This engine blows white smoke when first started. As the truck warms up, the smoke turns to the color blue, maybe even black. I drove this truck for a half hour and proceeded to lay a nice smoke screen the whole drive home, lol. I also heard a slight knock, upon acceleration, but the noise stopped as the vehicle speed increases. Oil pressure is fine, coolant temperature was normal, when I got home, there was a hint of oil in the overflow tank. I am going a compression test tomorrow morning, that should provide some answers. Any other ideas? 
David
David