I hope your putting 1-1/2 quarts of oil in your 10,12,14,& 16 hp Kohler's. See my third sentence in my above post. Shell Rotella has plenty of ZDDP. That's what I use. The valve springs in Kohler engines have very low spring pressure, not at all like a high reving V-8 with high lift long duration racing cam shafts. The need for ZDDP is directly proportional to the amount of valve spring pressure. ZDDP doesn't make me loose ANY sleep.Thank goodness its only approx. one quart! What do you think about the lack of zinc in modern engine oil?