On the subject of oil changes, Anyone know the difference in oil change intervals for I6's with oil filters, and without oil filters?

My 51 does not have a filter, but my 59 has one from the factory. I really dont drive them much to change it regularly, and probably end up pouring in fresh rotella about once a year on average. It would probable be a good idea to ad a filter on my '51.


1951 1/2 Ton 216ci 4spd
1955 3/4 Ton NAPCO 235ci 4spd
1959 1/2 Ton stepside 235ci 4spd