I just purchased an 07 titan with 117k miles on it. The truck runs, drives, and idles perfect, but almost everytime I start it, LOTS of white smoke comes out the back then it goes away after about 10 seconds. I did find an empty bottle of GUNK in the back of the truck but Ive put almost 300 miles on it already so Im not sure if this is normal. I dont believe its a blown headgasket because the smoke goes away completely after 10 seconds.