I know this isn't the Bronco Forum but this is the closest thread I could find to my problem(s). I just pulled my radiator, thermostat, & right side heater core hose. I took the thermostat out of the housing, placed the housing back and flushed it out the bottom radiator hose. Then back flushed through the heater core hose to remove coolant/sediment from the block as the drain bolts on the Bronco 5.0 are a nightmare. Anyway, flushed til it was clear water coming out bottom radiator hose. I then installed a brand new Vista Pro (Ready Rad) OEM aftermarket radiator and a Victor Reinz Thermostat gasket (w/victa foam, so don't have to use sealant). Connected everything back-up, filled rad. w/coolant, turned heat on high & cranked Bronco. After about 3-4 minutes, my coolant overflow bottle began overflowing with pinkish milkshake consistency fluid. I immediately turned it off and let it cool. Then, opened the new rad. lid and there is also tranny fluid in the rad opening (pour hole). What in the H**L HAPPENED? Yes, it is tranny fluid and yes, it is the rad. w/the tranny coller built-in w/the two tranny metal pipes going vertically into the rad. just below the opening (pour hole)! How is this suppose to work anyway? I mean if I look into the neck of the opening (pour hole) of rad. about 2" down is the top tranny hose connector which is obviously going straight into the neck of the rad. where you pour the coolant, so how are they suppose to keep from mixing? And, I know they're not suppose to. Luckily, it's not my only transportation so, I will keep it parked until I figure out why it happened and how to fix it. I initially thought that I'd undo all the hoses and pipes, drain all the BRAND NEW coolant, flush & reverse flush again, & refill w/new coolant but now I'm thinking that if there's an issue with why the tranny fluid is going into the rad, then it'll simply do it again! Any advise will be welcomed!