I need to flush the coolant in my 69 z/28. The question I have is what should I put in the car coolant wise? The stuff that is in there now is orange and that is what was in the car when I bought it. I have no idea what kind/color came in the car originally. I have no idea what is best to put in the car now. Should I change the thermostat just for good measure. What temp thermostat should I have in this car? The car is stock so it's still the good old 302.

changing the thermotat is good cheap insurance. the orange coolant you describe is probably dex-cool. i have a 180degree thermo in my 302. i also added a bottle of redline water wetter. i'm sure others will chime in. hope this helps.

I would flush the system and put a good anti-freeze back in along with the same size t-stat thats in it now. I would recommend just buying the pre-mixed stuff unless you have access to deionized water.

Water wetter is designed to work with straight water better than with antifreeze.

Be sure to check the hoses, all of them, for their condition also. Fan Belt?

As said, Premixed 50/50 is good to use.

dont mix the dex-cool with the generic green coolant, as they become caustic when mixed and usually eat intake gaskets...if you flush the block and lines, you can use either coolant, though...i usually run a 180 also because my car usually only see`s summer use, and invariably, when you`re in a cruise, you hit a traffic jam...lol...

I use regular glycol coolant at 50/50 mix. With the JohnZ vacuum advance mod, 18 deg initial and the HB City repro radiator I run in 105 deg weather and no over-heating at all. I have not heard the fan clutch come on yet. More info than you asked for.:D

Here is a disscussion on anti freeze
http://www.jowett.org/forum/viewtopic.php?t=266&highlight=anti+freeze