My '91 Camaro sat for 9 years,give or take a year. It was my dad's,but I worked my *** off for it. I've changed all fluids except rear differential and coolant. I've cycled the thermostat and fan to make sure the coolant flowed. I let it cool off;then I took the cap off,and saw the coolant is still a bright green. Would you say it's fine the way it is,or just change it anyway? As far as I know it does the job as it's supposed to.

 

Change the coolant.

Assuming that the coolant that's in there is common green Prestone-like stuff, the silicates in it will start to precipitate out of suspension after a coupe of years. This will deposit within the cooling system and will plug the radiator and heater core if left in long enough.

 

That's a good question. I often wondered about this myself. Rock Auto had an informative story on how to check your coolant. The meat and potatoes of it was: using a multimeter (analog or digital) set to lowest volt setting, place the black lead on a good ground and place the red lead in the coolant. A reading of less than 1 volt indicates that the coolant is still good. Mine measured 0.12 volt which was good and I didn't change the coolant. Here is the article.

http://www.rockauto.com/Newsletter/archives/6-4-15.html

 

Pull the plugs out of the bottom of the block and flush it real good.

And while you are at it, flush the gas tank. There is all sorts of crap in there after 9 years too.