GPS
castrol.com/GPS
800 255 4417
May 2025
Background & Properties
Industry Specifications
History ................................................................................................. A2
API CK-4 and FA-4 Background ...........................................A3
API CK-4 and FA-4 Engine Tests ...........................................A4
API CK-4 and FA-4 Bench Tests ........................................... A8
Other OEM Specifications...................................................... A12
e API Service Symbol ........................................................... A14
SAE Engine Oil Viscosity Grades
Physical Requirements ............................................................ A15
Comparative Viscosity Classifications ............................ A16
Important Engine Oil Properties
Role of Engine Oil ........................................................................A17
Base Oil ............................................................................................ A18
Base Oil Groups ..........................................................................A20
Base Oil Groups: Characteristics ........................................ A21
Refining Techniques ................................................................. A22
Additives ......................................................................................... A23
Viscosity Index – A Measure of Performance..............A24
A
Engine Oils
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