6.0 PowerStroke bulletins
6.0 Oil Recommendations:
Some trucks with the 6.0 may exhibit hard starting, rough running and lack of power in cold temperatures, particularly on a cold start. This may be due to the oil being to thick for the operating conditions. Ford is recommending to use the following oils for the listed operating temperature.
SAE 15W-40 is the preferred oil above 30 degrees, but it is acceptable for use down to 10 degrees, and is recommended for towing down to this temperature.
SAE 10W-30 is the preferred weight between -10 to 30 degrees.
SAE 5W-30 and 5W-40 is acceptable for use below 30 degrees, and 0W-30 is acceptable below zero.
(All temperatures are in Fahrenheit.)
The oil used should meet Ford's specification of WSS-M2C171-D or API CI-4 PLUS, CI-4/SL or DHD-1. CH-4 is acceptable for use if CI-4 PLUS is not available. TSB #05-16-6.
Keep in mind that CI-4 oil is designed for the increased soot contamination and higher coolant temperatures of cooled EGR systems on a diesel; CH-4 is not.
Nowhere does the TSB mention synthetic versus conventional oil recomendations or ranges.
Ford has not released anything recommending NOT to use a specific brand of oil.