Thanks for the reply OM ! I guess you have had these discussion before and are tired of it ! My Friend (retired)had a 3406B with a breaksaver in his logging truck and with the steep mountain roads he found that the one time that he ran 15w40 it did not hold back like when he ran 30w ! In the Cat thread you posted 30weight is good to -15 which is about as cold as it gets here ! Thanks Glen