MIL-PRF-46170: Rust-Inhibited, Fire-Resistant Hydraulic Fluid for Ground Equipment

MIL-PRF-46170 is the U.S. military specification for a rust-inhibited, fire-resistant, synthetic hydrocarbon hydraulic fluid for ground vehicles, ordnance recoil mechanisms and preservation of hydraulic systems. It is the Army’s fire-resistant counterpart of MIL-PRF-6083. Castrol’s data sheet says it “is intended for use as a direct replacement for MIL-PRF-6083”. NATO code H-544, military symbol FRH. The current revision found is MIL-PRF-46170E (30 May 2013), which supersedes revision D (20 July 2004). Only one type remains: Type I, undyed.

What the specification says it is for. Scope (section 1.1): use from −40 °C to 200 °C (−40 °F to 392 °F) in recoil mechanisms and ground vehicle and equipment hydraulic systems. Section 6.1 adds that the fluid is rust inhibited and may be used as a preservative medium for hydraulic systems and components. The specification also says the fluid will not be used for aircraft systems, aircraft ground support equipment or the preservation of aircraft components. The manufacturers describe it more widely: Shell sells AeroShell Fluid 61 as a fire-resistant preservative grade fluid, and Castrol calls Brayco Micronic 883 a fluid “for aircraft, ordnance and industrial use”. Check the equipment manual before you use it in an aircraft.

Fire resistance and cold flow. The fluid must have a flash point of at least 218 °C, a fire point of at least 246 °C and an autoignition temperature of at least 343 °C. The −40 °C viscosity limit is 2600 mm²/s and the pour point limit is −54 °C. The spec says it mixes with MIL-PRF-5606, MIL-PRF-6083, MIL-PRF-83282 and MIL-PRF-87257 fluids at all concentrations from −40 °C to 135 °C. Viscosity index improvers and pour point depressants are not allowed. Compare MIL-PRF-83282 (aircraft fire-resistant fluid) and MIL-PRF-5606 (petroleum aircraft fluid).

What this site has for it. Only viscosity data against temperature, from manufacturer data sheets (single-lot typical values, not measurements). The sheets give density at 15.6 °C only. No source found gives density at other temperatures, specific heat or thermal conductivity, so there are no pages for those properties or for Prandtl number, thermal diffusivity or thermal expansion.

MIL-PRF-46170 Property Calculators

Explore the MIL-PRF-46170 property calculator on KasperCalc. For related fluids, see MIL-PRF-83282 General Properties, MIL-PRF-6083 General Properties and MIL-PRF-5606 General Properties.

Kinematic Viscosity
Specifications
DesignationStatus / Source
MIL-PRF-46170EPerformance Specification: Hydraulic Fluid, Rust Inhibited, Fire Resistant, Synthetic Hydrocarbon Base, NATO Code No. H-544. Dated 30 May 2013; supersedes MIL-PRF-46170D of 20 July 2004. Prepared by U.S. Army TARDEC (EverySpec copy, read in full). A Notice 1 (validation, 2018) exists and was not opened
MIL-PRF-46170D / C, MIL-H-46170BEarlier revisions. Revision C had a Type II (dyed red) that is “no longer available”. The AeroShell Book sheet on this page is printed against revision D. Not opened except through those sheets and the 1989 Army report below
QPL-46170The Qualified Products List for the specification exists. It was not opened, so it is not reproduced here

NATO code H-544 and military symbol FRH are printed in the specification. The U.S. Army Belvoir report 2482 (1989) describes MIL-H-46170 (FRH) as the rust-inhibited, fire-resistant fluid that was partly adopted to replace MIL-H-6083 (OHT) in Army vehicles.

Common Products with MIL-PRF-46170 Data Sheets
ProductClaim as stated on the data sheetData sheet
Castrol Brayco Micronic 883“meets and is qualified under military specification MIL-PRF-46170E, Type I, Amendment 2” (sheet dated 10 June 2021)Castrol data sheet
AeroShell Fluid 61“MIL-PRF-46170E Type I”, NATO Code H-544 (Shell TDS v1.4, 31 May 2021). The older AeroShell Book sheet says “Approved MIL-PRF-46170D Type I”Shell TDS (reseller copy); AeroShell Book pages (reseller copy)
RADCOLUBE FR170 (Radco)Titled “MIL-PRF-46170E”; NATO Code H-544; qualification numbers HF-78, HF-79, HF-80, HF-82, HF-83, qualification dates 17 May 2019 to 20 July 2021Radco data sheet (reseller copy)

Products are listed because their data sheets were opened for this page; this is not a Qualified Products List. Claim wording is as printed on each sheet. Other products are sold against the same specification (for example NYCO Hydraunycoil FH 3) but no maker data sheet with values was available, so they are not listed. Royco 756 and Hydraunycoil FH 2 are not 46170 fluids: Royco 756 is a MIL-PRF-5606 fluid and FH 2 is sold against MIL-PRF-83282.

