You can get one of those little devices that measures the antifreeze concentration from an auto parts store for a few dollars. You don't want the mixture to be a lot more than 50% antifreeze because then its ability to aborb and transfer heat will be reduced. i.e. if the mixture was 100% antifreeze it would abosrb less heat from the head and not cool as much during its run in the radiator.

If you want to take a little time, your best bet would be to drain and refill the system or just test the mixture.

Cheers. -Ali

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record