Castrol CRB Monograde 30 CF is a diesel engine oil designed for use in heavy duty diesel engines, hydraulic systems and transmissions that specify the use of monograde diesel engine oil. Advantages During its working life, your engine faces challenges from combustion by-products that can form deposits, and thicken the oil. Castrol CRB Monograde 30 CF combats these issues in two ways: It contains cleaning agents which displace particles that may otherwise build up on your engine surfaces reducing deposits. 1. 2. It also contains anti-oxidants which disrupt the chemical reactions that can lead to oil thickening. Castrol CRB Monograde 30 CF provides protection across multiple applications to encourage long and healthy engine life.