Some no start help would be great

[NYMustang50]

I drive a 99 f550 flat bed tow truck trucks got about 260k on her now and it wont start when the temps are below 40 anything at 40 and above shes fine but once it hits 39 or lower she just doesn't seem to want to start. I had a local diesel shop put in a new hpop and ipr valve or icp sensor a few months ago but that was also maybe 15k miles ago too. Brought it back to them they diagnosed it as bad hpop again and all 8 injectors are bad. now the truck runs fine and great at and above 40 degrees outside like she has ever since its been in the company but she just doesnt want to start in the cold. Is there anything I can look into maybe do some test to diagnose my self and figure this out? Oh another thing since about after two weeks of the new hpop the thing weeps oil out the weep hole till the truck gets to normal operating temp is this normal?

[jesilvas]

Oil leaking normal?
NO. No vehicle should ever leak anything. Sounds like your "diesel" shop needs to change professions.
Did they even think about the glow plugs or glow plug relay?
There are a few stickies on here in the 7.3 sections on how to test the GPR and GPs.
Batteries good? Test the individually, both voltage and load testing. 850CCA minimum. Good battery connections, cables, starter connections, ground connections.