I noticed an oily grayish pink clumpy stuff in the radiator.
The truck runs fine and the temperature is not hot.
I flushed the old coolant out and refilled but the stuff came back.
I think it might be a leak between the radiator and the automatic transmission oil. Is there a way to check or repair this problem?
2001 3.0L ranger.

 

One of the things you can do is check the auto trans fluid level. If it has gone down there is a good possibility the trans cooler is leaking into the cooling system. As you can see trans fluid and anti-freeze don't mix too well and worse is the damage the coolant can do to the internal parts of the trans when you shut it down and there is still pressure in the cooling system pushing coolant into the trans. If you see any coolant in the trans , it would be wise to stop running the vehicle and drain the trans ASAP.