Just noticed there is some transmission fluid in the radiator. We had transmission worked on a couple of years ago. What could be causing it. Transmission is working fine. Could this be the trans cooler?

 

Yes thats the only place the two fluids can come together

 

Welcome to the forum.

Disconnect the two transmission lines from the radiator. Block one, apply a vacuum to the other to verify if solid or leaking.

 

disconnect both lines. Block one, shoot some air in the other and see if you have bubbles in the radiator.

Or, jump to the obvious conclusion and replace the $40 radiator before you wreck a $1500 tranny.

There is no physical way for transmission fluid to be in the coolant other that a failed radiator. None.

 

X2, It has to be the radiator. Cheap fix and hey, it'll cool better with a new radiator and the new fluid you'll put in. Win, win!

 

Likewise, I'd check the tranny to make sure there isn't coolant in it. When the trans is in park, coolant under pressure can flow into the pan.