I just changed oil in both my vehicles yesterday (4k OCI for the Cad 3.6 and 5k OCI for the Honda Odyssey). The Cad had Penn Plat HM 5W30 and the Honda had Penn Plat 0W20. Both vehicles had Fram Ultra filters that were changed at the last OC. The oil was very dark and thick in both vehicles; if I understand correctly, dark thickened oil indicates it is contaminated and time for a change. This was quite surprising, given that Penn Plat has always looked pretty good after 5k. The only new item last OC was the Fram Ultra. Does anyone have any ideas as to why the oil deteriorated so rapidly, and if there is anything I can do to prolong the life of the oil? I am fine with 5k OCI, but want to make sure I shouldn't be going with shorter OCI.