KasperCalc: MIL-PRF-5606 General Properties

MIL-PRF-5606 as an Aircraft Hydraulic Fluid

MIL-PRF-5606 is the U.S. military performance specification for petroleum-base hydraulic fluid for aircraft, missile and ordnance systems. The fluid is a mineral-oil product dyed red, and the specification (MIL-PRF-5606H, 7 June 2002) supersedes MIL-H-5606G, the designation under which the fluid is also widely known. MIL-PRF-5606H gives an operating temperature range of −54 °C to +135 °C and is marked inactive for new design.

The measured properties on this page are the MIL-H-5606 columns of NADC-79248-60 (Conte & Hammond, Naval Air Development Center, 1980, DTIC ADA081597), which predates the MIL-PRF designation, does not state the specification revision or lot tested, and gives no measurement uncertainty. Manufacturer values are single-lot typicals and are labelled as such. MIL-PRF-5606 is a petroleum (mineral oil) hydraulic fluid; MIL-PRF-23699 is a synthetic ester turbine engine oil, and its values are shown beside the 5606 values for comparison.

MIL-PRF-5606 All-Properties Calculator

Degrees (°F):

Degrees (°C):

Density

Density (kg/m³):

Density (lb/gal):

Density (lb/ft³):

Specific Gravity:*

Viscosity

Kinematic Viscosity (mm²/s):

Kinematic Viscosity (SSU):

Dynamic Viscosity (mPa·s):

Dynamic Viscosity (lb/(ft·s)):

Thermal Properties

Specific Heat (kJ/kg·K):

Specific Heat (BTU/(lb·°F)):

Thermal Conductivity (W/m·K):

Thermal Conductivity (BTU/(hr·ft·°F)):

Thermal Conductivity (BTU·in/(hr·ft²·°F)):

Thermal Diffusivity (×10⁻⁸ m²/s):

Prandtl Number:

Thermal Expansion

β × 10⁻⁴ (1/K):

*Specific gravity is referenced to a static water density of 998 kg/m³ (water at 60 °F) rather than to water at the fluid's own temperature.

Combines the Density, Viscosity, Specific Heat, Thermal Conductivity, Thermal Diffusivity, Prandtl Number, and Thermal Expansion calculators into one temperature lookup, atmospheric pressure. All values come from fits to NADC-79248-60 (MIL-H-5606): density 38–204 °C, specific heat and thermal conductivity −18 to 204 °C, kinematic viscosity −54 to 204 °C (the −40 to 38 °C span is interpolation only). Dynamic viscosity, diffusivity, Prandtl number and expansion are derived from density and are limited to 38–204 °C.

Specifications

Designation	Status / Source
MIL-PRF-5606H	Performance Specification: Hydraulic Fluid, Petroleum Base; Aircraft, Missile, and Ordnance. Base document of 7 June 2002; marked inactive for new design (EverySpec copy)
MIL-PRF-5606J	Referenced by the NYCO Hydraunycoil FH 51 data sheet (approved MIL-PRF-5606 J), which shows the viscosity, pour point, flash point, acid number and evaporation limits unchanged from H. Revision J itself was not opened
MIL-H-5606G	Superseded by MIL-PRF-5606H (per the H document)
MIL-H-5606	Designation of the fluid tested in NADC-79248-60 (1980); the specification revision is not stated in the report

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

Common Products with MIL-PRF-5606 Data Sheets

Product	Claim as stated on the data sheet	Data sheet
NYCO Hydraunycoil FH 51	Approved MIL-PRF-5606 J	FH51TDS.pdf
ROYCO 756 / 756A	756: qualified under MIL-PRF-5606H(3); 756A column is Mil-H-5606A level	LANXESS data sheet
Mobil Aero HF Series (HF, HFA)	Properties table showing MIL-PRF-5606 limits in parentheses	mobil.com product page
Chemsol	“U.S. Approved: MIL-PRF-5606H” (distributor typical sheet)	Chemsol TDS
Chevron Hydraulic Oil 5606	Claimed to meet MIL-PRF-5606H and MIL-H-5606G; general-purpose industrial/marine oil	Chevron PDS

Products are listed because they have a data sheet in the sources used; this is not a Qualified Products List. Approval wording is as printed on each sheet.

