How many miles? does it have "DexCool" in it? Have you ever had the cooling system flushed?
If it has Dex in it for more than about 80,000, you may be screwed, because the stuff, if it gets oxyen in it(ie:exposed to air for long periods of time, alot like brake fluid and moisture) the stuff will oxidise aluminum. That will eat away at the radiator, intake manifold, heater core, thermostat, ect. and can jel and plug passages. The catch is if you flush it, it may disolve the buildup pluging the intake gasget from where it ate away aluminum and having a shitty gasget. This will cause a sudden and possibly severe coolant leak at the intake manifold.
If you flush it with that Prestone stuff that will work with anything, you will prevent further problems.
P.S. Any spelling errors, I didn't see, so go easy.