Just another preaching to the choir here about only using OEM Toyota for the thermostat. My 86 started running hot (3/4 up the gauge, not the end of the world but higher than it should be running) once the ambient temperature got towards or past 100 degrees outside. Not knowing the age of the coolant or what thermostat was in it, I did a patented ChrisFix super flush (lol), replaced the fan shroud (old one wasn't properly seated against the radiator all the way around, plus the ears had snapped off) and pulled the old thermostat.

The thermostat was obviously very old, the part number I pulled off came back as a Robert Shaw branded thermostat. They apparently still make home thermostats, I have no idea if they still make ones for cars though, this particular one had no jiggle valve and was just closed all the way around. It was likely in there since the first Bush was president so it wasn't terrible but was in desperate need of replacing.

Anyways, I just got back from running some errands and the needle has yet to go past 1/4 of the way up the gauge! I'll put some miles on it in traffic and 105 outside just to be sure but it's amazing how much of a change these little thermostats have on our vans.