Properties at Measured Temperatures — NADC-79248-60

Property	38 °C (100 °F)	93 °C (200 °F)	149 °C (300 °F)	204 °C (400 °F)	Source
Density (kg/m³)	843	802	764	724	NADC Table 2
Kinematic viscosity (mm²/s)	14.2	5.4	2.9	1.9	NADC Table 1
Dynamic viscosity (mPa·s)	11.971	4.331	2.216	1.376	Derived: Table 1 × Table 2
Specific heat (kJ/(kg·K))	1.944	2.195	2.425	2.676	NADC Table 7
Thermal conductivity (W/(m·K))	0.135	0.131	0.126	0.123	NADC Table 8
Thermal diffusivity (×10⁻⁸ m²/s)	8.2378	7.4415	6.8009	6.3486	Derived: k/(ρ·c_p)
Prandtl number	172.4	72.6	42.6	29.9	Derived: μ·c_p/k
β (×10⁻⁴ 1/K)	8.4631	8.8763	9.3406	9.8464	Derived: from Table 2 linear fit

Measured MIL-H-5606 values, atmospheric pressure. Density, kinematic viscosity, specific heat and thermal conductivity are NADC-79248-60 Tables 2, 1, 7 and 8 (the report lists 100, 200, 300 and 400 °F as 38, 93, 149 and 204 °C). Dynamic viscosity, thermal diffusivity, Prandtl number and thermal expansion coefficient are derived from those tables; β = −(1/ρ) dρ/dT from the straight-line fit ρ = 869.517 − 0.71295 T_°C kg/m³. The report states an average cubical expansion of 8.6×10⁻⁴ 1/°C over 38–149 °C (p.15) as a cross-check. Specific heat is given in the report in J/(kg·K); it is shown here in kJ/(kg·K) to match the MIL-PRF-23699 page. Method, lot and uncertainty are not given in the report.

Specification Limits — MIL-PRF-5606H

Property	Temp	MIL-PRF-5606H limit	Source
Kinematic viscosity, max	−54 °C	2500 mm²/s	MIL-PRF-5606H Table II, p.6
Kinematic viscosity, max	−40 °C	600 mm²/s	MIL-PRF-5606H Table II, p.6
Kinematic viscosity, min	40 °C	13.2 mm²/s	MIL-PRF-5606H Table II, p.6
Kinematic viscosity, min	100 °C	4.90 mm²/s	MIL-PRF-5606H Table II, p.6
Flash point, min (finished fluid, ASTM D93)	—	82 °C	MIL-PRF-5606H Table II, p.6; base stock also 82 °C in Table I, p.5
Pour point, max	—	−60 °C	MIL-PRF-5606H Table II p.6; Table I p.5 (base stock)
Acid number, max	—	0.20 mg KOH/g (base stock 0.10)	MIL-PRF-5606H Table II; Table I
Isothermal secant bulk modulus, min	40 °C	1379 MPa (200,000 psi) at 27.6 MPa (4000 psig)	MIL-PRF-5606H Table II; test per 4.4.3.5 and Appendix A
Evaporation loss, max	—	20 %	MIL-PRF-5606H Table II (Royco/Nyco quote 6 h at 71 °C)
Water, max	—	100 ppm	MIL-PRF-5606H Table II
Specific gravity at 15.6/15.6 °C (60/60 °F)	15.6 °C	report only for base stock; sample may not vary more than ±0.008 from the qualification sample; no finished-fluid density limit	MIL-PRF-5606H Table I and footnote, p.5
Change in viscosity at 40 °C after 168 h corrosion/oxidation test	40 °C	−5 to +20 % (row alignment reconstructed from text extraction)	MIL-PRF-5606H Table II
Operating temperature range	—	−54 °C to +135 °C	MIL-PRF-5606H Scope

Limits are from the base MIL-PRF-5606H document (7 June 2002); Amendments 1–3 and revision J were not opened. Nyco’s FH 51 data sheet shows the −54, −40, 40 and 100 °C viscosity limits, pour point, flash point, acid number and evaporation loss unchanged in revision J. Row alignment in the extracted text of Table II was reconstructed for flash point, evaporation loss and the 168 h viscosity-change row.

