Motor Oil and Hydraulic Oil by Viscosity Grade

Reading 5W-30: viscosity, base oil and approvals

In 5W-30, the number before the W shows how freely the oil flows when cold, and the second shows its thickness at operating temperature. Use the grade in your manual, because modern engines are built around it. Base oil comes as conventional, synthetic blend or full synthetic, with full synthetic holding up best to heat. Check the service class on the label, and any manufacturer approval your engine requires, not just the viscosity.

Hydraulic oils use a different grading system

Hydraulic oils are sold by ISO viscosity grade such as ISO 32 or ISO 46, a different scale from engine oil grades, so the numbers cannot be compared. Equipment manuals name the grade and whether anti-wear additives are needed. Vegetable-based hydraulic oils are biodegradable and suit sensitive sites, but check seal compatibility before swapping from mineral oil. Jugs and pails are available, and steel reservoirs and replacement spouts support the same equipment.

Questions about Motor Oil and Hydraulic Oil by Viscosity Grade

Can I use 5W-30 in an engine that calls for 5W-20?

It is slightly thicker when hot, and some engines with tight tolerances or variable valve timing are sensitive to that. Use the grade printed on the oil cap or in your manual unless the manual lists both as acceptable.

Is a synthetic blend a true synthetic oil?

No. A blend mixes conventional and synthetic base oils, giving better protection than conventional but less than full synthetic. It sits between the two and is sold for drivers who want some of the benefit.

Can hydraulic oil replace engine oil?

No. Engine oil contains detergents and dispersants that hydraulic oil lacks, and the viscosity systems differ. Each fluid is formulated for its own system, so use only what the equipment or engine manual specifies.