when starting my 760 turbo diesel for the first time of a day, it fires then quits. it takes a number of attempts for the vehicle to start and stay running. once running it drives great and starts without trouble for the rest of the day, but the next morning it's the same tough startng situation.

all glow plugs are new and functioning well, my mechaninc checked the timing and says it's spot on and he checked the cold start device and said it seems to be set properly. the starter and battery are new. every tank has powerservice DFS and marvel mystery oil in it, and since it runs well once started it doesn't seem to be an fuel injector problem. it has Mobil 1 European Formula 0w-40 oil in it to ease winter starting.

it used to cold start (and continue running) with ease even down to 5 degrees. i don't know what happened, and my mechanic seems stumped too. any ideas?