I replaced the radiator in my '99 Accord EX 4cyl. (2.3L F23A1) today with a Murray radiator from O'Reilly's (don't buy, it's not a great fit). Everything went well enough, but the clamp on one of the ATF cooler lines is not holding, and as I was idling the engine and adding coolant, it started to steadily leak from the brass fitting at the bottom of the radiator.

Is the fluid coming out transmission fluid, or is it ATF cooler oil? It looks pretty dark, like oil, but the car has 156k miles on it, so it's hard to say what it is.

If it is ATF cooler oil, how do I refill it? (I bought a new hose and clamps to replace the leaking ones.)

 

It is ATF. Refill your transmission fluid to the correct level after you fixed the leak.

 

Make sure the hose you bought is rated for trans cooler use.....regular fuel line will not work, or a least for very long.