Problem with B20 and anything above B5 is OIL POLYMERIZATION that can occur in any modern diesel that has a diesel particulate filter that undergoes regeneration.
Durting DPF regeneration, fuel is injected into the exhaust during the exhaust stroke. Some of the fuel always leaks past the rings. Fuel that is high in biodiesel can mix and dilute your engine oil causing it to be less effective and requiring more frequent oil changes. In some cases the biodiesel component can interact and cause the additives in the oil to do some nasty things, i.e. polyermize.
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A tank or two when you on a long trip won't hurt much but regular use should be avoided at that high level. I personally like to mix to B5 level which lubricates the fuel, keeps everything clean in the fuel system, increases cetaine, and cleans a little burner but not noticeable with a DPF installed.