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Replacement Procedures for a 2001 Avalon Thermostat

by Kyle Sanstrom

A faulty thermostat can cause a number of problems, such as engine overheating and reduced cooling system efficiency. Although the thermostat is a small, inexpensive component, it’s absolutely critical to the proper operation of a liquid-cooled engine. The 3.0-liter engine in a 2001 Toyota Avalon contains a thermostat that’s designed to open at a temperature of 176 to 183 degrees Fahrenheit. The most common thermostat fault is a failure to open. In this situation, the thermostat valve doesn’t open when it should, preventing coolant from properly circulating and causing the engine to overheat.


Step 1

Allow the engine to cool for at least two hours to prevent burns and other injuries related to the high temperate of the engine and engine coolant.

Step 2

Raise the vehicle with a jack and support it with jack stands. Remove the radiator cap and place a drain pan underneath the radiator. Loosen the drain valve with a ratchet and metric socket. Allow the coolant to drain out until the stream flowing from the radiator slows to a drip. This may take 30 minutes or more. Close the radiator drain valve. Place the drain pan under the engine, beneath the thermostat housing.

Step 3

Remove the bolts holding the V-bank cover in place at the top of the engine with a 5 mm hex wrench. Remove the bolts holding the air cleaner hose and resonator in place with a ratchet and metric socket. Then remove the air cleaner assembly from the vehicle.

Step 4

Squeeze the spring clamps holding the heater hoses to the water inlet with a pair of pliers and slide them down the water hoses. Pull the heater hoses off of the water inlet.

Step 5

Disconnect the coolant temperature sensor’s electrical connector. Remove the nut holding the wire protector to the water inlet with a ratchet and metric socket and remove the protector from the inlet.

Step 6

Remove the bolts holding the water inlet pipe to the water inlet with a ratchet and metric socket. Remove the water inlet pipe from the water inlet.

Remove the nuts holding the water inlet to the cylinder head, then remove the water inlet from the cylinder head. Remove the thermostat from the inlet.


Step 1

Install a new gasket onto the new thermostat. Set the water pump inside the cylinder head opening so that the small jiggle valve on top of the in line with the top-center water inlet valve mounting stud.

Step 2

Set the water inlet valve onto the cylinder head so the cylinder head studs pass through the holes in the water inlet. Install the water inlet nuts and tighten them to 69 inch-pounds with a torque wrench.

Step 3

Remove the old O-ring from the water inlet pipe. Install a new O-ring on the water inlet pipe and coat it with soapy water. Install the water inlet pipe into the water inlet, then install the water inlet pipe mounting bolt into the cylinder head and torque it to 14 foot-pounds with a torque wrench.

Step 4

Set the engine wire protector into position and reinstall its retaining nut with a ratchet and metric socket. Reconnect the coolant temperature sensor’s electrical connector.

Step 5

Connect both heater hoses to the water inlet. Squeeze the spring clamps with a pair of pliers and slide them down the hoses and release the pliers when they are in their original position.

Step 6

Set the air cleaner and resonator assembly into position and reinstall its retaining bolts. Set the V-bank cover into position and reinstall its retaining bolts with a 5 mm hex wrench.

Fill the radiator with a 50/50 mixture of Toyota Long Life Coolant and distilled water until it reaches the top. Replace the radiator cap and fill the coolant reservoir with the same mixture until it reaches the “FULL” mark. Start the engine and allow it to come up to operating temperature. Check for coolant leaks and then re-check the coolant level. Add coolant if necessary to raise the coolant level to the “FULL” mark on the side of the coolant reservoir.


  • Removing the engine block drain plugs to drain coolant is not necessary for this procedure. Because the thermostat level is much higher than the block drain plugs, the coolant will safely drain to a serviceable level for the thermostat replacement procedure by using only the drain valve in the radiator.


  • Engine coolant is very toxic if ingested, especially for animals and small children. Take caution when working with coolant and make sure any spills are promptly cleaned up.

Items you will need

  • Jack
  • Jack stands
  • Drain pan
  • 5 mm hex wrench
  • Ratchet set
  • Metric socket set
  • Pliers
  • Toyota long life engine coolant
  • Distilled water

About the Author

Kyle Sanstrom has been writing professionally since 2008. His articles have been published on several websites including eHow and Automobile Insight. Sanstrom has undergone advanced automotive training at the Dunwoody College of Technology, holds an Associate of Arts in general studies from Century College and has more than 10 years of experience in all aspects of automotive repair and diagnosis.

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