water in oil

It means you have water in the oil silly! Coolers can leak both ways. How long has it been since that repair? It may be just contamination from that or the work performed. Change your oil and keep a very close eye on it. You may have something else leaking like an injector cup. From now on when you have a question like this it is really important to mention what year/model truck you have and the type/model of engine too!

 

It's possible that coolant was in your crankcase at the time you replaced the oil cooler and is just now showing up. It's also possible that coolant went in to the crankcase when you changed the cooler. I would change the oil and continue to monitor it for coolant. That may be all that's needed.

 

when you say sign of water is the oil milky or just a few bubbles more info please

 

then an oil change and watching it is good enough for now
if it gets milky you have bigger problems
with bubbles you are probably checking hot oil
you might not even see that on a cold engine

 

It could also be a broke air compressor. Water coolant mixing in the head of compressor and being pushed back to engine.

Worse case scenario, cracked engine block or head.

 

Anymore coolant sence oil change