CK-4

Some engine builders like to use API CJ-4 diesel motor oil as a break-in lubricant for new engines. That’s because it contains plenty of zinc (ZDDP) to protect flat-tappet camshafts. Apparently this oil is being replaced with a new formulation, API CK-4 and CK-4/SN (SN means the oil meets current year API standards). And just

The new CK-4 diesel oil specification prompted Ford Motor Co. to issue a technical service bulletin warning Ford owners not to use it in their 6.7-liter diesel engines. The CK-4 diesel specification removed the valvetrain wear test (ASTM-IIIG) used on all previous diesel specifications, like the CJ-4 diesel oil spec. Ford 6.7-liter owners should continue to