I check the overflow canister about once a week. Always right level in my 2005 4runner. Never had an overheat in 15 years.
Your radiator is definitely done.
NAPA radiator with lifetime guarantee is way to go. Get the receipt and keep it. NAPA will replace it if it ever fails.
2 gallons of coolant is enough. Zerex for Asian cars is pink. Amazon has it for $18 a gallon.
Hope you don’t have other issues. Overheats can ruin a V6 4.0.
I have same engine as you with 150,000 miles.
Thanks for the info on the NAPA radiator. That is a steal. I bought a starter with a lifetime warranty! Still have the box and the receipt. It's my third starter.
I'm on original WP (150,000 miles)
Life Expectancy of Water Pump? | Toyota Nation Forum
Toyota 4Runner Engine Water Pump. Main Engine Water Pump - 161006939883 | South Dade Toyota, Homestead FL