Hey guys looking for some opinions. I have an 02 WJ 4.0

New to me only have had for about a 2000 miles the jeep has 80k on it . A couple of weeks ago I had some smoke come out of the grill area upon starting the vehicle. I was a little surprised but it didnt happen again until 2 weeks later my wife took it to work and upon starting it in the morning and staring in the evening it seemed to happen to her as well. Well I hooked up a pressure test for the coolant system and it seeemed to hold pretty well. I pressured it up to about 18psi and over the course of 5 minutes it slowly and i mean slowly fell 2 psi. I could see no leaks anywhere. Any suggestions as to what might be going on here? btw no idiots lights have gone on and the temp gauge indicates all is well.