Nevertheless, why are you wanting to replace the thermostat? Has the coolant been changed as recommended or was it neglected?
I am considering replacing the thermostat because the car is taking about twice as long to start blowing really hot air out of the vents than it did in the past. It's a longer, slower.build up to serious heat, which is problematic for keeping the windshield clear in the winter. I have changed the coolant every five years.
Also, when the car is finally fully warmed up, while the heat output is good, the temperature at the vents drops slightly when stopped at a traffic light vs while the car is underway.
This car is just behind yours in mileage at 235,000. I believe this is the original thermostat. Another owner put the first 80,000 miles on the car - their records showed they kept up with regular maintenance, but no thermostat replacement.
I was going to replace the thermostat, water pump, upper and lower radiator hoses, and while I was at it, have the local electric shop.rebuild the alternator. No problems with the alternator now, that would just be preventative maintenance. I will pick up the Toyota thermostat.