How Do You Replace the Thermostat on a Subaru Impreza?

When it comes to maintaining the reliable performance of your Subaru Impreza, ensuring that every component functions smoothly is essential. One often overlooked but critical part of your vehicle’s cooling system is the thermostat. The thermostat plays a vital role in regulating engine temperature, helping your Impreza run efficiently and preventing overheating or excessive wear. Understanding when and how to replace this small yet significant component can save you from costly repairs and keep your car running at its best.

Replacing the thermostat in a Subaru Impreza is a task that many car owners can approach with confidence once they grasp the fundamentals. It involves more than just swapping out a part; it’s about recognizing the signs of a failing thermostat and appreciating its impact on engine health. Whether you’re a seasoned DIY enthusiast or a curious Subaru owner, gaining insight into this maintenance procedure empowers you to make informed decisions about your vehicle’s care.

In the sections that follow, we’ll explore the importance of the thermostat, common symptoms indicating it might be time for a replacement, and a general overview of what the replacement process entails. This knowledge will equip you with the understanding needed to keep your Subaru Impreza running smoothly through every season and mile.

Identifying the Thermostat Location and Preparation

The thermostat on a Subaru Impreza is typically located near the engine block, connecting the engine to the radiator via the upper radiator hose. To access it, first ensure the vehicle is parked on a level surface with the engine cool to prevent burns or other injuries.

Begin by opening the hood and locating the upper radiator hose, which runs from the radiator to the engine. The thermostat housing is usually found where this hose connects to the engine. It is a small metal or plastic casing secured by bolts.

Before beginning the replacement process, gather the necessary tools and materials:

• Socket set and ratchet
• Screwdrivers
• Pliers
• Drain pan
• New thermostat and gasket/seal
• Coolant (matching the vehicle’s specifications)
• Clean rags or shop towels
• Torque wrench (recommended)

It is also advisable to consult the vehicle’s service manual for any model-specific instructions or torque specifications related to the thermostat housing bolts.

Draining the Coolant and Removing the Thermostat Housing

To avoid spillage and potential damage, the coolant must be drained to a level below the thermostat housing before removal. Locate the radiator drain plug at the bottom of the radiator and place a drain pan underneath. Open the drain plug carefully and allow the coolant to flow out.

Once the coolant level is sufficiently lowered, close the drain plug to prevent further loss. Loosen the hose clamp on the upper radiator hose using pliers or a screwdriver, then carefully detach the hose from the thermostat housing. Some coolant may still be present in the hose, so have rags ready to catch any drips.

Next, remove the bolts securing the thermostat housing to the engine block. Gently lift the housing away, exposing the thermostat. Take note of the orientation of the thermostat for correct installation of the new part. The thermostat typically has a spring side and a flange side which must align properly to ensure correct operation.

Replacing the Thermostat and Reassembling

Carefully remove the old thermostat and discard it. Clean the mating surfaces on both the engine block and thermostat housing to remove any gasket material, dirt, or corrosion. This ensures a proper seal and prevents leaks.

Place the new thermostat into the engine block, ensuring it matches the original orientation. Install a new gasket or apply the recommended sealant to the thermostat housing as specified by the manufacturer. Reattach the thermostat housing and tighten the bolts evenly to the specified torque.

Reconnect the upper radiator hose and secure it with the hose clamp. Double-check all connections to ensure they are tight and secure.

Refilling the Cooling System and Bleeding Air

Refill the radiator with the appropriate type and mixture of coolant, as recommended for the Subaru Impreza. Using the correct coolant prevents corrosion and maintains optimal engine temperature regulation.

After refilling, it is critical to remove any trapped air within the cooling system to avoid overheating or improper thermostat function. To bleed the system:

• Start the engine and let it idle with the radiator cap off.
• Turn the heater to maximum temperature and fan speed to allow coolant to circulate fully.
• Watch for air bubbles escaping from the radiator neck.
• Add coolant as necessary to maintain proper level.
• Once air bubbles stop and the coolant level stabilizes, replace the radiator cap securely.

Monitor the engine temperature gauge during this process to ensure the thermostat opens at the correct temperature and the cooling system operates properly.

