Got an 03 4 cyl with 150K that overheats under hard acceleration. Pull over and temp returns to normal. Heater works intermittently. Temp gauge is at 1/2 during normal operation. Is this a thermostat or water pump? Does the water pump have a plastic impeller? Thanks in advance.

 

Might ask about the plastic impeller for this car year at the Toyotanation website in the appropriate section.

Are you needing to add more coolant to the overflow tank?

When the heater fails to heat is the temp gauge indication still at 1/2, if not where?