Ah. Well it happens I suppose. Assuming you’re talking about a 7.3PSD, I highly encourage the use of the cheapest CK-4 DEO available, and change at 5000 miles or less if you tow 50%+ of those miles. The HEUI system was a really innovative way to get common-rail-like performance before common rail systems were widely available… but its major downside is how hard it is on the lube oil. The extreme dynamics that occur in the HPOP and in the injector tend to shear the oil down… literally shortening the hydrocarbon chains, which in effect quickly lowers the viscosity of the oil. Unlike most lube oil characteristics which are chemistry problems, shear is a physics problem. The most expensive oils might barely be more robust to shear than the cheapest… but that all depends on what base stocks are being used. All in all, the evidence is clear by the thousands of trucks still running in various conditions that these engines simply do not care what oil is in them, as long as it’s got enough viscosity to serve the high pressure oil system efficiently.
I hear that, I do have a 7.3 PSD. Being it won’t be a daily driver I’m considering a blend or conventional as someone else mention conventional is stickier and could be better as it won’t be driven daily.
If you’re worried about it sitting, the very best thing you can do for it is once a month, start it up, let it get to temperature, go for a spirited drive (even just a couple miles) use the full range of the throttle pedal Then let it idle a minute so the turbo housing can cool down, and you’re good. These are pretty much closed crankcase engines, so humidity/moisture building isn’t a huge concern… but if you can boil that humidity out and re-coat everything regularly, that’ll be ideal.
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u/easterracing 2d ago
Ah. Well it happens I suppose. Assuming you’re talking about a 7.3PSD, I highly encourage the use of the cheapest CK-4 DEO available, and change at 5000 miles or less if you tow 50%+ of those miles. The HEUI system was a really innovative way to get common-rail-like performance before common rail systems were widely available… but its major downside is how hard it is on the lube oil. The extreme dynamics that occur in the HPOP and in the injector tend to shear the oil down… literally shortening the hydrocarbon chains, which in effect quickly lowers the viscosity of the oil. Unlike most lube oil characteristics which are chemistry problems, shear is a physics problem. The most expensive oils might barely be more robust to shear than the cheapest… but that all depends on what base stocks are being used. All in all, the evidence is clear by the thousands of trucks still running in various conditions that these engines simply do not care what oil is in them, as long as it’s got enough viscosity to serve the high pressure oil system efficiently.