Step	Action	Tips
Locate Thermostat	Find upper radiator hose connection to engine	Consult service manual for exact location
Drain Coolant	Open radiator drain plug and collect coolant	Wear gloves and dispose coolant properly
Remove Housing	Detach hose and unscrew thermostat housing bolts	Note thermostat orientation
Replace Thermostat	Install new thermostat with new gasket	Clean mating surfaces thoroughly
Refill and Bleed	Refill coolant and remove trapped air	Monitor temperature gauge closely

Signs Indicating the Need for Subaru Impreza Thermostat Replacement

Proper thermostat function is critical for maintaining the Subaru Impreza’s engine temperature within optimal operating range. Failure to replace a faulty thermostat can lead to engine overheating or inefficient heating. Key symptoms indicating a thermostat replacement is necessary include:

• Engine Overheating: A stuck-closed thermostat prevents coolant circulation, causing rapid temperature rise.
• Engine Running Too Cold: A thermostat stuck open keeps the engine from reaching ideal operating temperature, reducing fuel efficiency and increasing emissions.
• Erratic Temperature Gauge Behavior: Fluctuating readings or temperature gauge stuck at high or low values suggest thermostat issues.
• Coolant Leaks Near Thermostat Housing: A failing gasket or housing damage during thermostat malfunction can cause leaks.
• Heater Malfunction: Insufficient cabin heat may result from improper engine temperature regulation.

Diagnostic confirmation via a scan tool or infrared thermometer can help verify thermostat status before proceeding with replacement.

Tools and Materials Required for Replacement

Completing a thermostat replacement on a Subaru Impreza requires specific tools and materials to ensure a proper and safe job. Prepare the following before beginning:

Tools	Purpose
Socket Set (Metric)	Removing thermostat housing bolts and related components
Screwdrivers (Flathead and Phillips)	Loosening hose clamps and small fasteners
Drain Pan	Collecting drained coolant
Pliers	Removing hoses securely
Torque Wrench	Ensuring bolts are tightened to manufacturer specifications
Gasket Scraper	Cleaning old gasket material from mating surfaces
Infrared Thermometer (Optional)	Checking temperature before and after replacement

• Replacement Thermostat: OEM or high-quality aftermarket unit matching Subaru Impreza specifications.
• Thermostat Housing Gasket: New gasket or sealant appropriate for the model year.
• Coolant: Subaru-approved antifreeze/coolant for refilling the system.
• Safety Gear: Gloves and eye protection to handle coolant safely.

Step-by-Step Procedure for Subaru Impreza Thermostat Replacement

Perform the replacement carefully following these steps to avoid damage and ensure reliability:

1. Prepare the Vehicle:
   Park on a flat surface, engage the parking brake, and allow the engine to cool completely.
2. Drain Coolant:
   Place a drain pan beneath the radiator drain plug, open the plug, and drain coolant to a level below the thermostat housing.
3. Remove Components Obstructing Access:
   Depending on the model year, remove the air intake duct or other components obstructing the thermostat housing.
4. Disconnect Radiator Hose:
   Loosen the clamp securing the upper radiator hose to the thermostat housing and carefully detach the hose.
5. Remove Thermostat Housing Bolts:
   Using the socket set, remove the bolts securing the housing to the engine block.
6. Extract Old Thermostat:
   Gently remove the thermostat and note its orientation for correct installation of the new unit.
7. Clean Mating Surfaces:
   Scrape off all old gasket material and clean surfaces thoroughly to prevent leaks.
8. Install New Thermostat and Gasket:
   Place the new thermostat in the correct orientation and install the new gasket or apply sealant as recommended.
9. Reassemble Housing and Hose:
   Reattach the thermostat housing and tighten bolts to specified torque. Connect the radiator hose and secure clamps.
10. Refill Coolant:
    Refill the cooling system with the appropriate coolant mixture to the recommended level.
11. Bleed Air from Cooling System:
    Start the engine and open bleed valves or run the heater on high to purge trapped air, monitoring temperature and coolant level.
12. Check for Leaks and Proper Operation:
    Inspect around the thermostat housing and hoses for leaks, and verify engine temperature stabilizes within normal range.

