Q. I have a 2003 6.0 starts fine first time during the day after it gets up to midway of the engine temp gauge, which from new has been the norm, if I turn the engine off it will turn over but not start until engine cools down. Idle RPM is about 600 if im driving down the road and have to stop or slow down to 600 rpm engine dies and wont start until it cools. Do you have any suggestions. Thank you !!!!! - Matt

A. Hi Matt,

I would guess you have a high pressure oil leak. It won’t start when warm because the oil thins out. Once it gets a little cooler it can overcome the initial 500 psi the computer needs to see before it will fire the injectors. If the leak is bad enough the pump will not be able to overcome the loss in pressure at lower engine rpms and the engine will die.  I would start by doing a pressure test of the high pressure oil system once you confirm that it is not building pressure when trying to start when warm.