[rheavn]

Reread link #1 in posting #13.  It will answer ALL of your questions.  Pay close attention to the Maintenance section, subsection "Coolant Maintenance Intervals".  It will give you the mileage & time recommendations for whatever coolant type you select.  Also under the "Summary of Coolant Recommendations", pay close attention to #12 which discusses "coolant life".  Please note that Detroit Diesel also recommends "if topping off is needed, add coolant identical to the initial fill coolant.

Link #2 shows what products meet Detroit Diesel specifications & which ones are not recommended.

In reviewing "Newell Coach Annual Service and Preventative Maintenance Checklist(PM)" it lists the following recommendation:  "every 5 years flush and change coolant (if vehicle has extended type coolant).