Lubrication Questions: Q: What do the numbers and letters in a motor oil designation mean?
• There are several different items encoded. There is a two-letter code indicating the type of detergent package that the manufacturer uses in the oil; this looks like SE,SF,CD or such. The S codes are for gasoline engine applications; the C codes are for diesel engine applications. The second letter is assigned in sequence as new levels of protection are developed; thus SF is considered better than SE, SE is considered better than SD, and so forth.
