If you don't want to spend a lot of money for Volvo coolant, make sure the coolant your buy is for aluminum alloy block/head engines. Do not get coolant for cast iron block engines.

The heater core is always 'open', so the heat doesn't need to be turned on to flush the system. Besides, there is only a cup of coolant in the heater core.

I always drain the system by disconnecting the bottom radiator hose at the engine. The plastic drain on the radiator can easily be broken, and that is a bummer. I will never use house water, which is quite 'hard' where I live, to clean out the rest of the coolant. You could just fill the system with a gallon of distilled water, run the engine for a minute, and then flush that.

Remember to re-clamp the hoses in the same place, if the clamp is in a new spot you could compromise the hose. And, do not over tighten!

Klaus
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Always willing to listen, just not able to take direction.