Thanks for the replies. I've got a new radiator and trans filter kit on order. I don't think this was going on very long, because once the ATF hit the cooling system, the resulting foam caused the car to overheat. I was only about 2 blocks from home. Wouldn't the ATF pressure be greater than the coolant pressure? I'm hoping the ATF was present in the cooling system longer that vice versa. We'll see. It was a stupid rookie mistake from someone who's been around a long time and knows much better. Just got sloppy and lazy.