MIL-PRF-87252 PAO Coolant Properties & Specs

MIL-PRF-87252 as an Avionics and Radar Coolant

MIL-PRF-87252 is the U.S. military performance specification for a hydrolytically stable, dielectric coolant fluid. The fluid is a synthetic hydrocarbon, normally a hydrogenated polyalphaolefin (PAO) with an oxidation inhibitor, and carries NATO code S-1748. It cools avionics, radar, missile and navigation electronics. The specification (MIL-PRF-87252D, 23 November 2015) covers a −54 °C to +200 °C fluid and supersedes MIL-PRF-87252C with Amendment 1 (29 December 2004). Newer data sheets cite revision E.

About the data: no government report or journal paper with measured MIL-PRF-87252 thermophysical properties was found. The density, specific heat, thermal conductivity and expansion values on these pages are manufacturer typical values from one table (the ROYCO 602 data sheet, identical in the AeroShell Fluid 602 listing). Viscosity values come from four product sheets and the specification limits. The specification sets limits for viscosity, flash and fire point, dielectric strength and other test results. It sets no limit for density, specific heat or thermal conductivity, and only lists informational “typical” values for them in Table III.

Each property is compared with 60/40 ethylene glycol–water by mass, computed with CoolProp 7.2.0 (Melinder 2010 data), from −50 °C to 100 °C only. The glycol mixture carries more heat per kilogram and per litre, but it freezes near −51 °C, it is not a dielectric, and it is far thicker than PAO in the cold. See also ethylene glycol properties.

MIL-PRF-87252 Property Calculators

Explore the full set of MIL-PRF-87252 PAO coolant property calculators on KasperCalc:

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

MIL-PRF-87252 All-Properties Calculator

Degrees (°F):

Degrees (°C):

Density

Density (kg/m³):

Density (lb/gal):

Density (lb/ft³):

Specific Gravity:*

Viscosity

Kinematic Viscosity (mm²/s):

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 Diffusivity (×10⁻⁸ m²/s):

Prandtl Number:

Thermal Expansion

β × 10⁻⁴ (1/K):

Data basis (which values are extrapolated at this temperature)

Density, expansion:

Specific heat, conductivity:

Viscosity:

Dynamic viscosity, Pr, diffusivity:

*Specific gravity here is the density divided by 1000 kg/m³, not corrected for the density of water.

Combines the Density, Viscosity, Specific Heat, Thermal Conductivity, Thermal Diffusivity, Prandtl Number, and Thermal Expansion calculators into one temperature lookup, atmospheric pressure, −54 to 150 °C. All values are fits to manufacturer typical data (ROYCO 602 sheet): density and expansion measured 0–190 °C, specific heat and conductivity measured −17.8 to 260 °C, kinematic viscosity measured −54 to 100 °C (no point between −40 and 40 °C, so that span is interpolation). The “Data basis” rows say where a value is extrapolated. Dynamic viscosity, diffusivity and Prandtl number are measured-range only from 0 to 100 °C.

Specifications

Designation	Status / Source
MIL-PRF-87252D	Performance Specification: Coolant Fluid, Hydrolytically Stable, Dielectric. 23 November 2015, supersedes MIL-PRF-87252C w/Amendment 1 (EverySpec copy; opened and read)
MIL-PRF-87252E	Cited by the RADCOLUBE 500M data sheet (qualified 25 September 2019, AFPET/PTPS 19-014). Revision E itself was not opened; the sheet’s requirement column repeats the D limits
MIL-PRF-87252C	Cited by the ROYCO 602 (2004) and AeroShell Fluid 602 sheets. Superseded by D
MIL-C-87252	Earlier designation (1993), listed as inactive. Not opened
NATO code S-1748	Printed in MIL-PRF-87252D (1.1) and on the AeroShell and Radco sheets