Manufacturer Typical Values (not measurements)
PropertyBrayco Micronic 883 (46170E, 2021)AeroShell Fluid 61 (46170E, 2021)AeroShell Fluid 61 (46170D, Book)RADCOLUBE FR170 (46170E)
Relative density (specific gravity) at 15.6 °C (60 °F)0.85 (7.08 lb/gal)0.8540.8590.848
Kinematic viscosity, −54 °C (−65 °F), mm²/s14,650—15,022—
Kinematic viscosity, −40 °C (−40 °F), mm²/s2,4502,3042,4882,047
Kinematic viscosity, 40 °C (104 °F), mm²/s15.614.815.4314.7
Kinematic viscosity, 100 °C (212 °F), mm²/s3.73.63.713.67
Kinematic viscosity, 204 °C (400 °F), mm²/s1.15———
Viscosity index126———
Flash point (°C)226 (COC)221233 (COC)222
Fire point (°C)252 (COC)251248248
Autoignition temperature (°C)380377354378
Pour point (°C)−60below −69below −54−72
Acid number (mg KOH/g)0.040.170.070.17
Evaporation loss, 22 h at 149 °C (%)—42.391.70
Rubber swell, NBR-L, 168 h at 70 °C (%)1715.821.515.2
Isothermal secant bulk modulus1,510 MPa (219,000 psi) at 37.8 °C, 4000 psi——1,760 MPa at 40 °C, 27.6 MPa

Single-lot typical values from the manufacturer data sheets, not measurements made for this site, with no stated uncertainty. “—” means the sheet does not print the value. Castrol prints the −54 °C row as “−54 °C / 65 °F”; the Fahrenheit value is a typo for −65 °F. Castrol’s bulk modulus is printed in psi (the units column wrongly says “minutes”) and is shown here converted to MPa (219,000 psi = 1,510 MPa). The two bulk moduli differ by 14 % (two products, two labs, 37.8 against 40 °C). The AeroShell sheets say typical values are of current production and may vary. Test methods differ between sheets (for example Cleveland Open Cup on the Castrol and Book sheets).

Specification Limits: MIL-PRF-46170E
PropertyTempMIL-PRF-46170E limitSource
Kinematic viscosity, max−40 °C2,600 mm²/sMIL-PRF-46170E Table I, p.7
Kinematic viscosity, max40 °C19.5 mm²/sMIL-PRF-46170E Table I, p.7
Kinematic viscosity, min100 °C3.4 mm²/sMIL-PRF-46170E Table I, p.7
Flash point, min—218 °C (ASTM D92)Table I, p.6
Fire point, min—246 °C (ASTM D92)Table I, p.6
Autoignition temperature, min—343 °C (ASTM E659)Table I, p.6
Pour point, max—−54 °CTable I, p.7
Acid number, max—0.20 mg KOH/gTable I, p.6
Evaporation loss, max149 °C, 22 h5 % by weightTable I, p.6
Isothermal secant bulk modulus, min40 °C1,379 MPa (200,000 psi) at 27.6 MPa (4000 psig), ASTM D6793Table I, p.6
Linear flame propagation rate, max—0.30 cm/sTable I, p.6
Foaming tendency, max24 / 94 / 24 °C65 mL after 5 min blowing; stability 0 mL after 10 minTable I, p.6
Swelling of NBR-L rubber70 °C, 168 h15.0 to 25.0 %Table I, p.7
Steel-on-steel wear, max scar diameter—0.30 mm (147 N), 0.65 mm (392 N)Table I, p.7
Water, max—0.05 % by massTable I, p.7
Relative density at 15.6/15.6 °C (60/60 °F)15.6 °Cno limit; reported at qualification, and later lots must be within ±0.008 of itTable I, p.7 and section 3.4.7
Operating temperature range—−40 °C to 200 °CScope 1.1, p.1
Prohibited additives—pour point depressants and viscosity index improversSection 3.3

Limits are from MIL-PRF-46170E (30 May 2013). The specification has no requirement for specific heat, thermal conductivity or density against temperature. Notice 1 (2018) was not opened and may be a later status of revision E. Particle-count, corrosion, oxidation-stability and low-temperature-stability tests are listed in Table I and not repeated here.

