I generally change-out coolant at 3 years irrespective of what version I use. The longer coolant stays in the engine, the more acidic. Coolant test strips are available to measure the coolant pH . It usually starts out in the 7.5-8.0 range when newly installed, then decreases. Below 7, that means it has become acidic. Best to change it out at that point. I wouldn’t allow it in any of my engines lower than 6.5.