I read in the manual about not letting the diesel idle for extended periods as it will cool down and not burn all if the fuel causing varnishing. When we travel we sometimes take or dogs and while they can stay warm in the winter in the truck the summer is my concern. I would like to leave the truck running with the A/C on but will it cool down enough in 85-90+ degrees to varnish the cylinders. There time without us with them would be extremely limited and hardly ever out of sight, usually while eating or in a store where we can see the truck at all times. I try to never be out of sight of my truck due to my carrying a gun with me and in the truck. Okay, retired cop, some habits I refuse to break