Our cars use long life antifreeze that should not need maintenance for 50,000 miles (iirc). I wouldn't recommended mixing antifreeze with what's in the car. I don't know how much you know about cars, but make sure you are checking the level in the overflow tank (see owner's manual for instructions). You shouldn't be low on coolant unless you have a leak. I would check for puddles under your car before you get in it. If you are using A/C, you will probably see water under your car, this is normal. If you have questions, just ask. I'll be happy to help.