I have a 60 seiries detroit deisel in a 2000 volvo vnl The motor used to start right off even if it had been sitting for a few weeks. Sudddenly it began taking 10 second of cranking before it will start, even if it has been sitting for less than one hour. I replaced the check valve at the back of the cylinder head a few months ago ,because allthou it would start right away it would sometimes quit after it ran for 15seconds or so. Replacing that valve did't fix that problem but I found if I keep the fuel tanks full when I park it I don't have that quiting problem. The truck has 1.2 million km or 780 thousand miles.