The last time I flushed the cooling system I was in a hurry and only drained the radiator and refilled. This time, I want to drain the whole system and flush with fresh water. I need to run it long enough to get the thermostat to open so I can get a complete fluid drain. How do I know when the thermostat is open after starting the engine?

 

Sorry that I do not have a direct answer for your question. However, I hope that the following information is helpful.

During the coolant flushing process I got the bright idea of temporarily removing the thermostat. It is very easy. I completed three iterations of distilled water flushes with the thermostat removed. For sure I let the engine warm-up to operating temp during the flush. Sometime during the process, I observed the check engine light was on.

After completing the flush, I reinstalled the original thermostat, rad replacement and completed other maintenance items, I refilled the cooling system and fired-up the car. After running the car for a period of time, the check engine light remained on. I cleared it with my scan tool. I road tested the car and all is good.

Just note that if you get the idea of removing the thermostat during a coolant flush, be sure to have a scan tool available.

 

You'll know when the upper rad hose gets hot.

 

City water may not be good for your cooling system. If you have hard water, it will leave deposits on hot surfaces. Get all the city water out and then fill with purchased 50/50 coolant or use 100% coolant plus DISTILLED water.
I ruined one of my cars with city water!
Ken

 

As Michael A mentioned you will know when the upper radiator hose gets hot. When I change the coolant on my GM cars I drain the coolant and refill with clear drinking water from the tap, run the engine without the cap on the system and wait for a few minutes after the hose gets warm before turning off the engine and draining the system again. I repeat this process several times until the drained fluid looks clear and I can't see any orange color evident.

Once the fluid is clear I close the petcock again and add the proper amount of Dexcool to obtain a 40% coolant to 60% water ratio and top off with water. Then with the cap off I run the engine until the thermostat opens and rev the engine to about 2K rpm to burp air out of the system. So far this has gotten all of the air out of all my GM vehicle's cooling systems for the last 25 years so I haven't had to vacuum bleed them.

I have lived in areas where the water was extremely hard (upstate NY) and have never had an issue with using drinkable tap water in the cooling system of my cars. GM doesn't recommend distilled water and I don't use it. I have owned my 2003 Tahoe since December 2002 and have changed the coolant every 5 years since then. The cooling system is still working fine and all parts of it are original to the vehicle including the hoses.

Bill

 

Thank you, one and all for your help. Have a good Labor Day holiday.

 

One more question. After pouring water through the cooling system until it's clear, you may have about 20 quarts or more of fluid. How are you folks disposing of all that contaminated water?

 

The Firestone Complete Auto Care business near me accepts coolant to recycle. Call around to your local shops and see if they take it.

 

Thanks. I'll check around here.

 

Check your city. Around here you just dump it in a drain, the treatment plant handles it.