Does anyone know the logic/engineering reason behind manufacturers recommending one service interval for the factory coolant and then roughly half that for subsequent intervals?
For example, my Toyota manual states: “Initial engine coolant replacement at 100,000 miles/120 months. Replace every 50,000 miles/60 months thereafter.”
My Subaru was similar. The manual states: “Subaru Super Coolant. 1st replacement interval is 11years/137,500 miles (220,000 km). 2nd replacement interval is 6 years/ 75,000 miles (120,000 km) after the 1st.”
What gives?
For example, my Toyota manual states: “Initial engine coolant replacement at 100,000 miles/120 months. Replace every 50,000 miles/60 months thereafter.”
My Subaru was similar. The manual states: “Subaru Super Coolant. 1st replacement interval is 11years/137,500 miles (220,000 km). 2nd replacement interval is 6 years/ 75,000 miles (120,000 km) after the 1st.”
What gives?