MIL-PRF-46170 vs MIL-PRF-83282: Specification Limits
PropertyMIL-PRF-46170E (Table I)MIL-PRF-83282D (Table II)MIL-PRF-83282 typical (ROYCO 782 / AeroShell 31 / RADCOLUBE FR282)
Kinematic viscosity, 100 °C (mm²/s)3.4 min3.45 min3.51 / 3.53 / 3.63
Kinematic viscosity, 40 °C (mm²/s)19.5 max14.0 min14.2 / 14.3 / 15.0
Kinematic viscosity, −40 °C (mm²/s)2,600 max2,200 max2027 / 2059 / 2089
Flash point (°C)218 min205 min218 / 218 / 221 (ASTM D92)
Fire point (°C)246 min245 min251 / 251 / 251
Autoignition temperature (°C)343 min345 minRADCOLUBE FR282: 370 (ASTM E659)
Pour point (°C)−54 max−55 max−61 / −69 / −69
Bulk modulus, isothermal secant, 40 °C (MPa)1,379 min (at 27.6 MPa)1,379 min (0 to 69 MPa)RADCOLUBE FR282: 1,693
Operating range (°C)−40 to +200−40 to +205—
Intended useGround vehicles, recoil mechanisms, preservationAircraft and missile hydraulic systems—

MIL-PRF-83282D values and the 83282 typical values are copied unchanged from MIL-PRF-83282 General Properties, which names their sources. The two specifications may use different test methods and conditions (for example for bulk modulus pressure), so some rows are not strictly like-for-like. See also MIL-PRF-46170 viscosity and MIL-PRF-83282 viscosity.

Sources
  • US Department of Defense, MIL-PRF-46170E, Performance Specification: Hydraulic Fluid, Rust Inhibited, Fire Resistant, Synthetic Hydrocarbon Base, NATO Code No. H-544, 30 May 2013. everyspec.com. Scope, sections 3.3, 3.4.1, 3.4.7, 6.1, Table I (pp.6–7). Accessed 29 Oct 2026.
  • Castrol, Brayco Micronic 883 Product Data, 10 Jun 2021. Brayco Micronic 883 data sheet (hosted copy of the maker’s PDF). Typical values, bulk modulus and qualification claim. Accessed 29 Oct 2026.
  • Shell, AeroShell Fluid 61 (NA) Technical Data Sheet, v1.4, 31 May 2021. AeroShell Fluid 61 TDS (reseller copy). Typical values and specification list. Accessed 29 Oct 2026.
  • Shell, The AeroShell Book, hydraulic fluids pp. 6.24 to 6.27, AeroShell Fluid 61. AeroShell Fluid 61 (AeroShell Book pages) (reseller copy; edition year not printed). Typical values against MIL-PRF-46170D. Accessed 29 Oct 2026.
  • Radco Industries, RADCOLUBE FR170 data sheet (MIL-PRF-46170E). RADCOLUBE FR170 data sheet (reseller copy). Typical values and qualification details. Accessed 29 Oct 2026.
  • C. Van Brocklin, Single Hydraulic Fluid for Army Ground Combat and Tactical Vehicles and Equipment, Report 2482, U.S. Army Belvoir RD&E Center, August 1989. DTIC ADA212596. apps.dtic.mil/sti/tr/pdf/ADA212596.pdf. Background on the Army use of MIL-H-46170 (no property values taken from it).
  • MIL-PRF-83282D values and typicals: see the sources on MIL-PRF-83282 General Properties.

All 46170 property values are manufacturer single-lot typicals or specification limits. None is a measurement made for this site, and none has a stated uncertainty. Searches of DTIC, NIST and manufacturer sites found no source for density against temperature, specific heat or thermal conductivity of MIL-PRF-46170 fluid. Data are also listed in tools/mil-prf-46170-sources.json and tools/mil-prf-46170-derived.json.

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