Read this about your problem.
http://www.4crawler.com/4x4/CheapTricks/index.shtml#ThermostatTSB: 029032787 22R-E Engine Temperature Overshoot
It says:
Some 1984 pickup trucks and 1983-1984 Celica models, equipped with 22R-E engines, may experience a condition called "temperature gauge overshoot". After starting a cold engine the temperature gauge will indicate a higher than normal engine temperature for a short time just prior to the thermostat opening. After the thermostat opens, the temperature gauge will return to the normal range. A new double valve thermostat has been made available to reduce temperature gauge overshoot.
And calls for part number 90916-03070 which according to the TSB replaces 90916-03055.
