I've noticed a few times I have started up the car after its been sitting for at least a few hours, and it will emit blue-ish exhaust. It only does this when I start the car, and its only been a few times (always when its hot outside and my cars been outside, dont know if that makes a difference). The first time it happened, I was actually getting ready to drive to get my oil changed, so I figured maybe it was the old oil - but even after my oil change it has still done it a few times. Any ideas?