I recently changed my coolant. (I didn't check the forum) I added Amsoil Coolant Boost
So my thermostat rubber seal fails within a month of adding the Coolant boost.
I go get a Stant 14078 thermostat (it was the only one they had). This was the lowest cost/grade. It was the one without a rubber seal and jiggle pin. The premium ones had the rubber seals in the picture.
I take the wheel, liner, belt, alternator off. I install the 14078 Stant.
sitting in the drive car heats up and thermostat appears to be working. I start driving and the temperature starts drops just like the bad OEM one. Cruising at highway speeds the car would drop below 150 deg F. The car wouldn't produce much heat for the cabin either.
I got the oem one from toyota. Drained all the coolant. Changed the thermosat. The car is back up and running strong again. It was low 30's yesterday and the car ran at 183deg F, a beautiful thing.
Here are a few pointers for the change.
DO NOT USE STANT 14078 THERMOSTAT!!!!!!!!!
1. Disconnect the alternator! Pull it toward the frame and set it on the frame, so you can get your arm under it.
2. You can see the thermostat housing and nuts through the side intake and from above with the alternator removed.
3. I found it easier the second time to move the alternator to get to the nuts. The top nut with arm above the alternator.
4. Alternator bolts are 12mm and 14mm.
5. Thermostat housing nuts are 10mm.
6. You have to remove either the engine access panel or the diffuser to do the work. You don't have to remove both. I left the engine access panel on (the second time).
7. There is one electrical connector I needed to unplug. The rachet head was too thick.
8. You do get better with practice.