Ahhh, the good ole Radiator flush and fill! This should be a regular maintenance item for all of your vehicles, it will keep the cooling system up and running for years to come. I know that most manufacturers are now recommending 5 year 100k miles on this service, but I like to do it every 50k on mine. I’ve done the Envoy 4 times now and the only issue that I’ve had with the cooling system is with the thermostat. I guess maintenance doesn’t prevent everything.
This is an easy procedure on the Envoy, a little messy, but easy. You will need a catch can to catch the radiator fluid that will come pouring out of the radiator, you will need a pair of Channel locks (or some other device that can pinch the clamp on the bottom of the radiator), 3 gallons of distilled water, and some anti freeze.
First, remove the radiator cap.
Then you will need to squeeze the clamp on the bottom of the radiator to loosen it. It will open fully and lock that way but it is a pain to get unlocked. Slide the clamp off the neck of the radiator and release.
You should then be able to remove the bottom radiator hose.
Let all the anti-freeze drain out. There is no drain plug so this is how you do it. When you first remove the hose the fluid drains all over the place and it is almost impossible to catch it all. Do the best you can.
Once all the fluid is drained out, replace the lower radiator hose.
Fill the system with the distilled water. This is important! Use distilled water so that you don’t have chemicals in the system that are not expected. Some tap water will have chemicals that will interfere with the anti-freeze solution and make it less effective. This can also damage the cooling system. USE DISTILLED WATER!
When the system is filled, start the car and let it warm up. Once it is up to operating temperature, the thermostat will open and any fluid that was in the block will mix with the distilled water. You will never get it all out, but you can get most of it!
Once you see that the radiator now has a green tint (or whatever color anti-freeze you use tint) to it, you can shut the car off.
Drain the system again, be extra careful this time since the coolant will now be hot. Remember, this Envoy drains very quickly and all over the place, be prepared! Maybe even wait for it to cool down a bit….
Once all the coolant is drained out, replace the lower radiator hose and make sure that the clamp is on tightly.
Mix the anti-freeze. Use one of the empty gallons of distilled water and fill it half way with anti-freeze. Then open the leftover distilled water gallon and fill them both up. You will now have 2 gallons of 50/50 mix that is perfect for any car. (Unless of course you live in an extreme environment, then follow the recommendations.)
Fill the system up with the 50/50 mix and start the car. Let it get to operating temperature and keep filling up the radiator as the air gets burped out. Once all the air is burped out, put the cap on and make sure the overflow is filled properly.