Is it critical to change coolant at 100K?

[RMcG]

Originally Posted by 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.
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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).

If I do decide to run distilled water through the system, how long should I let the system run in order to mix & help get the older coolant out of the system? Ten minutes? 20 minutes? Until the engine is hot?

(I know that there is the potential problem of diluting the coolant, since you cannot get all the distilled water rinse out of the system before you add the new coolant.)

Thanks,

R.