Since brand new, I have changed the coolant in my 14 year old Avalon every two years using only Toyota Red coolant with distilled water. Recommended change interval is 2 years or 24k miles. This worked well since I used to drive 10-12k miles per year. Now I only drive about 6k miles per year. Can I extend the coolant change interval to, say, every 3 years without causing corrosion in the cooling system? Thanks.