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Lexus RX: How to Replace Thermostat

The thermostat regulates when coolant flows through the radiator. If there's enough coolant but the Lexus RX still overheats, a leaky thermostat might be the issue.

By Anthony Alaniz - December 17, 2014

This article applies to the Lexus RX (2007-2014).

An overheating engine can be one of the most damaging conditions a car will experience. When the engine runs too hot, the seals and gaskets around key components can warp and fail, leading to the failure of other critical components. A faulty thermostat can force the engine to overheat by preventing coolant from flowing through the radiator. Fixing and replacing a faulty one is easy and will save a considerable amount of time and money compared to leaving the job to a mechanic.

Materials Needed

  • Ratchet
  • 13-inch extension
  • 8-inch extension
  • Cheater bar
  • Various hand tools
  • Coolant

Step 1 - Remove serpentine belt and various engine covers

In order to reach the thermostat on the Lexus RX, remove the serpentine belt first. After the belt is removed, remove the necessary plastic covers the reach thermostat, which are identifiable by following the radiator pipe that goes into the engine.

(Related Article: How to Replace Serpentine Belt - ClubLexus.com

Figure 1. Rotate the bolt on this tensioner counter-clockwise to relieve it and remove the belt.

Pro Tip

To best remove the belt, remove the front tire. This makes it easier than going through the engine compartment.

Step 2 - Locate thermostat

Most thermostats are located where the radiator hose goes into the engine. The RX isn't any different. Follow the upper radiator hose to the engine block. That hose connects to the engine's water inlet. In that pipe is the thermostat. In order to remove the thermostat, that pipe will have to come out.

Figure 2. Thermostat location on the RX.

Step 3 - Place bucket under where you're working

Removing a thermostat or radiator hose will cause a lot of coolant to be spilled. Place a bucket underneath the connectors to minimize the mess.

Step 4 - Remove the number 2 idler pulley

There's an idler pulley located underneath the water inlet. You'll need to remove this pulley in order to remove the water inlet, otherwise it'll block access to the bolts securing the inlet. Wedge a screwdriver or something similar between the pulley and the engine or water inlet to keep the pulley from spinning. Unbolt it with a long socket wrench.

Figure 3. Location of idler pulley.

Step 5 - Remove water inlet

The upper radiator hose will likely be strapped to the water inlet via a clamp. Take a flat-head screw driver and loosen the clamp. Once the clamp is loosened, pull the hose off the water inlet. This will reveal the two bolts holding the thermostat in place. Remove these bolts and pull off the water inlet to expose the thermostat.

Figure 4. Unscrew these bolts to remove the water inlet.

Step 6 - Remove thermostat bolts

Remove the thermostat and be sure to remove the gaskets as well. The new thermostat will come with new gaskets. Clean the gasket seats, too, while making sure no rubber crumbles off or gets dropped into the engine.

Pro Tip

If pieces of the old gasket remain, scrape them off. Make sure no particles fall into the engine. This could cause damage to the cooling system.

Step 7 - Replace thermostat

Once the thermostat seat is cleaned, replace the new thermostat and gasket, securing it with the bolts originally removed.

Figure 5. Old, leaky Lexus RX 300/330 thermostat that needs replacing.

Step 8 - Replace hose/clamp/fluid, and clean up

Once the thermostat has been replaced, re-install the water inlet. Slip the radiator hose back onto the inlet and secure the clamp as it was before you started. Once secure, take the fluid that spilt into the recovery bucket and add it back to the radiator. Be sure to mop up any spilt fluid as it can be deadly to small children and animals. Properly dispose of any rags used during this project.

Featured Video: How to Replace Thermostat in Lexus RX

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