The present invention relates to a novel gear oil which is useful over a wide variation in temperature, and more particularly pertains to a multi-grade 80W-140 gear-oil composition.

The gear-oil composition of this invention was formulated to meet the minimum 210.degree. F. viscosity of 25 centistokes required for an SAE 140 oil and at the same time to meet the -15.degree. F. maximum viscosity of 150,000 centipoises (Brookfield) required for 80W by SAE J-306a and meeting the -30.degree. F. channel point required for SAE 80 by MIL-L-2105B. Base-stock viscosity should be as high as possible to assure best performance. Oil stocks derived from mid-continent crude oil through distillation into boiling ranges of about 100.degree. F., furfural extraction to 95 V.I., and MEK-toluene solvent dewaxing to 0.degree. F. pour point have been found to be advantageous in meeting the viscometric requirements. A wear additive containing sulfur and phosphorous is usually used for imparting improved extreme pressure, anti-wear, anti-rust and oxidation inhibition to the gear oil. The V.I. improver is an alkyl methacrylate copolymer of relatively specific molecular weight range.

A key to meeting the low-temperature flow requirements without having to alter base-stock composition materially was the discovery of the unexpected beneficial effect of including small amounts (about 0.1 to 1.5%) of dispersant polymer which is preferably an alkyl methacrylate copolymer which has been grafted with a dialkyl amino methacrylate monomer which appears to function as a glass-transition modifier.

A seal-swell agent, which may be a dialkyl ester of phthalic acid, other diesters or an aromatic hydrocarbon mixture, is optionally included in the gear oil of my invention.

The 80W-140 formula of this invention has been extensively tested as a differential lubricant in auto and truck fleets where it has matched or exceeded performance of single-grade SAE 90 oils and SAE 140 oils. The gear oil of this invention has given outstanding performance as a lubricant for worm gears in industrial machines. In the tests with the gear oil of this invention, the oil stayed in grade after prolonged testing in the Vickers pump (ASTM 2882), in the SAE L-37 test, and in the worm gears of industrial machinery.

The composition of the 80W-140 gear oil of my invention falls within the following ranges of ingredients on a volume-percentage basis:

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    Ingredients            Volume %
    ______________________________________
    petroleum-oil stock
     5.0 centistokes at 210.degree. F.
                           23-20
     14.0 centistokes at 210.degree. F.
                           25-24
     25.0 centistokes at 210.degree. F.
                           26-30
    wear additive          5-6
    V.I. improver          16.6-18.6
    dispersant polymer     0.1-1.5
    seal-swell agent       0-2.7
    ______________________________________

    ______________________________________
    Ingredients             Volume %
    ______________________________________
    5.0 centistokes at 210.degree. F. oil
                            23.3
    14.0 centistokes at 210.degree. F. oil
                            25.2
    25.0 centistokes at 210.degree. F. oil
                            25.7
    sulfur-phosphorous wear additive
                            5.5
    V.I. improver (copolymer of
                            16.6
    butyl methacrylate and lower
    level of lauryl methacrylate,
    450,000 weight average molecular
    weight)
    dispersant polymer (copolymer
                            1.0
    of lauryl methacrylate and
    butyl methacrylate grafted
    with dimethyl amino ethyl
    methacrylate)
    seal-swell agent (aromatic
                            2.7
    hydrocarbon mixture,
    B.P. 650.degree.-725.degree. F.)
    ______________________________________

This gear-oil formulation was found to have a viscosity at -15.degree. F. of 138,000 centipoises, a viscosity at 210.degree. F. of 29.04 centistokes and a channel point of -45.degree. F. The base-oil mixture alone for the above formulation had a viscosity at 210.degree. F. of 11.86 centistokes.

The above gear-oil formulation was tested in the differential gear of a passenger automobile and, at the same time, an SAE 90 gear oil was tested in a second automobile and an SAE 140 gear oil was tested in a third automobile. The three test automobiles were driven 40,000 miles, the gear oils were removed and then analyzed for iron by x-ray diffraction analysis. The 80W-140 oil of this invention was found to contain 370 ppm of iron, the SAE 90 gear oil contained 1400 ppm of iron and the SAE 140 gear oil contained 1200 ppm of iron.

An industrial worm-gear test in a hot-wire drawing machine over a period of 10 weeks using the 80W-140 gear-oil formulation of this invention showed that the gear oil suffered relatively no degradation, as demonstrated by the following viscosity and acid numbers:

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    Weeks of Use Viscosity at 210.degree. F.
                                Acid Number
    ______________________________________
    0            28.4           2.99
    2            27.8           3.22
    4            27.7           4.75
    8            25.2           3.69
    10           25.9           3.70
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