MIL-PRF-5606 vs MIL-PRF-23699 — Specification Limits

Property	MIL-PRF-5606H (Table II, p.6)	MIL-PRF-23699G Grade STD (spec)	MIL-PRF-23699 typical
Kinematic viscosity, 100 °C (mm²/s)	4.90 min	4.90 to 5.40	5.17
Kinematic viscosity, 40 °C (mm²/s)	13.2 min	23.0 min	25.26
Kinematic viscosity, −40 °C (mm²/s)	600 max	13000 max	8996
Kinematic viscosity, −54 °C (mm²/s)	2500 max	—	—
Flash point (°C)	82 min (ASTM D93)	246 min (Cleveland Open Cup)	256
Pour point (°C)	−60 max	−54 max	<−54
Acid number / total acidity (mg KOH/g)	0.20 max	1 max	0.11
Evaporation loss (%)	20 % max	10.0 max (6.5 hrs @ 204 °C, %m)	3.6

MIL-PRF-23699 values are copied from the MIL-PRF-23699 General Properties page (MIL-PRF-23699G Grade STD / SAE AS5780B Grade SPC table). The two specifications use different test methods for flash point and different conditions for evaporation loss, so those rows are not like-for-like. The remaining 5606H rows (water, bulk modulus, specific gravity, viscosity change, operating range) are in the table above.

MIL-PRF-5606 vs MIL-PRF-23699 — Thermophysical Properties

Property	Temperature	MIL-PRF-5606 (NADC-79248-60)	MIL-PRF-23699	Source
Density (kg/m³)	38 °C (100 °F)	843	978.55	5606: NADC Table 2 23699: NIST IR 8263 Table 23
	93 °C (200 °F)	802	937.08
	149 °C (300 °F)	764	894.85
	204 °C (400 °F)	724	—
Dynamic viscosity (mPa·s)	38 °C (100 °F)	11.971	27.213	5606: Derived: Table 1 × Table 2 23699: NIST IR 8263 Table B4
	93 °C (200 °F)	4.331	5.723
	149 °C (300 °F)	2.216	—
	204 °C (400 °F)	1.376	—
Specific heat (kJ/(kg·K))	38 °C (100 °F)	1.944	1.8345	5606: NADC Table 7 23699: NIST IR 8263 Table 14
	93 °C (200 °F)	2.195	1.9900
	149 °C (300 °F)	2.425	2.1502
	204 °C (400 °F)	2.676	2.3019
Thermal conductivity (W/(m·K))	38 °C (100 °F)	0.135	0.1437	5606: NADC Table 8 23699: NIST IR 8263 Table A4
	93 °C (200 °F)	0.131	0.1359
	149 °C (300 °F)	0.126	0.1269
	204 °C (400 °F)	0.123	0.1175
Thermal diffusivity (×10⁻⁸ m²/s)	38 °C (100 °F)	8.2378	8.007	5606: Derived: k/(ρ·c_p) 23699: Computed on the 23699 page from Tables 23, 14, A4
	93 °C (200 °F)	7.4415	7.287
	149 °C (300 °F)	6.8009	6.594
	204 °C (400 °F)	6.3486	—
Prandtl number	38 °C (100 °F)	172.4	347.333	5606: Derived: μ·c_p/k 23699: Computed on the 23699 page from Tables B4, 14, A4
	93 °C (200 °F)	72.6	83.820
	149 °C (300 °F)	42.6	—
	204 °C (400 °F)	29.9	—
β (×10⁻⁴ 1/K)	38 °C (100 °F)	8.4631	13.8695	5606: Derived: from Table 2 linear fit 23699: NIST IR 8263 Table 23
	93 °C (200 °F)	8.8763	14.4833
	149 °C (300 °F)	9.3406	15.1667
	204 °C (400 °F)	9.8464	—

