These directions are for neglected cooling systems and assume the cooling system capacity is 14 quarts. Depending on the cooling system capacity and how dirty it is, you will need...
(3) 1 gallon jugs of concentrated coolant. Preferably OEM, but I and many others have had bad luck with GM's Dex-Cool so I would recommend replacing it with either John Deere Cool-Gard II or Zerex G-05. If you want to get rid of Dex-Cool and your GM vehicle is still under warranty, you can use Mopar's G-05 (Chrysler) which has a similar color to Dex-Cool but is a superior product. It is YOUR decision to stick with Dex-Cool or not.
(15-20) 1 gallon jugs of distilled water. No matter how tempted you may be to use municipal water or well water, DON'T! Distilled water is cheap and is your friend.
(2-4) Bottles of either Prestone Super Radiator Cleaner or Zerex Radiator Super Cleaner.
You will also need dish soap, a tooth brush, a wash cloth, and a large sink or bath tub. You will also need a full tank of gas, time, and temperatures where the low will not be below freezing for a few days.
Before you start, inspect the cooling system hoses. Look for cracks, blemishes, etc. Replace the hose(s) if you find any damage.
1)Remove the radiator cap. If it is in good shape and maybe just needs to be cleaned, you can probably re-use it, but have the radiator cap pressure tested just to be safe. If the radiator cap is in bad shape, replace it with a new radiator cap.
2)Disconnect the overflow tank's hose IF THE OVERFLOW TANK IS UNPRESSURIZED and separate of the radiator. This hose is a small diameter rubber hose running from the throat of the radiator where the radiator cap goes to the overflow tank. If this is not the case then you have a PRESSURIZED overflow tank and its cap is actually the radiator cap so DO NOT disconnect its hose from the radiator as this allows you to fill the radiator. If you do disconnect the unpressurized overflow tank's hose from the radiator, put the hose in a safe place so it doesn't get caught in any belts, fans, or pulleys. Leave the hose connected to the overflow tank.
3)Disconnect the lower radiator hose to let both the radiator and the engine block drain into a bucket. I usually disconnect the lower radiator hose from just the radiator and carefully tilt the hose down while it is still connected to the engine to ensure the engine block drains. Remember the engine block will never fully drain out but what is left in it is minimal using this system of draining.
4)After the draining completes, reconnect the lower radiator hose. Be sure to not over-tighten it's clamp(s).
5)Open the bleeder valves if the cooling system has them. Refer to the vehicle's owner's manual to see if you cooling system uses them or not and where they are located.
6)Fill the radiator with distilled water.
7)Close the bleeder valves when distilled water starts coming out of them.
8)Turn the vehicle's engine on and wait for the thermostat to open.
9)When the thermostat opens, the level of distilled water will go down so add more distilled water to the radiator until it is full again.
10)Put the radiator cap back on.
11)Run the engine for 15-30 minutes at normal operating temperature with the heater on its hottest setting and its fan speed on the highest setting. Keep an eye on the temperature gauge while doing this. If it starts to over-heat then turn the engine off, allow it to cool down, and add more distilled water to the radiator then start this step again.
12)Turn the engine off and wait for everything to cool down enough to safely touch.
13)Repeat Steps 1-12 until the drained distilled water comes out clear and pretty much odor-free. This usually takes 3 or 4 more times.
14)Reconnect the lower radiator hose.
15)Open the bleeder valves if the cooling system has them.
16)Shake then pour in 2 bottles of either Prestone Super Radiator Cleaner or Zerex Radiator Super Cleaner.
17)Top off the radiator with distilled water.
18)Close the bleeder valves when distilled water starts coming out of them.
19)Turn the vehicle's engine on and wait for the thermostat to open.
20)Add more distilled water to the radiator until it is full.
21)Put the radiator cap back on.
22)Turn the engine off.
23)If you disconnected the unpressurized overflow tank's hose in Step 1, remove the overflow tank's cap and flush the coolant out of the overflow tank using distilled water. You can either work the overflow tank's hose down so it goes towards the bucket and let it it slow drain itself. Repeat until you get all the coolant out of the overflow tank. Or, you can remove the overflow tank (leave the hose on it), drain it, fill it a little pass half full with distilled water, and swish the distilled water around until you get all the old coolant out of it. Be sure to let some of the distilled water drain out through the overflow tank's hose to help clean the hose out. Reinstall the overflow tank when finished.
24)Reconnect the overflow tank hose back to the radiator.
25)Fill the overflow tank to the HOT mark with distilled water then put the overflow tank's cap back on.
