I've watched some You Tubes of people not removing drain plugs from the engine block, but just pulling coolant hoses and flushing and back flushing with a garden hose. Granted, these are all done on cars that aren't my car's LS1 engine. I'd rather not pull the engine plugs if possible. 20 year old threaded screws, bolts, and nuts tend to give me trouble by stripping, snapping off at the head etc. Does anyone else flush and back flush without unbolting the engine drain plugs?

 

I did this and replaced my radiator last year to my 2000 WS6. Figure the block waterpump heater hoses and core will hold about 1 1/2 gallons. Replace an equal amount of straight antifreeze not a 50/50 mix! It should be topped but run for a distance let cool and check overflow and level in radiator.

 

i wouldnt bother , drain from the petcock on the radiaor bottom and get yourself a funnel like this , it making air bubbles a thing of the past .

 

Once you get the system clean, I would recommend regular drain/refill intervals (I do this every two years). This only gets rid of about 1/3rd of the coolant, but no need to worry about an entire complicated flush process if you frequently refresh the system - unless maybe you drive a lot of miles. I haven't 'flushed' mine in nearly 20 years since getting on this process, no problems so far and the radiator always looks clean on the inside (but this is for my limited use vehicles, so not much mileage between changes).

 

^^^ Once I had the Dexcool removed many years ago with the universal green stuff,, I also have done this method. Everything looks clean with zero issues. 80,000 miles on the Trans Am now.
I also used this method with my old 2007 Mustang GT. I never flushed the system and used the recommended Ford coolant each time at the 2 year mark.. We travelled all over the US and never had a coolant related problem. Just sold the car last month with 65k miles on it.
This method of always adding the 'fresh' with the old every few years keeps the system working fine.