I'm sorry I totally missed the mileage of the car. Having said that, 100K anitfreeze has a bad habit of getting gunky. If its the original antifreeze in the car, it is now working on 5 years old, so yes I would say a flush is in order due to time, not miles. Heater cores have very small tubes that plug up with the gunk.
There are cleaners that wont harm engines regardless of what they are made of. We constantly use BG products on all engines that come in the shop and have never yet (knock on wood), to my knowlege, had an engine repair due to any of the chemicals involved with a power flush. I'm not plugging BG products, but that is one that I am aware of that is safe.
EDIT: The previous poster is correct in that the instructions say to not drive the vehicle with the cleaner in it. In my personal car, I drive with the cleaner in for a couple hours to ensure a thorough cleaning.
Monday, November 12th, 2018 AT 4:27 PM