Motor oils are typically ________ to _________% base stock.

Motor oils are primarily composed of base stock, which serves as the principal component of the lubricant, providing the necessary viscosity and lubrication properties. The correct range for base stock in motor oil is generally between 75% and 85%. This high percentage ensures that the oil maintains its desired characteristics, including the ability to lubricate engine components effectively, reduce friction, and carry away heat and contaminants.

Base stock can come from various sources, including mineral oils and synthetic formulations, which significantly impact the performance of the motor oil. By having a substantial base stock content, the oil can also accommodate additives, which enhance its performance further in terms of detergency, anti-wear, and oxidation stability. These additives function within the base stock and are added to optimize the oil's performance in various conditions and functionalities.

Other options provided fall outside the typical composition range for most engine oils. The percentages stated would not provide the necessary characteristics expected in a fully formulated motor oil, which is designed to defend against wear, provide high thermal stability, and ensure effective operation under shear and pressure. Thus, the range of 75% to 85% as the base stock concentration highlights the essential balance between base oil and performance-enhancing additives.