MIL-PRF-6083 Rust-Inhibited Petroleum Hydraulic Fluid

MIL-PRF-6083 is a rust-inhibited petroleum (mineral oil) hydraulic fluid for preservation and operation, Military Symbol OHT, NATO code C-635, used from −54 °C to +135 °C (−65 °F to 275 °F). The current specification is MIL-PRF-6083G (26 April 2013), which supersedes MIL-PRF-6083F. It is used both as a preservative in hydraulic systems and components and as the working fluid. The specification says it is not to be used in aircraft systems, aircraft ground support equipment or for preserving aircraft components, and that it is intended for operation where corrosion protection is needed and MIL-PRF-46170 fluid cannot be used (for example recoil mechanisms and hydraulic systems for rotating weapons or aiming devices of tactical and support ordnance equipment).

How it relates to the other military hydraulic fluids. MIL-PRF-5606 is the plain petroleum aircraft, missile and ordnance fluid. A 1975 Army report describes MIL-H-6083 as essentially MIL-H-5606 with a rust preventative added. MIL-PRF-6083G says the two are miscible in all proportions from −54 °C to 135 °C, and the same is stated for MIL-PRF-83282, MIL-PRF-46170 and MIL-PRF-87257. It is still not a substitute for any of them. MIL-PRF-46170 is the rust-inhibited fire-resistant synthetic hydrocarbon fluid that the Army developed to replace 6083, because the petroleum fluid is flammable.

What data this site has. There is a kinematic viscosity calculator and chart, built from four manufacturer data sheets and the specification limits. There are no density, specific heat, thermal conductivity, thermal expansion or vapor pressure values for MIL-PRF-6083 versus temperature in any primary source found (specification, government reports, data sheets). So there are no pages for those properties, and no dynamic viscosity, Prandtl number or thermal diffusivity (each needs them). Nothing here is borrowed from MIL-PRF-5606. The only density data are single specific gravity values at 15.6 °C, listed below. Manufacturer values are single-lot typicals and are labelled as such.

Specifications
DesignationStatus / Source
MIL-PRF-6083GPerformance Specification: Hydraulic Fluid, Petroleum Base, for Preservation and Operation. 26 April 2013, supersedes MIL-PRF-6083F (EverySpec copy, read in full). Military Symbol OHT, NATO C-635. A Notice 1 dated 27 Feb 2018 exists and was not opened
MIL-PRF-6083FSuperseded by 6083G. Not opened. The 2009 Castrol Brayco Micronic 783 data sheet cites this revision and lists older viscosity limits (see the viscosity page)
MIL-H-6083Older designation (before the MIL-PRF format), listed in 1975–1989 Army reports. Spec revisions of that era are not covered here
NATO C-635 / OHTIdentification of the fluid in MIL-PRF-6083G (1.1 and 3.6)

Other national designations are not stated in the sources used here and are not listed.

Common Products with MIL-PRF-6083 Data Sheets
ProductClaim as stated on the data sheetData sheet
RADCOLUBE RHP6083 (Radco Industries)MIL-PRF-6083G; NATO Code C-635; Qualification Numbers H-6067 and H-6068 (qualified 19 Feb and 25 Aug 2020). The 2025 sheet is titled “MIL-PRF-6083G Hydraulic Fluid, Petroleum Base, Preservation and Operation”TDS 2025-08-15; earlier sheet
Castrol Brayco Micronic 783“meets the requirements of and is qualified to MIL-PRF-6083F”; P-15 preservative under MIL-P-116; Military Symbol OHT; NATO Code C-635 (sheet dated 16 July 2009)Brayco-Micronic-783-pds.pdf
ROYCO 783 (LANXESS)“meets the requirements of and is qualified to MIL-SPEC: MIL-PRF-6083, NATO Code Number C-635” (technical information effective 26 May 2016)LANXESS_ROYCO_783_EMEA_EN.pdf

Only products whose data sheet was opened are listed, with the claim as printed. A data sheet claim is not a qualification record. Check the current Qualified Products List and the product’s own sheet before you buy or specify.

