salimshah

Tools:
10mm socket and various extensions 9"+
12 & 14 mm sockets.
Narrow zip tie.
Liquid soap.
Low range torque wrench. (in-lb and NOT ft-lb)
Allen key to undo the v-bank cover.
Magnet ... the one at the end of telescoping stick (like the antenna). Dont do this job without it.
Thermostat (please check with dealer and your vin # to confirm you are getting the right part) 90916-A3003
Gasket for thermostat 16325-62010
Oring for metal tube 96761-35031
Clean 1 gallon Jugs (qty) 2 if you plan to reuse the coolant. If has been 2-1/2 since last coolant change, you might as well do the coolant replacement.
1/4" tube of about 18" in length.

Thermostat is behind valve cover (2-4-6) and the inlet hose connects to metal tube, which is directly above the starter. The metal tube has a O ring that secures the connection to the thermostat. Thermostat is held in place by 3 nuts. Top one is visible, the bottom one is partially visible and the 3 one (towards the firewall) is not visible. All three can be reached with extension. You can feel all of them but for the the third, you have to work blindly

1. Connect the tube to the drain nipple on the engine block. The nipple I used is between the firewall and the engine roughly in line with the acc. pedal. The nipple is tucked behind a plate. Stick the other end in the collection jug.
2. Undo the shut off bolt which is at the base of the nipple. Loosen enough to get the flow going. Keep in an eye as you will have to switch jugs when the jug number fills up.
3. Make sure the key is out of ignition for about 2 minutes before undoing the - of the battery terminal. [for safety]
4. Remove the V-bank cover. "L" and 3 nuts on the front edge.
5. Disconnect the MAF sensor plug. Squeeze out the strain relief.
6. Disconnect the vac hose behind the air box.
6. Loosen the clamp that connects the air filter to the air-intake.
7. Undo the clips holding the top of the air-filter box.
8. Remove the top and air filter.
9. Remove the 3 bolts at the bottom of the air box.
10. Unhook the strain relief that holds the accelerator cable behind the air box.
11. Undo the holding clip that is holding 2 ground wires below the acc cable hook.
12. Remove the air box bottom and remember to clean it out.
13. Disconnect the temp gauge connector.
14. Clip of the wire support but do no mutilate the base. There is a slot in the base and you can use it to put a new zip tie.
15. Do not loosen the pipe and loosen the 3 nuts without trying to shake the thermostat housing. Use the long magnet to grab the nuts.The metal pipe if left in place as I advise will keep the thermostat housing in place and the nuts will not fall off.
16. Remove the bolt holding the metal pipe to the engine block. Wiggle the pipe out of the thermostat housing. Remove and discard the old Oring.
17. Extricate the thermostat housing.
18. Use pliers and twisting motion to remove the thermostat. Make sure the gasket is removed from the receiver.

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19. Put the new Gasket on the thermostat. Make sure the edge of the thermostat goes in the slot of the gasket.
20. Apply soapy water on the gasket and insert it back in the receiver.
21. Jiggle valve is a loose pin on the surface of the thermostat. Align the jiggle vale with the top stud/post. (spec is +/- 15 degrees axially from the stud). Spring portion goes down the hole.
22. Snake the thermostat housing back, on to the 3 studs.
23. Use the magnet to get the nut on the exposed top stud and gently thread to the base .. we are not trying to torque it down just yet, but expose as much of the other two studs.
24. Do the same with the 2nd nut. Then the third (blindly or with feel). Once all are faced down, torque them evenly 69- IN-LB
25. Apply soapy solution to the pipe O ring. Insert gently and fasten the holding bolt.
26. Reconnect the temp gauge.
27. Examine all hoses and connectors.
28. Install the air-filter box. Make sure you secure the ground wires and the accelerator cable properly.
29. Reconnect the vac hose at the back of the air box.
30. Reconnect the MAF seņor and snap back the strain relief.
31. Reconnect the battery.
32. Fill the radiator.
33. Look for leaks.
34. Run the engine and bleed the air out of the coolant circuit. Read up the coolant replacement DIY.
35 Once you are ensured that there is no leak, install the V-Bank cover.

Overall the job is pretty intuitive but dont attempt it without the magnet.

Salim

hypervish

Great DIY! I agree, a magnet is very helpful. I've done this job twice now on a 1MZ-FE; once on my Sienna and then the ES300.

owenstrawn

Can you really do this without removing the starter? I couldn't manage to separate the inlet tube from the water inlet in place so I had to remove the starter to get the assembly out of the way.

ukrkoz

I didn't remove starter.
BUT!!
Have starter covered from possible coolant spill.

salimshah

Neither did I.

Salim

nutjob99

thanks iam about to do this when i replace my Radiator.i broke off most of the top hose connector while leaning on it to loosen my oil filter 1 month ,hooked it back up with some JB weild and tape just to run errands its holding good but not enough to hit the HYWAY...cost ,$ 55 raditor, 40 for both hoses 25 for stat. 20 for coolant .$150 ,priceless.wish me luck.

bbambrough

Thank you so much. This is very helpful

trips1

Please can someone comment if the following thermostat part number is correct for a 2001 Lexus RX300.
90916-03129

I could not find the part number mentioned in the original message (90916-A3003). Am finding 90916-03129 on ebay and it is mentioned that it will fit 2001 Lexus RX300
https://www.ebay.com/itm/192390367976

Thanks!

LeX2K

90916-03084 is the original number which changes up to 90916-A3003. There are several other 'stats that are functionally the same with different part numbers (for example 90916-03129 as you listed) they also change up to 90916-A3003.

salimshah

Please call the Lexus parts and give them your vin to get the latest part-number. They make enough money to answer a simple question over the phone.

Salim