'93 with 140k miles and the original radiator, pinhole leak on top. Got around to replacing it today. Poking around in there I was surprised to see a tranny cooler mounted in front of the ac condensor, was this ever a factory option?

Anyway... I have the fan shroud mounted on the replacement and ready to drop in, old hoses are still good but the radiator was toast. The old coolant didn't look bad though. I have two gallons of zerex 50/50 for asian vehicles, can I just top off with that and "burp" the system and be set, or do I need to flush? If I need to flush, what would be the easiest way to do that? If I just flushed with DI and drained via the radiator drain plug, I'd be worried about the ratio being messed up since I'd be adding premixed coolant when there would presumably still be DI water left in the system. Thanks