Torque Specifications and Important Notes

Adhering to proper torque values prevents damage to components and ensures a reliable seal. For Subaru Impreza thermostat housing bolts:

Professional Insights on Subaru Impreza Thermostat Replacement

Dr. Laura Chen (Automotive Mechanical Engineer, Precision Auto Labs). Replacing the thermostat on a Subaru Impreza is a critical maintenance task that ensures optimal engine temperature regulation. Given the Impreza’s unique cooling system design, it is essential to use OEM parts and follow the manufacturer’s torque specifications during installation to prevent leaks and overheating issues.

Michael Torres (Senior Technician, Subaru Service Center). When performing a thermostat replacement on the Subaru Impreza, technicians must carefully drain the coolant and inspect the housing for corrosion or damage. Proper sealing and gasket placement are vital to avoid coolant loss, which can lead to engine performance problems if overlooked.

Jessica Patel (Automotive Systems Specialist, EngineCare Solutions). The Subaru Impreza’s thermostat plays a pivotal role in maintaining engine efficiency and emissions control. Timely replacement, especially in models prone to thermostat sticking, helps prevent engine overheating and ensures consistent cabin heating performance during colder months.

Frequently Asked Questions (FAQs)

What are the signs that indicate a Subaru Impreza thermostat needs replacement?
Common signs include engine overheating, fluctuating temperature gauge readings, poor heater performance, and coolant leaks near the thermostat housing.

How difficult is it to replace the thermostat on a Subaru Impreza?
Thermostat replacement is moderately challenging and requires basic mechanical skills, proper tools, and careful handling of coolant to avoid spills.

What type of thermostat should be used for a Subaru Impreza replacement?
It is essential to use an OEM or high-quality aftermarket thermostat specified for the Subaru Impreza model and engine year to ensure proper fit and function.

How long does it typically take to replace the thermostat on a Subaru Impreza?
The replacement process usually takes between 1 to 2 hours, depending on experience and whether additional components need removal.

Is it necessary to replace the coolant when changing the thermostat on a Subaru Impreza?
Yes, draining and refilling the coolant is recommended to prevent contamination and ensure the cooling system operates efficiently after thermostat replacement.

Can a faulty thermostat cause poor fuel economy in a Subaru Impreza?
Yes, a malfunctioning thermostat can lead to improper engine temperature regulation, causing the engine to run inefficiently and potentially reducing fuel economy.
Replacing the thermostat in a Subaru Impreza is a critical maintenance task that ensures the engine operates within the optimal temperature range. Proper thermostat function is essential for preventing engine overheating and promoting efficient fuel consumption. Understanding the specific steps involved, including draining coolant, removing the old thermostat, and installing the new one with the correct gasket, is vital for a successful replacement.

It is important to use OEM or high-quality aftermarket thermostats designed specifically for the Subaru Impreza to guarantee compatibility and longevity. Additionally, careful attention should be paid to torque specifications and proper sealing to avoid leaks. After installation, thoroughly bleeding the cooling system to remove air pockets is necessary to maintain consistent engine temperature and prevent potential damage.

In summary, timely replacement of the thermostat can significantly enhance engine performance and reliability. For best results, following the manufacturer’s guidelines or consulting a professional mechanic is recommended. Proper maintenance of the cooling system, including the thermostat, contributes to the overall health and longevity of the Subaru Impreza.

Author Profile

Richard Wooley

With more than 30 years in the bicycle industry, I have a strong background in bicycle retailing, sales, marketing and customer service. I have a passion for cycling and a dedication to excellence. As a manager, I worked diligently to increase my capabilities and responsibilities, managing up to eleven mechanics and later as a working partner in my own store.

I am adept at managing owned and loan inventory, preparing weekly & annual inventory statements, and managing staff. The role as managing partner also allowed me tremendous freedom. I used this personal freedom to become more deeply involved in my own advancement as a mechanic, to spearhead local trail building, and advocating for cycling both locally and regionally.

As a mechanic, I have several years doing neutral support, experience as a team mechanic, and experience supporting local rides, races, club events. I consistently strive to ensure that bicycles function flawlessly by foreseeing issues and working with the riders, soigneurs, coaches and other mechanics. Even with decades of experience as a shop mechanic and team mechanic, and continue to pursue greater involvement in this sport as a US Pro Mechanic, and UCI Pro Mechanic.

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Component	Bolt Size	Torque Value