Engine Coolant

I have a Ford Taurus and I was wondering if you are suppose to change the anti-freeze or just keep adding to it? Will it harm the vehicle if you don't change it?

It depends on the type of coolant you have in there now and the amount of use the car gets.

Over time, the corrosion inhibitors in most anti freeze will simply become less effective, allowing corrosion damage to internal engine components, especially aluminum parts. At worst, after years of neglect, aluminum components, like cylinder heads, intake manifolds etc (depending on engine design) may start to leak and need replacement.

Generally, anti-freeze does not lose its freeze or boil-over protection as it gets older, unless its been topped up with plain water.

The coolant should be periodically replaced.
At this time, the cooling system should be flushed properly to remove any accumulated debris.

For best results, the green anti freeze should be flushed and changed about every two years, for normal use, although lots of cars go longer than that with little harm, especially if you rack up lower than average miles.

I recall the orange/red coolant is a different formula than the green and lasts longer, 5 years or more between changes.

Have a look at your owners manual and see whats recommended for your particular car.

I also recall some companies sell little bottles of corrosion additives designed to be added to existing, older coolant to extend its life between changes, although I have no experience with such products.

The red/orange coolant has different protection packages than the green coolant. It is silicate free. For best results when dealing with coolants such as Dex Cool it should be changed more frequently than the once advertised 5 years 150,000 miles. There have been many problems associated with the use of Dex Cool and some of it has been attributed to "owner neglect" since the longer duration that it is supposed to last, most car owners don't think they need to service it as often. GM is now recommending that Dex Cool be changed more frequently than the previous 5/150. They even have gone as far as not placing stickers in the engine compartment with the 5/150 recommendation any more. If your vehicle does contain Dex Cool, keep an eye on the level in the overflow tank, and keep the level where it should be, because when the level drops, air can be introduced into the system and cause sludging . Watch for a sudden drop in the level, as that could indicate a leak in the system. It is also a good idea to thoroughly flush the cooling system when you replace the coolant with a fresh mixture, and replace the radiator cap as it has been found that some caps can fail and introduce air into the cooling system.