Coolant Replacement: Lazy Man's Flush ?

I assume you are referring to the engine coolant system. Which of the three drain plugs are you going to open, to implement this process?

If you open the radiator drain plug, then you'll replace the radiator fluid but the engine and coolant heat recovery canister will probably retain the old coolant.

If you open the coolant canister drain plug, this will probably purge the radiator and canister fluid but the engine block will retain old coolant.

If you open the engine block drain plug, the engine block will be purged but the radiator and canister will retain old coolant.

Also how will you know when the old coolant has left the system and new coolant is starting to drain out? At $20+ per gallon, you probably don't want to waste the new coolant unnecessarily.

 

"Top" would probably be the engine drain plug.

I think that there's no need to open the radiator drain plug because if you drain via the coolant heat recovery canister plug, that will take fluid from the radiator.

You've proposed a very interesting idea, my main concern is that you'll have to guess when the old coolant is out. I'd suggest doing the canister plug first, and draining 6 quarts there. Then move to the engine block plug and take 2 quarts there. At that point I think you would be justified in declaring victory over this project.

Regarding the inverter coolant, it is not that hard to get the air out of the system, but if you want to use the same method, why not. The only issue is that the drain opening is pretty big (24 mm hex head plug) and it may be hard to drain fluid in a controlled manner. I would drain 3 quarts and then be done with that system.