Specification Limits — MIL-PRF-6083G Table I
Property (test)LimitCompare MIL-PRF-5606H
Kinematic viscosity at −54 °C (−65 °F), mm²/s (ASTM D445)3300 max2500 max
Kinematic viscosity at −40 °C (−40 °F), mm²/s700 max600 max
Kinematic viscosity at 40 °C (104 °F), mm²/s13.2 min13.2 min
Kinematic viscosity at 100 °C (212 °F), mm²/s4.6 min4.90 min
Flash point (ASTM D93)82 °C (180 °F) min82 °C min
Pour point (ASTM D97)−59 °C (−74 °F) max−60 °C max
Isothermal secant bulk modulus at 40 °C and 27.6 MPa (4000 psig) (ASTM D6793)1379 MPa (200,000 psi) min1379 MPa min
Water (ASTM D6304)0.05 mass % max (500 ppm)100 ppm max
Evaporation loss, 22 h at 100 °C (ASTM D972)75 % by weight maxdifferent test conditions, not compared
Trace sediment (ASTM D2273)0.005 mL max—
Rubber swell, NBR-L, 168 h at 70 °C (ASTM D4289)19.0 to 31.0 %—
Operating temperature range−54 to +135 °C (−65 to 275 °F)−54 to +135 °C
Density, specific gravity, specific heat, thermal conductivity, expansionNo requirementNo finished-fluid density limit

6083G limits are from Table I (printed pages 5 and 6) and clause 1.1. The 5606H column is copied from the MIL-PRF-5606 general page (MIL-PRF-5606H Tables I and II) for comparison; the water conversion to ppm is a unit conversion only. These are acceptance limits, not measurements.

Specific Gravity Values (single temperature)
Product (data sheet)Printed valueSpecific gravity, 15.6 °C / 15.6 °CBasis
RADCOLUBE RHP6083, 2025 sheetAPI gravity 30.4 (ASTM D1298)0.874Computed here: 141.5 / (131.5 + API). Typical
RADCOLUBE RHP6083, 2020 sheetAPI gravity 33.40.858Computed here from API. Typical, older lot
Castrol Brayco Micronic 783, 2009 sheetSpecific gravity 0.88; density 7.32 lb/gal at 60 °F; API gravity 29.50.88As printed. 7.32 lb/gal is about 0.877 and API 29.5 is about 0.879, so the sheet’s own entries differ by about 0.002
ROYCO 783, 2016 sheetSpecific gravity 0.8755 at 15.6 °C (ASTM D1298)0.8755As printed. Typical
RADCOLUBE RHP6083 safety data sheet, 2025Density 0.866 to 0.8874 at 15.6 °C (water = 1)0.866 to 0.8874A range, not a typical value

These are the only density values found for MIL-PRF-6083. They are single-lot manufacturer values at one temperature, so there is no density-versus-temperature page. The spread between lots (0.858 to 0.879) is larger than the change of density over about 25 °C, so do not use one lot’s value to correct another.