26)Drive the vehicle for a total of 4-6 hours. This can be on and off but should be done within 2-3 days. Also do this when the outside temperature is well above freezing. Water expands when it freezes and can destroy the cooling system and the engine if the outside temperature gets cold enough. It is preferred to drive the vehicle with the heater on its hottest setting and its fan speed on the highest setting so the cleaner can attempt to clean out the heater core.
27)After the 4-6 hour time frame has been reached, repeat Steps 1-12 at least 3-5 times to make sure all the cleaner has been removed.
28)If the cooling system is still somewhat dirty, repeat Steps 14-27 one more time. Short of replacement, the cooling system will be as clean as it ever is going to get through chemical cleaning means.
29)Remove the empty overflow tank. Leave the hose connected to the overflow tank.
30)Using a bath tub or large sink, remove the overflow tank's cap and add some dish soap to the overflow tank. Using HOT water, fill the overflow tank a little past half full and swish the HOT soapy water around. Let some of this drain out through the overflow tank's hose to help clean the hose out as you do this. Then drain what is left out of the overflow tank's opening. Repeat this until the water drains out clear and has no soap in it. Keep doing this until the overflow tank is nice and clean inside and out. Be sure to clean the overflow tank's cap as well using soapy water, a toothbrush, and a wash cloth as needed along with the radiator cap if it can be re-used.
31)While you have the overflow tank in the bath tub or large sink, fill the overflow tank a little past half full with distilled water. Swish the distilled water around letting some of it drain out through the hose. Repeat this a few more times. Rinse the overflow tank's cap and the radiator cap with distilled water as well.
32)Reinstall the overflow tank back into the vehicle. Go ahead and reconnect the overflow tank's hose back to the radiator.
33)Reconnect the lower radiator hose.
34)Open the bleeder valves if the cooling system has them.
35)Fill the radiator with concentrated coolant. If you have a 14 quart system, you will need 1.75 full jugs (which is 7 quarts) of concentrated coolant to achieve a ratio of 50 coolant to 50 distilled water. 2 full jugs will get this closer to a ratio of 55 coolant to 45 distilled water which is preferred. Do not go past 65 coolant to 35 distilled water.
36)Close the bleeder valves when distilled water or coolant starts coming out of them.
37)Turn the vehicle's engine on and wait for the thermostat to open.
38)Add more coolant if you were unable to achieve the desired ratio of coolant to distilled water. If you have already added enough coolant, fill the remainder with distilled water until full.
39)Put radiator cap back on.
40)Run engine for 15-30 minutes at normal operating temperature with the heater on its hottest setting and its fan speed on the highest setting. Keep an eye on the temperature gauge while doing this.
41)Turn the engine off and wait for everything to cool down enough to safely touch.
42)Remove the radiator cap to verify the radiator is full of coolant. If needed, fill the radiator with concentrated coolant if you were unable to achieve the desired ratio of coolant to distilled water or with distilled water if you have achieved the desired coolant to water ratio.
43)Fill the overflow tank to its HOT mark with concentrated coolant if you were unable to achieve the desired ratio of coolant to distilled water or with distilled water if you have achieved the desired coolant to water ratio.
44)Now would be a great time to make a couple of jugs of pre-mixed coolant for future top offs. Get an empty coolant jug. Most have a window on the side of them where you can view the amount of liquid in them. They are usually marked 1, 2, 3, and 4 to show quarts. Fill the empty coolant jug with concentrated coolant from a new jug up to the 2 mark. The jug you just opened should also be on the 2 mark. Fill both jugs with distilled water up to where an imaginary 3.75 mark would be. This should give you a pre-mix of about 55 coolant to 45 distilled water. Put the caps on the jugs and shake them to mix the coolant and distilled water. With a marker, write PRE-MIX and the DATE on the jugs.
45)Keep an eye on the coolant levels in BOTH the overflow tank and radiator over the next few days. Check both of them twice a day as there may be a little bit of air in the cooling system and it will burp the air out which will lower the coolant levels. Top the radiator off and fill the overflow tank to the HOT mark with the pre-mixed coolant you made as needed.
46)Get into the habit of checking BOTH the overflow tank and radiator at least once a week thereafter.
47)Keep one of your pre-mixed jugs of coolant in the vehicle. You just never know when you may need it. If you need to top off and don't have it with you, either buy a pre-mix of the coolant that you used if you can or use distilled water.
48)If any leaks develop, get them fixed!
49)Once every year or two years, use the steps in the SECOND post in this thread and you shouldn't need to do a full blown cleaning again unless the cooling system is dirty or becomes contaminated.