The service manual recommends you change it at 120,000 miles (and every 90,000 miles after) OR at 96 months (8 years) which ever comes first if you have the 4B1 engine (4 cyl) or the 6B3 (6 cyl) engine. Which is most likely what you have. The 60,000 mile coolant change is for a different engine.


Personally, I do every 100,000 miles, which I do in roughly 4 years.


Dex cool from GM is rated for 5 years 150,000 miles, So I'm not surprised to see mitsubishi says to change it 120,000 8 years

 

When I recently had the transaxle flushed at a Mit. dealer, I asked the recommended coolant change interval was for the Mit extended life coolant. The service manager said KMs were not as important as time. He said 5 years for Mit. coolant life.