ISO 3448

ISO VG 320 at temperature

ISO VG 320 is one preferred-number step above 220. The midpoint is 320 mm²/s at 40°C, and the window is 288 to 352. That step changes the film and the churning loss. It is not a label change.

The ISO 3448 window at 40°C is 288 to 352 mm²/s. The midpoint used below is 320.

Slower enclosed drives, heavily loaded conveyors, and gearboxes that live in warm rooms are where 320 EP gear oil is ordinary. Moving from 220 to 320 because the last fill was noisy, without a temperature or a pitch-line velocity, is how sumps get hot and seals get pushed.

The 100°C figures on this page are illustrative. ISO 3448 specifies the grade at 40°C only. Each column is the viscosity of an oil that hits the grade midpoint at 40°C and the stated viscosity index, solved with ASTM D2270, then moved to other temperatures with the ASTM D341 Walther equation (constant 0.7). A dash means that viscosity index would put the oil below 2 mm²/s at 100°C, where ASTM D2270 does not define VI. Use the data sheet in the converter when you have one.

Put the data sheet’s own 40°C and 100°C numbers into the two-point calculator. The viscosity index of those two points is explained on the viscosity index page.

Where this grade shows up

Use 320 when the OEM plate says 320, or when the AGMA 9005 pitch-line-velocity method lands there at your bulk oil temperature. The steps of that method, without the copyrighted chart, are on the industrial gearbox page. If the box is a worm gear, read worm gear oil before you treat 320 as heavy enough.

Compare branded products on oilviscositychart.com. The other heavy grades are ISO VG 220 and ISO VG 460.

Questions

What is the ISO VG 320 range?

288 to 352 mm²/s at 40°C. Midpoint 320 mm²/s. ISO 3448.

Is ISO VG 320 the same as SAE 90?

No. ISO VG 320 is a 40°C kinematic window. SAE 90 is a 100°C gear-oil window, 13.5 to less than 18.5 mm²/s, from SAE J306. A VG 320 oil can land in or out of SAE 90 depending on its viscosity index.