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

Common Products with MIL-PRF-87252 Data Sheets

Product	Claim as stated on the data sheet	Data sheet
ROYCO 602 (LANXESS)	“Royco® 602 is qualified to and meets all requirements of MIL-PRF-87252.” (2020 sheet)	LANXESS data sheet (2020)
ROYCO 602 (ANDEROL, 2004)	“ROYCO 602 is qualified to the current MIL-SPEC revision of MIL-PRF-87252C (USAF).”	ANDEROL data sheet (2004)
AeroShell Fluid 602 (Shell)	Approved MIL-PRF-87252C; NATO code S-1748	AeroShell Book 2003, pp. 240–243
RADCOLUBE 500M (Radco Industries)	MIL-PRF-87252E; Qualification Number AFPET/PTPS 19-014; Qualification Date 25 September 2019	Radco TDS
Castrol Brayco Micronic 889	Sold as a MIL-PRF-87252C dielectric coolant by retailers. Its data sheet could not be opened, so no claim or data is given here	not opened

Products are listed because their data sheets were opened for this page (except Brayco Micronic 889, noted above). This is not a Qualified Products List. The Qualified Products Database is at assist.dla.mil. Approval wording is as printed on each sheet.

Properties vs. Temperature — Manufacturer Typical Values (ROYCO 602)

Temperature	ρ (kg/m³)	ν (mm²/s)	μ (mPa·s)	c_p (kJ/(kg·K))	k (W/(m·K))	α (×10⁻⁸ m²/s)	Pr	β (×10⁻⁴ 1/K)
-54 °C (-65 °F)	840.6*	1087.0	913.697*	1.934*	0.1500*	9.23*	11779*	7.57*
-40 °C (-40 °F)	831.6*	277.0	230.363*	1.982*	0.1486*	9.02*	3072*	7.70*
-20 °C (-4 °F)	818.8*	58.27	47.708*	2.051*	0.1466*	8.73*	667.3*	7.89*
0 °C (32 °F)	805.8	19.95	16.072	2.120	0.1446	8.47	235.6	8.09
20 °C (68 °F)	792.7	9.23	7.320	2.189	0.1426	8.22	112.3	8.29
40 °C (104 °F)	779.5	5.19	4.046	2.258	0.1406	7.99	64.9	8.51
60 °C (140 °F)	766.2	3.30	2.529	2.327	0.1387	7.78	42.4	8.73
80 °C (176 °F)	752.8	2.30	1.734	2.396	0.1367	7.58	30.4	8.96
100 °C (212 °F)	739.2	1.72	1.271	2.464	0.1347	7.39	23.3	9.20
120 °C (248 °F)	725.5	1.35*	0.980*	2.533	0.1327	7.22	18.7*	9.46
150 °C (302 °F)	704.8	1.01*	0.712*	2.637	0.1297	6.98	14.5*	9.86

Fits to the ROYCO 602 typical values, atmospheric pressure. “*” marks extrapolated or derived-from-extrapolated values: density and β below 0 °C; c_p and k below −17.8 °C; ν above 100 °C; μ, α and Pr outside the range where all their inputs are measured. ν is interpolated, not measured, between −40 and 40 °C. μ = ν·ρ; α = k/(ρ·c_p); Pr = μ·c_p/k; β from the density fit.

