Here's a write-up that I made a while back.
Viper drain and refill cooling system for 97 GTS
Jerry Scott 4-10-01
1. Put the car on four jack stands at least 17 in. off the ground.
2. With the system cool, remove the fill cap. Open the heater temperature control to full open. Remove the plug in the radiator with an Allen wrench, by slightly tightening it first, then removing it after it breaks loose. This will drain approximately 9 quarts of the total 12.8 quart system.
3. Pull the overflow hose off the surge tank; insert a 3/8 in. o.d. clear Tygon hose into the rubber hose and siphon the coolant out of the overflow tank. I was concerned about removing the plugs in the engine block and getting a good seal, so I did not drain the block. I felt this was unnecessary.
4. Replace the plug in the radiator; fill the surge tank and radiator with 2 gallons of clean water.
5. Replace the cap and run the engine with the heater control fully open, until the thermostat opens and all the fluid is mixed.
6. Shut off the engine and after the system cools, remove the drain plug and drain again.
7. Repeat steps: 4, 5, and 6, two or three more times.
8. Replace the radiator drain plug for the last time with anti-seize compound and fill the surge tank with 7 or 8 quarts of new coolant (I used 8 quarts). I used the Mopar extended life, but I have heard that Havoline makes a very good coolant that NASCAR uses. Also add one 12 oz. bottle of Red Line Water Wetter. Fill the surge tank half full with distilled water.
9. With the filler cap still removed, squeeze the top radiator repeatedly with both hands until you get no more air bubbling out of the surge tank.
10. Put a funnel into the overflow bottle hose and fill with about 1 quart of distilled water. Top the surge tank with distilled water, put on the cap and run the engine until the system is hot.
11. Let the system cool, remove the surge tank cap, fill to the top with distilled water. Again using the funnel in the hose, fill the overflow tank with water so that it is between the two marks in the wheel opening. Reconnect the hose to the surge tank; replace the cap to the surge tank, and the procedure is completed. This was my way and I'm sure others will have their own procedure for getting this done.
