Welcome to AF.
100 degrees? Doesn't the low scale on the temp gauge start out at 160 degrees? The Dex-cool is only good for 5 years or 150K miles, whichever comes first so you are way overdue. Bad idea to mix green with orange Dex-cool so you need to flush the cooling system.
On draining the radiator go from underneath. Remove the plastic trim and use the tool shown in the tech procedure posted at our Tips & Maintenance. See link.
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