Flushing my radiator. Just got the car and it's full of Sludge.

Should I add dexcool again or switch to the green stuff?

 

Despite it's reputation, Dexcool is fine. GM recommends it , but you can use either. The problem is the plastic lower intake manifold gaskets used in production that are softened by the coolant. They should be replaced with Felpro metal ones. Do you know where the sludge came from? Did you have a LIM leak? I've had a nuisance problem with sludge in the coolant of my '00 SS that got in before I replaced the gasket. Sludge keeps coating the probe of the coolant level sensor causing a false reading. Had it professionally flushed at Jiffy Lube, but still have the problem, even after replacing the sensor. What flush method will you be using? Let us know your results.

 

I agree with Plumbob, but let me add, the plastic/nylon LIM gaskets he mentions, I have seen them fail equally with traditional green coolant. The material was crap no matter what you use. He gave you the best advice, if you ever have to change them, switch to the FelPro metal core gaskets.

As for the sludge, any coolant when neglected from regular flushing can do nasty things. You may want to consider a "flush kit" (and a flush additive while flushing the system to break up the gunk and force it out).

Keep up on regular maintenance and it should not be an issue.