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Backroad,I found that with WTF there are so many fines in it that will coke up the injector very quickly even with filtering through first a 10 micron followed by an element rated at 2 microns, that it is clear much finer 'polishing' is necessary on this type of used oil. Diluting the 2 micron filtered WTF with diesel did not stop the coking and engine fouling, it only reduced it linearly in time with the ratio of added diesel. i.e. 50% diesel and the thing ran twice as long before geting really sick. I was using my 1.5 Litre, 4-cylinder VW diesel engine in a power plant for this testing.