Originally Posted by 3ToyGuy

If it hasn't been changed since the truck came out of the factory, a flush-n-fill would be called for. If it's been changed more recently, and I sure hope it has been, a drain and fill would be quite adequate. Take a look at the fluid, if you don't have solid information an the last change out. If it's all nasty, rusty, whatever, a flush is called for. If the inside of the radiator isn't all nasty and rusty, or the water pump isn't leaking, no drips in the cab from the heater core, etc, a simple drain and fill is acceptable.

Also, you might want to check the water hoses for softness, swelling, cracks, etc. Once again, if you have no information on the last change, it can't hurt to put new ones on. The OEM hose clamps are actually the preferred clamps, as well. They hold better than the screw-down ones.

It will never hurt either, to put in a new thermostat. Cheap insurance against problems. Same with the hot water control valve. They're a cheap plastic, and can disintegrate when they get older. Trust me on that!

Always ensure you burp the system if you break it open, or even just drain and fill the system. These Toyotas like to hide air bubbles in little, sneaky corners.

Good luck to you!
Pat☺