Change coolant from the green to the extended...

I took mine to a local Cummins Coach Care shop and had them do a drain, flush and refill with Fleetguard ES Compleat OAT coolant, similar to Final Charge.

If you elect to DIY, it is not difficult but time consuming to do it right. You need to know the total coolant capacity of your coach and not just the capacity of the engine and radiator. You will need a lot of distilled water for your final flush before you start adding new coolant.