5W40 or 15W40 in 6.7 CTD?

rhagfo wrote:

otrfun wrote:
If Ram didn't require a 6-mo. OCI (truck's still under warranty), we'd probably use 5w-40 (3 gal. ~$60). However, we can't justify the extra expense for synthetic every 6-mo. Only put about 5k - 6k mi. on the truck between each 6 mo. oil change. We typically use whatever brand of API CK-4, 15w-40 that's on sale at Sam's Club or Costco (3 gal. ~$30).

Well even if it is a bit more I like to be constant with the oil I put in my engines, and like it to be good quality.

This is part of the reason why, this is the tappet gallery on our 2001 Ram CTD at 300,000 miles.

Granted, 5w-40, being synthetic, probably provides better protection under extreme conditions (i.e. operation at or below 0 deg). However, we've come to the conclusion it's not enough added protection under normal conditions (our M.O) to justify spending almost twice as much money for it every 6 mo.

Bottom line, we follow Ram's recommendation to use API CJ-4/CK-4, 15w-40 when temps are above 0 degrees (or 5w-40 synthetic when temps are 0 and below).