On my 02 Odyssey, the initial coolant change interval is 120,000 miles or 10 years, then 60,000 miles or 5 years thereafter. Can anyone tell me the reason for the shorter interval after the first change? Is it perhaps based on the assumption that, during subsequent changes, not all of the coolant will be replaced? If so, and if I elect to get a complete replacement (not just a drain and full), then why wouldn't I be safe waiting another 120,000 miles? Thanks.