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In regard to the wear on internal metal parts in injection pumps - especially rotary pumps - it's been known for many years - what they can tolerate, and what they cannot. CAV, Stanadyne, the US Military, et. al. have done a lot or research and published it. Also, wear is not the only issue. When viscosity gets low, pumps can leak internally even when wear has not occured. When we buy fuel - I assume we'll never know, for sure, what the actual specs are - on the fuel going in the tank. That being said, - a viscosity of 1.3 (1.3 square millimeters per second) and above seems to be the "breaking point." Anything thinner than that, leakage, lower lubricosity and early wear occurs. United States #2 diesel fuel is supposed to have a viscosity of 1.9 or above at 40 degrees C.
United States #1 diesel - a min. of 1.3.
These specs apply equally to low-sulfur fuel and are based on the ASTM specs cited by dej. In Europe, the minimum viscosity and cetane is higher. In regard to "historical" wear in Farmall injection pumps - my ownly experience is with repairing Roosamaster pumps on Farmall/IHs, along with Roosamaster/Stanadyne and CAV rotaries on Deere, AC, and Ford equipment - since the early 1960s. Personally, I've seen very little metal parts wear in those pumps. The many early failures due to shattered plastic parts, shaft umbrella seals, fiber pump vanes, especially governor retainer dampeners has nothing to do with lubrication. I also have seen a lot of corrosion damage - inside head& rotor assemblies and on cam-rings which I assume is from water-in-fuel creating acids. I HAVE seen metal parts wear in newer pumps - especially in Stanadyne rotaries. And, the US military has had extremely high-failure rates with new pumps not lasting 1000 miles - but they are related to thinner fuels than we get at the pump (hopefully). For myself - I just assume I cannot trust, for sure - diesel fuel at the pump - and I use an additive that has been tested and proven to be effective.
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