My family is a GM family. There have been a few exceptions to this. My
Grandma's parents owned a Ford Model T, found out it was a piece of junk,
and traded it for a Chevrolet. I owned a 1995 Ford Mustang GT for a few
months back in 1997 (great car). And my brother currently owns a Mitsubishi
I am the one that usually changes the coolant in my family's vehicles. I
remember back around 1996 or so, I was driving a 1985 Chevrolet Monte Carlo
and decided to convert it to the new red DEX-COOL coolant that had just came
out. When I say "convert" I mean doing my 22 steps below as to obtain a 60%
antifreeze to 40% water mixture. I later bought a 1991 Chevrolet Lumina and
then a 1992 Chevrolet S-10 after owning several other cars between those and
the 1985 Chevrolet Monte Carlo. I converted the Lumina to DEX-COOL. It
ruined a gasket that had to be replaced. The S-10 was even worse. After
converting it, it would blow smoke out of the tailpipe every time it was
started due to coolant leaking into one of the cylinders.
I decided to get rid of the S-10 earlier this month and bought a 1995
Pontiac Grand Prix GTP with every option imaginable. After a few days of
owning it, I checked the coolant to find that it was BROWN! That means it
hadn't been serviced for quite some time. I figured it was DEX-COOL so I
flushed the cooling system and poured in some fresh DEX-COOL. After doing
that, I found out it had conventional green instead so, after about 3 days
of DEX-COOL, I converted my car back over to green using Zerex 5/100
Coolant. I think I got the DEX-COOL out in time before it could start
eating away at gaskets and seals and start spawning that reddish brown mud
in my cooling system.
Now around 2000, I converted my Mom's 1995 Chevrolet Monte Carlo from green
to DEX-COOL. After finding out about my Pontiac originally having green, I
decided to convert her car back to green. I was SHOCKED to find that the
DEX-COOL had turned into that damned reddish brown mud. The throat of her
radiator and the radiator cap were almost ruined. It took me an good hour
of scrubbing the radiator cap with a tooth brush to get it clean.
I did the exact same thing to her car that I had done to mine. I used the
back flush tee I had installed in 2000, back flushed her car with the engine
running with the heater on high for 30 minutes, poured in a bottle of Zerex
Super Cleaner, had her drive the car on and off for about 6 hours, drained
the radiator, back flushed again with the engine on and the heater on high
for 15 minutes (I was happy to see the mud coming out knowing the Zerex
Super Cleaner had done its job), poured in a bottle of Zerex Super Flush and
ran the engine for 15 minutes with the heater on high to be sure all the mud
was gone, drained the radiator, hooked the hose back up to the back flushing
tee, and back flushed again for 30 minutes. I drained the radiator, took
out the overflow tank and cleaned it out with hot water, Dawn dish soap, and
a bottle brush. I hooked the overflow tank back up, closed the radiator
drain plug, put the cap back on the back flushing tee, and poured in Zerex
That was about a 3 weeks ago. After checking the overflow tank, radiator,
and radiator cap, I am happy to report that there is no mud and the car runs
All the above is my story with my experiences with DEX-COOL and conventional
green coolant / antifreeze. I will now explain what I think of conventional
green, DEX-COOL, and G-05.
I think this was a bad idea from the start. You would have to be a complete
moron to run any coolant / antifreeze for 5 years. A lot of people also
have the misunderstanding that they are not to touch it for 5 years. This
is just stupidity created by GM.
I think the 2 biggest flaws to DEX-COOL are that if it gets into contact
with conventional green directly or through the deposits left by
conventional green, it will form that reddish brown mud. If DEX-COOL comes
into contact with air either inside the cooling system or outside, it will
form either the reddish brown mud or the red "cement". This has been proven
by both owners of some 1996 - Present S-10s and owners of other GM vehicles.
I would probably recommend most folks stick with DEX-COOL if that is what
their vehicle came with, but a lot of brave people have converted back to
conventional green without any problems.
I think it is the best especially for GM vehicles. If you do an extremely
thorough back flush (the 22 steps listed below) you will get all the
DEX-COOL out. I would HIGHLY recommend using Zerex 5/100 Coolant which most
AutoZone stores carry.
I have not used this coolant yet, but keep hearing good things about it. It
is designed to work in new Fords and Chryslers and has been used for many
years by Mercedes and John Deere. I think GM will eventually switch to it.
Now if you would like to back flush the DEX-COOL or any other coolant out of
your vehicle, do it this way (you are responsible for what you do to the
vehicle you are working on).
1) Buy a few jugs of Zerex 5/100, either a Prestone or Zerex back
flushing tee, a bottle of Zerex Super Cleaner, and a bottle of Zerex Super
Flush. You might optionally want to go ahead and replace your thermostat.
2) After driving the car for 30 minutes or longer, open the radiator
drain cock, and let the radiator completely drain out. While you are
waiting, find the heater core hose that runs into the engine (not the one
going to the water pump) and cut it. Install your back flushing tee. Also
disconnect your overflow tank hose.
3) After the radiator is drained, take off the radiator cap.
4) Get your garden hose and screw it onto your back flushing tee
connector then put the connector to the back flushing tee you installed..
5) Turn on the water and wait for water to start coming out of both the
radiator drain and top radiator opening.
6) Turn on your engine with your heater running on high and let the car
back flush for 30 minutes.
7) Turn off the engine and disconnect your garden hose.
8) Wait for the water to drain completely from the radiator.
9) Close the radiator drain cock.
10) Pour in your bottle of Zerex Super Cleaner into the radiator.
11) Connect the overflow tank hose and top off radiator with water.
12) If you have bleeder valves for air, turn the engine on with the valves
open and wait for water to come out of them in a constant stream then close
13) Drive your vehicle for 4 - 6 hours which can be on and off and over a
few days. Be careful the outside temperature is not 32° F or lower as water
expands when it freezes which will ruin your radiator and your engine and
14) Repeat steps 1 - 12 except for step 10 pour in your bottle of Zerex
15) Run engine for 15 minutes.
16) Repeat steps 1 - 9.
17) You may want to take out your overflow tank and scrub it inside and out
with dish soap and a bottle brush. Be sure to rinse all the soap out of it.
When you install it back into your vehicle, you may want to fill it up with
water from your garden hose a few times and let it drain out through the
disconnected overflow tank hose.
18) Connect the overflow tank hose after the overflow tank has been rinsed
and is completely empty.
19) Pour in your jugs of Zerex 5/100 Coolant slowly until the radiator is
full of coolant. If it takes 1 1/2 jugs, then that is 6 quarts. If your
system holds 12 quarts, then you have a 50/50 mixture.
20) Fill the overflow tank with Zerex 5/100 Coolant until either the
overflow tank is half full or you reach the HOT line.
21) Repeat step 12.
22) That is pretty much it, but be sure to check your overflow tank and
keep the coolant level at the COLD line after your vehicle has sat for 6 or
8 hours over the next few days and get into the habit of checking it at
least once a week.