OP: You're fine. If you mix orange & green coolant together, that's when the problems begin.
Dexcool uses Organic Acid Technology (OAT). The green is generally ethylene glycol-based.
When the two are mixed, a gel forms, and that clogs up the coolant system.
Your engine can run one or the other, but not both.
I use Dexcool in my GM vehicles. When I travel far from home (towing, camping), I always make sure I have extra coolant.
If you ever get into an emergency situation, and need to add... use water if no Dexcool is available. Preferably distilled, but if it's a choice between sewer water and a different coolant... I'd use the sewer water. No joke!
Can you switch? Yes, but you have to remove *all* the old, and flush thoroughly with water, before introducing the new. Reason to switch? For me, it would be potential scarcity of Dexcool. But outside of that, I'm fine with the Dex -- it costs no more, and lasts as long.
As far as change interval... the factory fill is good for 150,000 miles, per GM. However, once it's removed, the interval becomes more time-based, and you generally see 3 years specified (for most vehicles, not just the ones using Dex). If you do a straight drain / refill at that interval, you'll likely never have a problem with your cooling system, and you'll never need to worry about disturbing the 50/50 balance.
Might it last longer than 3 years? Probably, to tell the truth. But two bottles of coolant, and 2 gallons of distilled water is pretty cheap, at 3 year intervals. That also gives you a good opportunity to change out wear components like hoses, etc., as needed / warranted.
Signs to look for to know when it's time to R&R...
- Good coolant will leave a very slightly oily or greasy or 'slick' residue on your fingers. That indicates lubricity in the system and keeps things like the water pump in good shape.
- As coolant loses it's protective capabilities as an anti-corrosive, you may see coolant get a brownish tinge as it gets older. The brown is corrosion. If there's one thing I don't like about Dex... it's that it can be hard to tell if it's starting to get brown, as it ages. A yellowed coolant reserve / recovery bottle doesn't help, here, either.
If you have either of the two conditions above, don't just drain / refill. A flush is needed, at that point.
And then there's the universal coolants, the clears, the yellows, etc.
I would not mix these, even though that's their selling point (like someone with type 'O' blood). I suppose they 'work'... but will they work as well as the coolant you generally run? No, because anything that's 'universal' is going to have tradeoffs.
The only 'universal' coolant, in my book... is water.
Probably should've clarified a bit.
