I recently had a mechanic replace a leaky water pump on my 1999 GMC Jimmy w/ 72,000 miles. At the time he replaced it he flushed out the system and switched from the factory Dextron coolant to the green type antifreeze. He claimed it would prevent rust better than the Dextron.

Did I get taken for a ride? Is switching coolants a good idea? Should I be concerned or aware of anything in particular?

Thanks for any help!