Specification Limits — MIL-PRF-87252D Table I

Property	Temp	MIL-PRF-87252D limit	Source
Kinematic viscosity, max	−54 °C	1300 mm²/s (initial reading at 1.5 h; also at 3 h and 72 h)	Table I, p.5; 3.3.3, p.4
Kinematic viscosity, max	−40 °C	300 mm²/s	Table I, p.5
Kinematic viscosity, min	40 °C	5.0 mm²/s	Table I, p.5
Kinematic viscosity, min	100 °C	1.65 mm²/s	Table I, p.5
Dielectric strength, min (ASTM D877)	—	35 kV	Table I, p.5
Resistivity, min (ASTM D1169)	25 °C	1.0×10¹⁰ ohm-cm	Table I, p.5
Flash point, min (ASTM D92)	—	150 °C (302 °F)	Table I, p.5
Fire point, min (ASTM D92)	—	160 °C (320 °F)	Table I, p.5
Acid number, max (ASTM D664)	—	0.20 mg KOH/g	Table I, p.5
Water, max (ASTM D6304)	—	50 ppm	Table I, p.5
Rubber swell, NBR-L (ASTM D4289)	70 °C, 168 h	0.0 to +10 % volume	Table I, p.5; 3.3.1, p.4
Particle count, automatic (per size range)	—	5–15 µm: 10,000 max; 16–25: 1,000; 26–50: 150; 51–100: 20; >100: 5	Table II, p.6
High-temperature stability	200 °C, 100 h	Viscosity change at 40 °C ≤ 5 %; acid number rise ≤ 0.25 mg KOH/g; no precipitate	3.3.5, p.4; 4.4.3, p.7
Corrosion and oxidation stability (ASTM D4636)	121 °C, 168 h	Acid number change ≤ 0.5; viscosity change at 40 °C ≤ 5 %; no gumming	Table I, p.5
Operating range	—	−54 °C to +200 °C	1.1 Scope, p.2
Storage range	—	−54 °C to +50 °C	6.1.1, p.8

Limits are from MIL-PRF-87252D (23 November 2015). The specification has no density, specific heat, thermal conductivity or expansion requirement.

Typical Values in MIL-PRF-87252D Table III (informational, not requirements)

Characteristic	Inherent value	In SI units	Compare ROYCO 602 fit
Specific gravity at 25 °C (77 °F)	0.789	789 kg/m³ (SG × 1000)	789 kg/m³
Specific gravity at 15.6 °C (60 °F)	0.800	800 kg/m³ (SG × 1000)	796 kg/m³
Coefficient of thermal expansion (cm³/cm³·°C)	8.1×10⁻⁴	8.1×10⁻⁴ 1/K (temperature not stated)	8.3×10^-4 at 20 °C
Thermal conductivity at −40 °C (−40 °F)	4.5×10⁻⁴ cal·cm/(s·cm²·°C)	0.188 W/(m·K)	0.149 (extrapolated)
Thermal conductivity at 0 °C (32 °F)	3.8×10⁻⁴	0.159 W/(m·K)	0.145
Thermal conductivity at 150 °C (302 °F)	3.0×10⁻⁴	0.126 W/(m·K)	0.130
Specific heat at −40 °C (−40 °F)	0.48 cal/(g·°C)	2008 J/(kg·K)	1982 (extrapolated)
Specific heat at 25 °C (77 °F)	0.53	2218 J/(kg·K)	2206
Specific heat at 75 °C (167 °F)	0.55	2301 J/(kg·K)	2378
Specific heat at 149 °C (300 °F)	0.65	2720 J/(kg·K)	2633

Table III, printed p.8. The thermal conductivity in Table III is higher than the ROYCO 602 sheet trend at low temperature (see the thermal conductivity page). The two are not averaged. Specific heat agrees within about 3 %.

