My son is still in college and bought a used truck: 2004 Ford Super Duty F350 with the Navistar "PowerStroke" 6.0 liter V8 engine. Modern diesel oils were developed for the latest diesel engines, of course, so I'm having trouble finding which would be best for this older engine. Would appreciate BITOGer wisdom on this one. Detail below for reference. I was with Cummins for 22 years, retiring in 2016. I researched the old Navistar 6.0l PowerStroke engine and found it uses Gen II HEUI Fuel Injectors. The HEUI of course is "Hydraulically-Actuated, Electronically-Controlled, Unit Injector", developed with Caterpillar. It was an interim EPA emissions reduction strategy prior to HPCR (High Pressure Common Rail Electronically Control AND Actuation). The problem with the HEUI was using dirty engine oil as a hydraulic fluid often caused sticky injector pintles, requiring injector replacement. Cummins used "HPI" that used fuel as a hydraulic fluid, varying the length of the injection plunger. It still used a mechanical cam to inject. CAT also had this on their bigger engines and called it "MEUI". Anyway, the boy's truck was a farm truck that was dealer-maintained, so a pretty good deal despite the other problems with the Navistar 6.0l engine. Being a 2004, Navistar had already addressed some of the problems from the 2003 launch. It "only" has 113,00 miles on it and is in good shape. Still, he had it diagnosed and it already had 2 sticky HEUI injectors, so he's having all 8 injectors replaced with rebuilt. He wants the correct engine oil for the new injectors to keep them as clean as possible for maximum service life. He should be able to get another 100,000 miles from this engine. The other problem with these injectors is oil flow. We live in the far north US, so cold start is problematic with a mineral oil. For this reason, I recommend using only synthetic year around. Synthetic also retards base stock oxidation breakdown - critical for HEUI injectors Finally, the higher pressure required to use engine oil as the hydraulic actuation for the injectors required a higher pressure oil pump, which made antiwear far more important than would otherwise be with standard engine lubricating oil pressure (40-60 psi @ rating). I don't know what the injector oil pressure is, just that Ford made a big stink about to the point when the oils went to API CK-4, they tested a bunch and found them "insufficient" antiwear because the newer engines took the ZDDP out and lowered the phos so as to not poison the new SCR EPA TIer IV exhaust catalysts. So Ford created an engine oil spec to demand the antiwear back, via new formulations. The spec is wss-m2c171-f1. I visited their approved oil list. The only 3 available in my region are: - Motorcraft Full Synthetic Diesel (of course), only available at the dealer (unknown price), Amazon $53 / gallon, and O'Reilly's $40 / gallon. A pretty ridiculous price for an API Group III engine oil, that Ford insists must be changed every 5,000 miles to prevent injector problems. - Valvoline Premium Blue Extreme, available from Amazon, Walmart, O'Reilly's for ~ $29 / gallon. That's within the range of acceptable pricing. - Shell Rotella T6, available all over the place around $22 / gallon. None of the Mobil Oils are approved except Delvac 1 ESP 0W-40. Mostly only available in Canada - I can't find it anywhere online. Which of those 3 above have the better recipe for the older HEUI engine? And please, no Amsoil diatribes about Signature Series API Group IV PAO being the best. Need to change every 5,000 miles to dump the soot from sticking the injectors. Ready, set, GO!!!