To save the coolant. Plus, if you don't drain it, you'll make a big mess when you pop the cover off.

i agree don't drain the coolant it will only lose about 1/2 of a gallon. I just did mine the inner gasket had broken and was lodged in the opening keeping it partly open
http://img208.imageshack.us/img208/5...stat007.th.jpg
http://img232.imageshack.us/img232/5...stat006.th.jpg

There are right ways, and wrong ways of doing things. To not drain the coolant properly is definitely the wrong way. Losing a half gallon on coolant on the ground and all over the engine (to smell for the next day or two of driving) is a sign of mechanical incompetance, to say nothing of a total disregard for environmental issues.

Here puppy, lick this mess up.

Jeesh.

Mine just did this this morning. Already had an appointment to get the oil changed before the Tail if the Dragon cruise. Called and told them to look at this too. On the way home from work however the temp gauge and dic started to register again. Must have came unstuck. Still going to have them fix it. I might as well get everything I can out of my 100,000 mile warranty

I changed mine yesterday,cleared the code at Advance Auto, $183 saved!

I just did mine yesterday at 73K+. It had thrown a code for not getting up temp properly, and having read about this earlier, I went right for it. My old one was just like max69power's above - the inner gasket was stuck in the valve, so it never completely closed.

Access is not good on the SS, and it took me a couple of hours, which I mostly spent trying to find a dropped bolt and a dropped 10mm socket on different occasions. I accessed the upper bolt from above and the lower one from below the car, and that seemed to be pretty straight-forward. After refilling, I had a bit of a bubble in there and it almost overheated at first, but after leaving it to cool for a couple of hours it had pulled in all the coolant from the reservoir. I did that cycle one more time, and all seems well now. The CEL is off, engine temps are normal, I have heat, etc. My total bill was around $50.

Tip: to clear that code, you can disconnect the battery for a few minutes (and it won't affect the radio settings etc.), OR just drive it a few times and the code will clear after a few drive cycles. :)

Just changed out the thermostat on the kids' HHR this morning after sporadically getting the P0128 code over the last several weeks. Thanks to you guys, it was real easy, even for a software engineer!

So, why do you have to drain the coolant? I changed my thermostat a while ago and I didn't drain the radiator as described and only lost a cup full. Is it just an environmental thing or a mechanical thing? Curious because I have to do it again tomorrow!

It's just good practice, however Dexcool is good for150,000 miles. But for the environment, you should "capture and dispose" of the leakage.