MIL-PRF-87252 vs 60/40 Ethylene Glycol–Water — Thermophysical Properties

Property	Temperature	MIL-PRF-87252 (ROYCO 602 typical)	60/40 EG-water (CoolProp)	PAO / EG-water
Density (kg/m³)	-40 °C (-40 °F)	831.6*	1102.1	0.75
	20 °C (68 °F)	792.7	1077.1	0.74
	100 °C (212 °F)	739.2	1020.8	0.72
Specific heat (kJ/(kg·K))	-40 °C (-40 °F)	1.982*	2.684	0.74
	20 °C (68 °F)	2.189	3.098	0.71
	100 °C (212 °F)	2.464	3.476	0.71
Thermal conductivity (W/(m·K))	-40 °C (-40 °F)	0.1486*	0.3293	0.45
	20 °C (68 °F)	0.1426	0.3567	0.40
	100 °C (212 °F)	0.1347	0.3933	0.34
Kinematic viscosity (mm²/s)	-40 °C (-40 °F)	277.00*	140.83	1.97
	20 °C (68 °F)	9.23	4.50	2.05
	100 °C (212 °F)	1.72	0.81	2.12
Dynamic viscosity (mPa·s)	-40 °C (-40 °F)	230.363*	155.209	1.48
	20 °C (68 °F)	7.320	4.845	1.51
	100 °C (212 °F)	1.271	0.829	1.53
Prandtl number	-40 °C (-40 °F)	3072.3*	1265.3	2.43
	20 °C (68 °F)	112.3	42.1	2.67
	100 °C (212 °F)	23.3	7.3	3.18
Thermal diffusivity (×10⁻⁸ m²/s)	-40 °C (-40 °F)	9.02*	11.13	0.81
	20 °C (68 °F)	8.22	10.69	0.77
	100 °C (212 °F)	7.39	11.08	0.67
β (×10⁻⁴ 1/K)	-40 °C (-40 °F)	7.70*	1.93	3.99
	20 °C (68 °F)	8.29	5.43	1.53
	100 °C (212 °F)	9.20	7.47	1.23

“*” marks extrapolated PAO values (see the property pages). The glycol mixture is 60 % ethylene glycol by mass, CoolProp 7.2.0 INCOMP::MEG[0.6], from the Melinder (2010) correlations, valid −50 to 100 °C. It freezes near −51 °C (CoolProp value). Glycol–water values at −40 °C are near the edge of the fitted range.

Flash, Fire, Pour Point and Electrical — Manufacturer Typical Values

Property	ROYCO 602 (2004)	ROYCO 602 (LANXESS 2020)	AeroShell Fluid 602 (2003)	RADCOLUBE 500M (E)	MIL-PRF-87252D limit
Flash point (ASTM D92)	158 °C	158 °C	160 °C	172 °C	150 °C min
Fire point (ASTM D92)	175 °C	173 °C	171 °C	178 °C	160 °C min
Pour point (ASTM D97)	−100 °F (−73 °C)	printed −100 °C (a misprint; the 2004 sheet says −100 °F)	−73 °C	—	no limit
Viscosity index (ASTM D2270)	145	145	145	—	no limit
Acid number (mg KOH/g)	< 0.01	0.03	< 0.01	0.01	0.20 max
Water (ppm)	< 30	20	35	26	50 max
Dielectric breakdown voltage (kV)	50	53	47	40	35 min
Dielectric constant at 400 Hz	2.10	2.10	2.10	—	no limit
Volume resistivity (ohm-cm)	2.9×10¹⁵	24.3×10¹⁰ (as printed)	2.9×10¹⁵ (at 25 °C)	2.1×10¹³	1.0×10¹⁰ min
Evaporation loss	17 % (400 °F, 6.5 h)	—	17 %m (204 °C, 6.5 h)	—	no limit

All sheet values are single-lot typical values with no stated uncertainty. The pour point is well below the −54 °C low end of the operating range. ROYCO 602 and AeroShell Fluid 602 sheets give the same density, specific heat and conductivity tables.

Manufacturer Typical Values (not measurements)

