I have a 1999 American Dream with a Cummins ISC8.3 diesel engine. It requires SCA type coolant. I've seen postings that indicate there are ELC (extended life) coolants that don't need to be tested as often as the standard types. Is a thorough flushing of the cooling system required to change from one to the other? And in general, what is the procedure to do a coolant change/system flush on an engine like this?