| 99 STS Coolant Change - Still More Questions?
Yes Cadillac fans, another exciting coolant change post for the 427th time. I thought I was in good shape since I had the water pump done a year ago when I got the car and assumed (first mistake) that my mechanic had changed the coolant since he’s an anal bastard like me and that’s why I go to him. WRONG. Had him decipher the receipt and it turns out he didn’t change the coolant. Since I don’t have a baseline I figured it was time. Read through FSM 2-3 times, torched up an Indian Tabac Tomahawk and tore in. Took off the lower splash guard and started searching for the petcock knob. From the top or bottom no joy – its just not there. Removed the air cleaner cover and bellows to the intake (PITA as always) to get more working room.. Back to FSM which clearly shows a petcock knob. Back to car. Finally conclude that the thing I’m looking at where I think the coolant comes out has a hex head on it. Eventually figure out that a 19mm socket fits it, unscrew it and SPLOOSH out comes the coolant. Leads me to believe I may not have an OEM radiator. Drain the coolant and remove the surge tank so the effort of removing the air cleaner housing is not wasted. Rinse it out with some distilled water a few times until it comes out clear, although there is still some gunk in the tank which I attribute to coolant pellets. Blew some air into the upper surge tank hose (just for the record: Dexcool tastes like CRAP) and got some more fluid out. Fired up the compressor and blew air into both the surge tank lines and got some more coolant out. Wrestled the lower (outlet) radiator hose off and put in three Barrs Leak tabs. Smashed ‘em with a hammer in a plastic bag per Sub’s recommendation and poured the dust into the hose and reattached it. Refilled with a mixture of 50% Prestone Dexcool and distilled water. Hold your flames: I bought Prestone coolant with the GM logo on it, certified to meet GM 6277M spec and mixed it with distilled water per the requirements of FSM and the radiator shroud decal. Using my coolant tester it tests out to -45* F. Reinstalled the intake bellows and air cleaner cover (still a PITA!) and refilled. Way confused as to why I can only get 4 quarts into the system. Ran it up to temperature at idle, adding as needed. Took it for a spin and adjusted – when I was done I got only ~6 quarts into a 12 quart system. So after all this I have a couple of questions:
The Barrs Leak “tablets” were about the diameter of a quarter and 5/8” thick – were they the right ones? Somehow I was expecting tablets about the size of rabbit turds.
Since I seem to have only gotten about ½ the coolant changed, how long should I go before changing again? The stuff that came out was clean. | 
If I redo the coolant change in 4-6 months (like when its warm?) should I hit it again with the other 3 tabs of Barrs Stop Leak?
got that. I rinsed the surge tank for awhile to get as much as I could out, but other than adding wash water to the tank (out of the car) and shaking it around I couldn't figure out any better way to clean it. I probably got at least half the goo.
I guess I thought that over time it could eventually build up in the radiator and begin to clog it. That was always the rap I heard on every other radiator stop leak. But if its worked for you on essentially the same car I'll feed it some more next time. Thanks 