Source	Property	Typical value
ROYCO 602 (ANDEROL 2004)	Density, dilatometer (g/cm³)	0.8058 @ 0 °C; 0.7392 @ 100 °C; 0.6768 @ 190 °C
ROYCO 602 (ANDEROL 2004)	Specific gravity, API gravity	0.7999 @ 15.6 °C (ASTM D1298); API 45.3
ROYCO 602 (ANDEROL 2004)	Specific heat (ASTM D2766, cal/(g·°C))	0.49 @ −17.8 °C; 0.54 @ 37.8 °C; 0.63 @ 149 °C; 0.72 @ 260 °C
ROYCO 602 (ANDEROL 2004)	Thermal conductivity (cal/(hr·cm·°C))	1.26 @ −17.8 °C; 1.21 @ 37.8 °C; 1.12 @ 149 °C; 1.02 @ 260 °C
ROYCO 602 (ANDEROL 2004)	Expansion coefficient, dilatometer (1/°C)	0.00083 (0–50 °C); 0.00092 (50–100); 0.00103 (100–150); 0.00117 (150–190)
ROYCO 602 (ANDEROL 2004)	Kinematic viscosity (ASTM D445, mm²/s)	1087 @ −54 °C; 277 @ −40 °C; 5.19 @ 40 °C; 1.72 @ 100 °C
AeroShell Fluid 602 (2003)	Kinematic viscosity (mm²/s)	1094 @ −54 °C; 280 @ −40 °C; 5.29 @ 40 °C; 1.77 @ 100 °C
AeroShell Fluid 602 (2003)	Thermal conductivity method	Heat probe method (as printed)
ROYCO 602 (LANXESS 2020)	Kinematic viscosity (mm²/s)	1137 @ −54 °C (ASTM D2532); 274 @ −40 °C; 5.18 @ 40 °C; 1.72 @ 100 °C
ROYCO 602 (LANXESS 2020)	Density	6.66 lb/gal (temperature not stated); API 45.4
RADCOLUBE 500M (MIL-PRF-87252E)	Kinematic viscosity (mm²/s)	1078 @ −54 °C (1.5 h); 1100 (3.0 h); 261 @ −40 °C; 5.0 @ 40 °C; 1.68 @ 100 °C

Single-lot typical values from data sheets of products sold against the specification. They are not measurements made for this site and carry no stated uncertainty.

Sources

US Department of Defense, MIL-PRF-87252D, Performance Specification: Coolant Fluid, Hydrolytically Stable, Dielectric, 23 November 2015. everyspec.com. Tables I, II, III, scope and storage ranges. Opened and read 25 Oct 2026.
ANDEROL Inc., ROYCO 602 Coolant for Aircraft Avionics Systems data sheet (edited 19 Oct 2004). Royco602.pdf. Manufacturer typical values: density, specific heat, thermal conductivity, expansion, viscosity, flash, fire, electrical values.. Opened and read 25 Oct 2026.
Shell Aviation, AeroShell Fluid 602, The AeroShell Book, Edition 18 (2003), pp. 240–243. AeroShellfluid602.pdf. same tables, plus MIL-PRF-87252C limits and typical viscosity. Opened and read 25 Oct 2026.
LANXESS, ROYCO 602 Aviation Performance Fluid Product Data Sheet, edition 2020-10-26. LANXESS_ROYCO_602_EMEA_EN.pdf. 2020 sheet; qualification claim; typical viscosity and electrical values. Opened and read 25 Oct 2026.
Radco Industries, RADCOLUBE 500M Coolant Fluid, Hydrolytically Stable, Dielectric (MIL-PRF-87252E data sheet). RADCO-500M-AIR-TDS.pdf. MIL-PRF-87252E qualified product; typical results. Opened and read 25 Oct 2026.
CoolProp 7.2.0, incompressible fluid INCOMP::MEG[0.6] (60 % ethylene glycol in water by mass), 1 atm. coolprop.org/fluid_properties/Incompressibles.html. The CoolProp page cites Å. Melinder, Properties of Secondary Working Fluids for Indirect Systems, IIF-IIR Publishing, 2010, as the source of the MEG data (T_min −100 °C, T_max 100 °C, mass fraction 0 to 0.60). The Melinder book itself was not opened. Comparison fluid.

Castrol Brayco Micronic 889 is mentioned only as a known product; its data sheet could not be opened. No government or journal source with measured thermophysical data was found. Typical values carry no stated uncertainty.

MIL-PRF-87252 General Properties

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