Just get it changed. Its not expensive.
antifreeze
Melting Slicks
Joined: Apr 2010
Posts: 3,191
Likes: 53
From: Tucson Arizona
Your manuals that came with the car will have your answers and will base it on mileage or time whichever comes first for all required services. If you run it for over 5 years it loosed its capability to prevent damage to the cooling system, especially the radiator and water pump.
My 2007 had the flush and refill done at the dealer at 5 years and 6,500 miles and it is critical to be done correctly to insure that there are no air bubbles that can cause the car to overheat. The dealer spent an extra half hour making sure that the car cooling system was air free. They also add an anti corrosion additive with the new coolant.
That is what I use to determine when I need to do any single service item.
From my 2007 manual:
Engine Coolant
The cooling system in your vehicle is filled with
DEX-COOL® engine coolant. This coolant is
designed to remain in your vehicle for five years or
150,000 miles (240 000 km), whichever occurs
first, if you add only DEX-COOL® extended
life coolant.
Team Owner
Joined: Aug 2006
Posts: 25,105
Likes: 3,156
C6 of Year Finalist (appearance mods) 2019
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Race Director
Joined: Mar 2010
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From: T-Town WA
2016 C6 of Year Finalist
Pro
Joined: Jan 2014
Posts: 577
Likes: 22
From: Longview Texas
Had mine done earlier this year. I have an 06 with at the time had 10k miles on it. Had a dealer flush the system when it was in for some other work. Coolant looks alot better than it did before the flush
Le Mans Master
Joined: Jan 2006
Posts: 6,800
Likes: 2,653
From: Down south in Dixie
Drifting
Joined: Jun 2008
Posts: 1,746
Likes: 35
From: Jupiter Fl
I will change anyones coolant (Corvettes for a $100 bucks) It will include new Dex Cool anti freeze, draining and flushing the old coolant, Disposal of the old coolant and your choice of a cup of Coffee or a Beer while you wait !! 
Le Mans Master
Joined: Oct 2005
Posts: 6,652
Likes: 2,106
From: Left Coast, San Diego
I just did my 2010 this morning. Drain and refill. Very easy. Took about an hour. Bought a gallon of straight Dextol and 1 gallon of distilled water. Cost under $30.
Last edited by Vet Interested; Oct 11, 2015 at 04:43 PM.
Race Director
Joined: Sep 2007
Posts: 16,557
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
The GM 5 year/150,000 mile recommendation is based on the national average of 12,500 mile/yr usage. It accounts for expected heating and cooling cycles and loss of additives during the running time required to acquire that mileage.
Since there is no expiration date on the containers, it's logical that age alone will not create a loss of the additives.
Nearly all maintenance recommendations are based on the expected half-life of the products, since the average car owner tends to go beyond the recommendation anyway and it gives the mfg an out for any warranty issues.
So, just change it when you feel that it gives you the warm fuzzies.
Since there is no expiration date on the containers, it's logical that age alone will not create a loss of the additives.
Nearly all maintenance recommendations are based on the expected half-life of the products, since the average car owner tends to go beyond the recommendation anyway and it gives the mfg an out for any warranty issues.
So, just change it when you feel that it gives you the warm fuzzies.