MIL-PRF-23699 values are what the MIL-PRF-23699 General Properties All-Properties Calculator returns at these temperatures (NIST IR 8263 data, linear interpolation between tabulated points). “—” means the 23699 page has no data at that temperature (density and thermal expansion are valid to 200 °C; dynamic viscosity and Prandtl number to 127 °C). Kinematic viscosity is compared in the specification table above. The two datasets come from different sources, labs and conditions, so small differences should not be over-interpreted.

Bulk Modulus (Isothermal Secant) — NADC Table 3

Pressure	38 °C (100 °F)	93 °C (200 °F)	149 °C (300 °F)	204 °C (400 °F)	Source
Atmospheric	1288	933	676	489	NADC Table 3
20.7 MPaG (3000 psig)	1397	1043	785	599	NADC Table 3
55.2 MPaG (8000 psig)	1580	1225	968	782	NADC Table 3

Bulk modulus in MPa gauge. MIL-PRF-5606H requires a minimum isothermal secant bulk modulus of 1379 MPa (200,000 psi) at 40 °C and 27.6 MPa (4000 psig) (Table II; test per 4.4.3.5 and Appendix A). NADC Tables 4–6 (isothermal tangent, adiabatic secant, adiabatic tangent) have not been transcribed. The MIL-PRF-23699 page has no bulk modulus.

Vapor Pressure — NADC Table 16

Property	38 °C (100 °F)	93 °C (200 °F)	149 °C (300 °F)	204 °C (400 °F)	Source
Vapor pressure (Pa)	13.3	399	5054	27930	NADC Table 16
Vapor pressure (Torr, as printed)	0.1	3	38	210	NADC Table 16

Values appear rounded in the report (13.3 Pa = 0.1 Torr). The MIL-PRF-23699 page has no vapor pressure.

Flash, Fire, Autoignition and Heat of Combustion — NADC Table 10

Property	MIL-H-5606 (measured)	Source
Flash point (ASTM D92)	99 °C (210 °F)	NADC Table 10
Fire point (ASTM D92)	110 °C (230 °F)	NADC Table 10
Autoignition temperature (ASTM D2155)	241 °C (465 °F)	NADC Table 10
Hot manifold drip ignition temperature (FTMS 791b-6053)	560 °C (1040 °F)	NADC Table 10
Heat of combustion (ASTM D240)	42,000,000 J/kg (18,000 BTU/lb)	NADC Table 10 continued, p.41

For comparison, the MIL-PRF-23699 page lists a Cleveland Open Cup flash point specification of 246 °C min and a typical of 256 °C; it gives no fire point, autoignition temperature or heat of combustion.

Manufacturer Typical Values (not measurements)

