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How to Change a Radiator Valve

Maintaining the right operating temperature keeps your engine running efficiently and prevents damage from excessive temperatures. Once the engine coolant is hot, it’s the radiator valve, otherwise known as a thermostat, that keeps the engine temperature in the right range by regulating its flow through the rad.


Of the cooling system parts, the thermostat is the most likely component to fail. If it does, you may have problems with overheating that cost a small fortune to repair, or the engine won’t achieve its optimal temperature. When the thermostat needs to be changed, parts are usually under $100 with few exceptions, so long as additional damage hasn’t been done.

How a Radiator Valve Works

The design of a car thermostat is simple yet effective. It typically consists of a cylinder made of metal or plastic that contains a temperature-sensitive element filled with wax, a spring, and a valve.

The temperature-sensitive element contains wax that expands when it gets hot and contracts when it cools down. This movement of the wax element is transferred to the valve through the spring. When the engine is cold, the spring holds the valve closed, preventing coolant from flowing to the radiator.

As the engine warms up, the wax element expands, pushing against the spring and eventually causing the valve to open. This allows the coolant to flow through the radiator and regulate the engine temperature. That’s usually around 180 F, give or take. The thermostat also has a bypass that allows a small amount of coolant to circulate even when the valve is closed, helping to warm up the engine more quickly.

What Goes Wrong with a Thermostat?

Several things can go wrong with a thermostat or radiator valve, including: 

There are several things that can go wrong with a car thermostat:

  • Sticking open. Coolant will continually circulate through the radiator if the thermostat sticks open, causing the engine to run colder than it should. This can reduce fuel efficiency and performance and even cause you to fail a smog test.

  • Sticking closed.  Coolant would not circulate through the radiator if the thermostat sticks closed, causing the engine to overheat and leading to engine damage or other components.

  • Worn spring. Over time, the spring inside the thermostat can weaken. The thermostat can fail to open or close as needed.

  • Wax element failure. If the wax element inside the thermostat becomes damaged or leaks, it will not be able to expand and contract properly.

  • Blocked passages.  Dirt, rust, or other debris can accumulate in the passages and prevent proper coolant flow.

Steps to Change a Radiator Valve (Thermostat)

Changing a thermostat or radiator valve is usually a straightforward procedure that a novice DIYer will be comfortable taking on. Depending on the location of your engine, it can take 30 minutes or less, or it could take a few hours. You first need to locate where the thermostat is located, usually at the upper end of the engine block under the housing neck where the radiator hose connects to. Some thermostats are more complex and integrate the housing, a coolant sensor, and one or more water outlets.

From there, collect your tools. You’ll need the following:

  • A flat screwdriver
  • A ratchet and socket set
  • Radiator hose clamp pliers
  • A drain pan
  • Engine coolant
  • A new thermostat and gasket
  • Hand and eye protection

Before opening the cooling system, let the engine cool for 30 minutes to an hour. Otherwise, hot coolant or steam can escape and seriously burn you or others nearby.

1. Drain the coolant

Place your drain pan or bucket under the petcock valve on the rad. If your radiator doesn’t have a drain on it, position the bucket under the lower radiator hose. Open the valve or remove the hose from the radiator and drain the coolant.

2. Remove the thermostat housing

There may be a few parts, ducts, or engine covers that need to be moved or removed to get at the thermostat housing. Once you have access, remove the hoses with your hose clamp pliers or a screwdriver and pull the hoses free. You may need to use a flat screwdriver to work the hoses off of the outlets. Then, unbolt the thermostat housing from the engine block.

3. Replace the thermostat

With the housing removed, you should be able to see the thermostat if it’s a separate part. It’s slightly UFO-shaped with a flat ring that has a gasket on either side. Some radiator valves are integrated into the housing and are replaced as an assembly. Clean the mounting surfaces for the engine block and the thermostat housing well with the thermostat removed. Install the new part, being sure the thermostat is oriented correctly for coolant flow.

4. Re-install the thermostat housing

Install the housing with new gaskets in place, then tighten it according to the manufacturer’s spec. Sources like ALLDATA can provide the correct specification.

5. Add engine coolant

Add a 50-50 mix of distilled water and concentrated engine coolant into the radiator. Ensure the coolant you choose is the correct type for your car’s make to prevent unintended reactions.

6. Bleed the air from the cooling system

Start the engine and let it run for a few minutes, checking for leaks. Then, turn off the engine and allow it to cool. Check the coolant level and add more if necessary.

How to Maintain a Radiator Valve and Identify Problems

How can you prevent thermostat issues? The most important thing you can do is change the engine coolant according to the maintenance schedule. If the coolant isn’t strong enough or it’s become acidic, it can lead to blockages or corrosion on the thermostatic radiator valve. 

It might be too late if you have these symptoms:

  • A Check Engine light illuminated with temperature-related DTCs
  • The temperature gauge reads too high or too low during normal operating conditions
  • You’ve noticed overheating symptoms regularly without signs of a head gasket leak or water pump problem
  • You aren’t getting enough heat in the cabin on cold days

For a small, inexpensive part, the thermostat plays a huge role in keeping your engine healthy and operating efficiently. Prevent problems by performing your routine cooling system maintenance, and if you have an issue, replace your radiator valve or thermostat as soon as you can. Of course, you’ll find the parts you need at AutoZone to fit virtually any vehicle you drive.

Frequently Asked Questions

Can I change a radiator valve myself, or do I need a professional?

Usually, a thermostat or radiator valve can be changed by a DIYer with a few common tools and basic mechanical knowledge.

How do I know if my radiator valve needs to be changed?

If you notice inconsistent temperature readings, there are DTCs related to engine cooling, the engine is overheating, or the in-cabin temperature is below normal, you might need to change the thermostat.

What are the signs of a faulty radiator valve?

Typical signs of a faulty radiator valve include a Check Engine light on, poor heat in your vehicle, and the engine tends to run too cool or too warm on the gauge.

Can I use any type of valve to replace my existing one?

Thermostat valves have a range of shapes, sizes, and temperature ratings. Choose the right one for your car specifically or you could experience severe operating issues.

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