Rubia S SAE 40 ni engine oil ya mineral (mono-grade) iliyotengenezwa mahsusi kwa diesel engines, hasa za magari ya zamani, malori, mabasi na mashine za kazi nzito. Ina uwezo mzuri wa kupambana na joto kali, kuzuia uchakavu na kudhibiti uchafu kama sludge na carbon ndani ya engine. Inafaa pia kwa generator na stationary engines, ikihakikisha ulinzi wa muda mrefu na utendaji thabiti kwenye mazingira magumu.