Manufacturer Typical Values (not measurements)
SourcePropertyTypical value
RADCOLUBE RHP6083, 2025 sheetKinematic viscosity (ASTM D445, mm²/s)2859 @ −54 °C; 559 @ −40 °C; 15.6 @ 40 °C; 5.45 @ 100 °C
RADCOLUBE RHP6083, 2025 sheetIsothermal secant bulk modulus, 40 °C, 4000 psig (ASTM D6793)1606 MPa (232,931 psi)
RADCOLUBE RHP6083, 2025 sheetPour point (ASTM D97)below −72 °C
RADCOLUBE RHP6083, 2020 sheetKinematic viscosity (mm²/s)2916 @ −54 °C; 600 @ −40 °C; 15.4 @ 40 °C; 5.5 @ 100 °C
RADCOLUBE RHP6083, 2020 sheetIsothermal secant bulk modulus, 40 °C, 4000 psig227,286 psi (1567 MPa)
RADCOLUBE RHP6083, 2020 sheetFlash point (ASTM D93) / pour point83 °C / −69 °C
RADCOLUBE RHP6083 safety data sheet, 2025Flash point (ASTM D93); kinematic viscosity at 40 °C84 to 94 °C; 13.2 to 17.3 mm²/s (ranges)
Castrol Brayco Micronic 783, 2009Kinematic viscosity (mm²/s)3450 @ −54 °C; 650 @ −40 °C; 13.6 @ 40 °C; 4.7 @ 100 °C
Castrol Brayco Micronic 783, 2009Flash point, PMCC (ASTM D93)100 °C (212 °F)
Castrol Brayco Micronic 783, 2009Pour point (ASTM D97)−65 °C (−85 °F)
Castrol Brayco Micronic 783, 2009Viscosity index (ASTM D2270)291
ROYCO 783, 2016Kinematic viscosity (mm²/s)3100 @ −54 °C; 685 @ −40 °C; 13.8 @ 40 °C (no 100 °C value)
ROYCO 783, 2016Flash point (ASTM D92) / pour point105 °C (221 °F) / −66 °C (−86 °F)

Single-lot typical values from manufacturer data sheets for products sold against the specification; they are not measurements made for this site and carry no stated uncertainty. The four lots differ noticeably in viscosity. The Brayco sheet is from 2009 and cites 6083F. The flash and pour point values use different ASTM methods on different sheets (D92 and D93).

MIL-PRF-6083 Property Calculators

The MIL-PRF-6083 property calculator on KasperCalc:

Kinematic Viscosity

Related fluids:

MIL-PRF-5606 MIL-PRF-83282 MIL-PRF-46170
Sources
  • US Department of Defense, MIL-PRF-6083G, Performance Specification: Hydraulic Fluid, Petroleum Base, for Preservation and Operation, 26 April 2013. everyspec.com. Clauses 1.1, 3.4.3 and 6.1; Table I (pp.5–6). Accessed 29 Oct 2026.
  • Radco Industries, Technical Data Sheet for RADCOLUBE RHP6083, MIL-PRF-6083G, product code 23271-G, 15 Aug 2025. radcoind.com TDS. Typical results.
  • Radco Industries, RADCOLUBE RHP6083 Hydraulic Fluid, MIL-PRF-6083G data sheet (undated, qualified 2020). data sheet (Petroleum Service Company copy). Typical results.
  • Radco Industries, RADCOLUBE RHP6083 Safety Data Sheet, 15 Aug 2025. radcoind.com SDS. Density, flash point and viscosity ranges (section 9).
  • Castrol, Brayco Micronic 783 Product Data, 16 July 2009, Version 1. Brayco Micronic 783 data sheet. Typical characteristics.
  • LANXESS, ROYCO 783 Preservative Mineral Hydraulic Fluid, Data Sheet, effective 26 May 2016. ROYCO 783 data sheet. Typical properties.
  • B. R. Wright, W. D. Weatherford Jr. and M. E. Le Pera, Investigation of the Flammability Properties of Hydraulic Fluids, AFLRL No. 70, US Army Fuels and Lubricants Research Laboratory, June 1975. DTIC ADA019775. apps.dtic.mil/sti/tr/pdf/ADA019775.pdf. Statement that MIL-H-6083 is essentially MIL-H-5606 with a rust preventative added. No property data used.
  • US Department of Defense, MIL-PRF-5606H, 7 June 2002. everyspec.com. Comparison column of limits only, as on the MIL-PRF-5606 general page.

Manufacturer values are single-lot typicals with no stated uncertainty. No primary source with density, specific heat, thermal conductivity, expansion or vapor pressure versus temperature for MIL-PRF-6083 was found. MIL-PRF-6083F and earlier, and SAE AIR1362 (paywalled), were not opened.

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