I have a Toyota Camry XLE 2007 which has only about 15,000 miles on it. The person before me never really drove it, but now that I have been driving it I've checked under the hood. I found that the pink coolant in the overflow reservoir is very much below the "minimum" level mark. In what way should I refill it? Should I empty all of the current coolant and then put new stuff in (considering it's 5 years old, yet still has a nice pink color)? Or do I simply add coolant to the reservoir?