Find my oil

Answer four questions about the gearbox and this page applies ANSI/AGMA 9005-F16 to say which ISO grade and class it needs, then lists the oils in our table that meet it, buy button first. A gearbox maker's own recommendation outranks this; so does an EHL analysis (AGMA 925). The standard says so, and so do we.

1What is it?

Annex B has one set of tables for spur, helical and bevel (B.1 to B.4) and a separate one for worm gears (B.5), which is read from the air temperature rather than the oil's.

2How fast is the slowest gear stage?

Pitch line velocity, m/s

The speed at which the teeth pass each other. Use the final, slowest stage (6113-B16 cl. 11.3.2).

I know the rpm and the gear's pitch diameter instead

v = π × d × rpm / 60000

3How hot does the oil run?

Bulk oil temperature, °C

The sump temperature once the machine has been running a while. Hotter oil is thinner, so a hotter sump asks for a heavier grade.

I only know the air temperature around the gearbox

Annex B assumes the oil runs about 45 °C above ambient. 6113-B16 Table 6 pairs the two the same way. Leave the oil temperature blank and it is derived.

4How cold is the coldest start?

Coldest start-up, °C

The oil must still pour at start. 9005-F16 cl. 7.1.4 wants a pour point at least 5 °C below this, so an oil that never published a pour point is set aside rather than passed. Leave blank if the machine lives indoors and never starts cold.

5Any shock in the drive? (optional)

Driving unit

Driven unit

Annex C Table C.1: any moderate or heavy shock calls for an antiscuff (AS) oil with extreme-pressure additives; uniform on both sides is satisfied by a plain R&O oil. Leave blank to see every class.

6Anything else? (optional)

Bronze or brass in the oil path (worm wheel, bushings): copper strip 1A/1B only

Only oils with a buy button

Flash point at least, °C (the standard's own floor applies anyway)

The result is a link you can send to purchasing.

These annexes are guidelines, and say so. Annex B applies “in the absence of gearbox manufacturer recommendations, specific application standards, or a rigorous EHL analysis”.

Annex B assumes the oil holds its viscosity over the drain interval, and that operating temperature is roughly 45 °C above ambient.
Consult gear, bearing and lubricant suppliers whenever the indicated grade falls below VG 68 or above VG 680.
Above 30 m/s, 9005-F16 refers you to ANSI/AGMA 6011.
Viscosity at temperature is ASTM D341 as set out in AGMA 955-A22 Annex G.3, from the published 40 °C and 100 °C values: a correlation fitted to two points, and below the pour point arithmetic rather than physics.
EHL Film is the oil-only part of the AGMA 925-B22 film-thickness equation (Dowson and Toyoda, cl. 9): viscosity at your operating temperature to the 0.69 power times the pressure-viscosity coefficient to the 0.56 power, the coefficient from 925 Table 4 by base oil type. With the gearbox held constant that is how the oils rank against each other; 1.00 is the thinnest film in the list. It is not an absolute film and not a lambda ratio: those need the gear geometry, the load and the surface finish. Hover a value for the viscosity and coefficient behind it. Polymer-thickened oils shear-thin in the contact and will sit below their number.
h_c, λ and wear risk (when the gear pair is described) are AGMA 925-B22 at the pitch point only: Dowson and Toyoda central film (Eq. 78 to 89), isothermal, with the composite roughness adjusted to the Hertzian width (Eq. 104) and the wear probability from the Figure 19 fits (Eq. 116 to 120). The standard works 25 points along the path of contact and corrects for inlet shear heating; the minimum film is usually a little below the pitch-point value and the heated film lower still (its own Annex D example: 0.24 µm at the pitch point, 0.23 minimum, 0.14 with heating). Tooth temperature is taken as your bulk oil temperature; 925 would add part of the flash rise. The library is checked against Annex D in tests/ehl925-test.php.
Every number here is what the maker published on the datasheet linked on the row. Where a maker published nothing, the oil is set aside and says so, never passed by default.