Originally Posted by sdude2k2000
I hate to pile on... but Roadrunner1 has done extensive UOA analysis and should be considered someone to be listened to on this one. His long track record convinced me to switch to 10w30 in my own truck back in 2014/2015. My truck was bulletproofed and tuned... often with a hot tune specifically for trucks that had been head studded (hotter tune gets better mileage). I know you and I already chatted in your oil filter thread so I won't keep going, but the 10w30 advise really is the best advise.
If you want to run a 5w40 - that's completely your prerogative obviously. But much like my advise in the other thread was, I'd recommend heeding it here too. Worry about things like effective temp & voltage monitoring, replacing the weak alternator with a stronger one, ensure your FICM is over 48v at all times and replace if lower, flush any silicate coolant if you have it and get some silicate free ELC in there (add a coolant bypass filter while you're at it), upgrade or get rid of the stupid EGR cooler. Then pray your head bolts hold everything together and you don't need to do a head gasket... or if you do - that it doesn't nerf your heads in the process.
Those are the things to worry about - not which grade of oil you use or which oil filter to use. This one really is simple. If you want to use a 5w40 - no problem! It will run fine - please don't overthink it. Heeding the advise from those of us that have had these trucks and spent quite a bit of time (and money) wrenching on them isn't a bad idea either... we can't all be wrong - can we?
From some one that works on these every day, i will say he is right, regarding things to be concerned about. This engine has its weaknesses, but oil is not really one of the them. Head gaskets, EGR cooler, and oil cooler are the big three, followed by the FICM, fuel injectors and sticking union ring in the VGT turbo. Good batteries and a healthy are also a must. Being an 04 model, also possible it has the failure prone swash plate style High pressure oil pump.
Good luck with the truck. Tel your son to do some research on the problem areas and learn to fix the Truck himself. Paying someone to do it won't be cheap.
Also just a little education, these injectors suffer from "stiction", but not from "Pintle", as your original concern. The spool valve the solenoids control sticks mechanically. The spool valve directs oil flow to the intensifier piston to fire the injector. The spool valve can stick from debris in the oil, a weak solenoid (open or close solenoid), poor injector supply voltage or injector harness problems.