Thanks a lot, you guys are excellent. I have checked the service spec for 5S-FE engine and see this:
Valve opening temperature: 80 – 84°C (176 – 183°F)
Valve lift at 95°C (203°F) 8 mm (0.31 in.) or more
I googled for how thermostat work and found this http://auto.howstuffworks.com/question248.htm
My understanding is that the thermostat valve will close until engine reach 176-183 then it will open to let coolant run to radiator to cool down, at this point, the radiator fan will also start to work, is it correct?
Can someone explain what does it mean "Valve lift at 203°F"?
Must I use a laser thermometer to measure engine temp, how? Can I use a normal electronic thermometer?
If I'm to replaced the thermostat, should I use a normal thermostat or a bypass thermostat for the 5S-FE engine. This is not mentioned in the manual.