Source	Property	Typical value
Nyco Hydraunycoil FH 51 TDS	Density	0.87 (units not stated), 20 °C
Nyco Hydraunycoil FH 51 TDS	Kinematic viscosity (ASTM D445, mm²/s)	2012 @ −54 °C; 444 @ −40 °C; 14.12 @ 40 °C; 5.39 @ 100 °C; 2.1 @ 200 °C (as listed in the source data)
Nyco Hydraunycoil FH 51 TDS	Flash point (ASTM D93)	91 °C
Nyco Hydraunycoil FH 51 TDS	Auto-ignition temperature (ASTM E659)	245 °C
Nyco Hydraunycoil FH 51 TDS	Pour point (ASTM D97)	−69 °C
ROYCO 756/756A	Density (ASTM D287)	7.261 lb/gal (756A: 7.26); reference temperature not stated
ROYCO 756/756A	Flash point COC (ASTM D92)	231 °F
ROYCO 756/756A	Pour point (ASTM D97)	−62 °C (756A: −63)
Mobil Aero HF Series	Specific gravity 15.6/15.6 °C (ASTM D4052)	0.872
Mobil Aero HF Series	Kinematic viscosity (mm²/s)	2000 @ −54 °C; 450 @ −40 °C; 14.0 @ 40 °C; 5.2 @ 100 °C
Mobil Aero HF Series	Viscosity index (ASTM D2270)	370
Mobil Aero HF Series	Pour point (ASTM D97)	−62 °C
Mobil Aero HF Series	Flash point	107 °C COC; 96 °C PMCC
Chemsol MIL-PRF-5606H sheet	Specific gravity	0.88 (temperature not stated)
Chemsol MIL-PRF-5606H sheet	Kinematic viscosity (cSt)	1850 @ −54 °C; 451 @ −40 °C; 13.9 @ 40 °C; 5.13 @ 100 °C (labels garbled on sheet; low confidence)
Chevron Hydraulic Oil 5606	Density	0.87 kg/l @ 15 °C
Chevron Hydraulic Oil 5606	Kinematic viscosity (mm²/s)	15.0 @ 40 °C; 5.5 @ 100 °C (viscosity index 300+)

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 ROYCO sheet is headed “typical properties” but its four viscosity entries are the specification limits, so they are not repeated here. Mobil HF-versus-HFA column assignment is unverified. The Chevron product is a general-purpose industrial/marine oil that claims to meet MIL-PRF-5606H and MIL-H-5606G, so it is given low weight. MIL-PRF-23699 typicals appear in the specification comparison above.

MIL-PRF-5606 Property Calculators

Explore the full set of MIL-PRF-5606 property calculators on KasperCalc:

Density Specific Heat Capacity Thermal Conductivity Dynamic and Kinematic Viscosity Prandtl Number Thermal Expansion Coefficient Thermal Diffusivity

Sources

A. A. Conte Jr. and J. L. Hammond, Development of a High Temperature Silicone Base Fire-Resistant Hydraulic Fluid, NADC-79248-60, Naval Air Development Center, Warminster PA, 5 Feb 1980. DTIC ADA081597. apps.dtic.mil/sti/tr/pdf/ADA081597.pdf. Tables 1, 2, 3, 7, 8, 10 and 16 (MIL-H-5606 columns), accessed 12 Oct 2026.
US Department of Defense, MIL-PRF-5606H, Performance Specification: Hydraulic Fluid, Petroleum Base; Aircraft, Missile, and Ordnance, 7 June 2002. everyspec.com. Table II (p.6) and Table I (p.5) limits; scope.
NYCO, Hydraunycoil FH 51 Technical Data Sheet (TDS_FH51-1E11), 2020. aircraftspruce.com/catalog/pdf/FH51TDS.pdf. Typical values.
LANXESS, ROYCO 756/756A Data Sheet, effective 6 Jan 2017. ROYCO 756 data sheet. Typical values.
ExxonMobil, Mobil Aero HF Series product page. mobil.com. Typical values; HF vs HFA column assignment unverified.
Chemsol, U.S. Approved: MIL-PRF-5606H typical properties sheet, July 2011. chemsol.com. Distributor typical sheet; low confidence.
Chevron, Hydraulic Oil 5606 Product Data Sheet, Jan 2024. Chevron PDS. Typical values.
Bruno et al., Thermophysical Properties of Polyol Ester Lubricants, NIST IR 8263, 2019. doi.org/10.6028/NIST.IR.8263. Basis of the MIL-PRF-23699 thermophysical values (Tables 14, 23, A4, B4) on the MIL-PRF-23699 General Properties page.

The NADC report does not state the specification revision or lot of the MIL-H-5606 tested, and gives no measurement uncertainty. Manufacturer values are single-lot typicals.

MIL-PRF-5606 General Properties

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