Zillions of cars use Dex-Cool and many more run Dex-Cool clones.
As mentioned above, the stuff doesn't like to be mixed. There's no telling what has been thrown into your cooling system.

I'd just buy some Volvo coolant on Amazon. With or without "Prime" it'll be cheaper than driving that distance.
Flush the mystery mix with hose water. Get excess distilled water (5-6 gallons) at the grocery store.
Mix one quart of distilled with the concentrated coolant and keep it aside.

Finish your flush with distilled. Drain the radiator and add the 3 quarts of concentrate. Top off with the 2 quarts of coolant you premixed.

You'll be a tad over 50% mix and be in coolant heaven.