How to Replace a Thermostat in a Toyota Siennaby Russell Wood
The thermostat on a Toyota Sienna is similar to a bodyguard at a nightclub. They both control the flow of things going in and out of the place they're guarding, which with the Sienna is the engine. If the thermostat goes out, then the engine won't cool properly, and could overheat, causing damage to the engine. In this case, the project vehicle is a 2005 Toyota Sienna, but the process is similar for other vehicles as well.
Allow the vehicle to cool for 2 to 5 hours prior to working on the radiator so that you don't burn yourself. Place the drain pan underneath the radiator and open the petcock at the base of the radiator to allow it to drain. Once it stops draining, tighten the petcock.
Unplug the engine coolant temperature sensors on the thermostat housing, which is in the center of the engine block, at the front by the radiator. Then unbolt the water inlet pipe from the water inlet on the engine block and pull it away from the block.
Unbolt the water inlet from the engine block using the 3/8-inch ratchet and socket. Pull it away and pull out the thermostat with it, as well as the thermostat gasket.
Set the replacement thermostat gasket, then the thermostat in the housing. There is a small valve on the thermostat called a jiggle valve. This must be pointing up toward the stud at the top of the water inlet to function correctly. Reinstall the water inlet using the ratchet.
Install a replacement O-ring--included with the thermostat kit--onto the water inlet pipe, then bolt the pipe to the water inlet using the ratchet.
Open the radiator cap and fill the radiator with the Toyota coolant. Once it's full, reinstall the cap.
Things You'll Need
- Drain pan
- Toyota coolant
- Flat-head screwdriver
- Replacement thermostat kit
- 3/8-inch ratchet and socket set
- Never work on a hot engine with hot coolant, as you risk burning yourself.
Russell Wood is a writer and photographer who attended Arizona State University. He has been building custom cars and trucks since 1994, including several cover vehicles. In 2000 Wood started a career as a writer, and since then he has dedicated his business to writing and photographing cars and trucks, as well as helping people learn more about how vehicles work.