GM V6 cooling systems...

Noticing that all-too-familiar growling noise emanating from under the hood of my 2007 Pontiac Grand Prix, I had that sneaking suspicion that the factory water pump had finally begun to give up the ghost after 70,000 miles. I guess that I can’t complain.

So, off to the auto parts store to get the necessary items, new pump, thermostat, serpentine belt, and two gallons of the tried and true Prestone full strength coolant, just to be sure I had enough. I figured that I should get to it before it starts getting really cold outside. Didn’t look like that big of a job, so I jumped in. Indeed, not that big of a job, and the mechanical part was completely finished within two hours.

However, as go most things with car repair, occasionally, Mr. Murphy and his laws show their ugly face. I guess that I shouldn’t blame ol’ Murph, because I don’t know who he is or was, so he can’t defend himself, and more importantly, I should have done my homework. But, I was a professional, or at least I used to be, anyway, back in the day, and who knew that there was such a vast difference in the way things are now versus the way things were back then. After all, I had been out of the professional repair business for over sixteen years. But, like sands through the hourglass…

Anyway, on to the grass roots of this post, I have a word to the wise. When working on a late-model General Motors product, such as mine, do some research first, even if you think that you know what you are doing. As it turns out, GM uses this expensive junk in the cooling system called Dex-Cool, their own secret recipe for coolant. It’s a nice red color, but opening the radiator showed me that the consistency is about the same as regular Prestone, Peak, or any other commercially-available aftermarket antifreeze. Now, I did not completely flush the cooling system, I only opened it and drained out what I needed to in order to get the pump out and not make too big of a mess. After putting it all back together, I just added the new coolant (Prestone) to whatever was left in the system. THIS IS A BAD IDEA. Read on…

I ran the car to operating temperature, waited for the electric radiator fans to kick in, and closed the radiator. As an additional note, I did not notice at this time that I just created a slopmonster in my radiator. I drove the car for a while, and although it did not overheat, I had virtually no heat in the cabin. Convinced I had a huge air bubble in the system, I got back home, and tried to burp it out, but as soon as I opened the cap, I saw this toxic hazardous waste resembling spent plutonium oozing out of the radiator fill neck. I have never seen spent plutonium in its natural state, but I would imagine it looked like this. Now I started to do my internet homework about purging the air, as these newfangled cars have some high spots that hold a pocket of air that just won’t come out no matter what you do, a couple of guys said to run the car with the cap off, and rev the engine up to about 2500 RPM, and hold it there for about 30 seconds. Keep in mind that these 3800 motors are fly by wire nowadays, so there is no linkage to hold the throttle open while under the hood, so you gotta sit in the care to do this, leaving the engine compartment unattended. This turns out to be another bad idea. As soon as you let off the gas, coolant pours out of the fill neck and all over the AC compressor and belt, causing it to jump right off the motor, wrapping itself around the crankshaft pulley.  Glad I bought another belt beforehand. Searching more blogs, I learned the true reason, which was not necessarily an air bubble. A few posters in the blogosphere indicated that the Dex-Cool and aftermarket coolants just don’t play nice in the sandbox together. Additionally, I felt the heater hoses, and sure enough, one was red hot, the other only lukewarm. Now I feared that I wrecked my otherwise beautifully working heater core.  As it turns out, even though the Prestone bottle says it’s compatible with other coolants, Dex-Cool is a beast all its own. Adding the Prestone to the Dex-Cool immediately created this red mud-sludge mixture in the system that clogged up EVERYTHING.

Thoroughly frustrated, I waited a day or two before doing anything else, I contemplated taking it to a shop to professionally flush the system, although the web forums say that might not work, also thought that I might buy some of that miracle flush stuff from the local Pep Boys, but I dismissed that thought, why would I want to put more junk in the system, I just opted to do it the old fashioned way. I took off both heater hoses and backflushed the heater core. Well, the slop that came out of there was interesting. More of that spent plutonium. I ran a steady stream of fresh water from the garden hose through it until it ran clear, and then the other way until clear again. Same thing through the water pump outlet and return. Opened the cap and let that run clear again. I might also mention that I did this without the motor running.

Once I was satisfied that I ran enough water to completely use up the entire deep Magothy aquifer running under this blasted island. I drained the system again. This time I filled it up with more good old Prestone, this time using the 50/50 premix. Offer up a sincere prayer to our Creator, and start the engine again. Repeat the process again, but just let the car idle until I could see normal circulation in the radiator, top it off. Fans kick in, and top off the overflow. Now for the moment of truth—turn on the heat, and lo and behold, God answers prayer. Immediately it gets to about a hundred degrees in the cabin, temperature gauge normal, and all is well in the universe. Road test the car one more time, and now I can put the tools away and wash my hands.

All that to say this—any of you guys out there that might be thinking of taking on this project, make sure, make real sure, that you either use more Dex-Cool to top off your system, if that’s what is in there. Or if not, completely flush out all the Dex-Cool and replace with the aftermarket product of your choice. Also, DO NOT rev the engine for any length of time with the cap off. All should be well if you just do it the normal way.

Thanks for listening…GWD