since ford only sells 15w-40w oil for its diesel. I was wondering if it is ok to use a 5w-40w or 10w-40w synthetic oil. thanks for your help

 

diesel oil is primarily 15-40 ... and it has to be rated for CI. not sure if this helps, but i would use what ford reccomends, which i am pretty sure is only 15-40.

 

When the temperature gets to 30 F and below they recommended 10w-30, unless you are doing heavy towing. I use 5w-40 synthetic year round. The 7.3 can use either CH-4 or CI-4 rated oil. The 6.0 should only see CI-4.

 

My owners manual says use only 15w-40w API CH-4?SH. What year is your truck? { I am asking slc10844 this question} and what synthetic oil are you using. thanks for your input.

 

CI-4 is the new standard. You can go up (CH-4 to CI-4) from the manufactures recommendation, but you can't go down (CI-4 to CH-4). The 6.0 recommendation is CI-4. The 7.3 can use either one. I use Rotella T Full Synthetic 5w-40. I use it year round with a 5000 mile oil change schedule in my 03, 7.3.