Is it critical to change coolant at 100K?

[johnwk]

It wouldn't hurt to run a few gallons of distilled water through the system (following the same drain-fill-drive-drain procedure) before filling it with the new coolant.

I'm neither an expert nor a perfectionist, but I just used the Toyota-labeled Prestone stuff from the auto parts store.

A mini-tip: I found that only unscrewing the radiator drain plug part of the way prevented it from spraying all over the plastic under-engine guard (where it will collect and sit).

A word of encouragement for anyone considering doing this for the first time: changing my coolant following tmontague's instructions in another post was the first real job I ever did on any car ("real job" = something I would have normally paid someone else to do), and it really helped me to get over my fear of DIY maintenance.