MIL-PRF-87252 Viscosity: PAO Coolant Chart

MIL-PRF-87252 Kinematic Viscosity Chart

MIL-PRF-87252 PAO coolant kinematic viscosity versus temperature chart in mm2/s with specification limits and 60/40 ethylene glycol and water

About the data: no government report or journal paper with measured MIL-PRF-87252 properties was found. The curve is drawn through the ROYCO 602 data sheet points (manufacturer typical values, identical in the AeroShell Fluid 602 listing). Three other product sheets and the MIL-PRF-87252D limits are shown as markers. No uncertainty is stated.

Sheet points: −54, −40, 40 and 100 °C (−65.2, −40, 104 and 212 °F). The Y axis is logarithmic. The curve is a piecewise ASTM D341 interpolation. There is no measurement between −40 °C and 40 °C, so the dotted span is interpolation only. The dashed line above 100 °C is extrapolated.

Circles: ROYCO 602 (2004). Squares: AeroShell Fluid 602. Hollow triangles: ROYCO 602 (LANXESS 2020). Hollow diamonds: RADCOLUBE 500M. Black crosses are the MIL-PRF-87252D Table I limits (maximum at −54 and −40 °C, minimum at 40 and 100 °C), not measurements. The blue line is 60/40 ethylene glycol–water (ν = μ/ρ, CoolProp), drawn from −50 to 100 °C only.

Data from: ROYCO 602 (ANDEROL, 2004), AeroShell Fluid 602, ROYCO 602 (LANXESS, 2020), RADCOLUBE 500M; MIL-PRF-87252D Table I; comparison from CoolProp 7.2.0 (Melinder 2010).

Toggle data sets by clicking the legend.

MIL-PRF-87252 Dynamic (Absolute) Viscosity Chart

MIL-PRF-87252 PAO coolant dynamic viscosity versus temperature chart in mPa-s compared with 60/40 ethylene glycol and water

Computed from kinematic viscosity × density (μ = ν·ρ). The Y axis is logarithmic. The density fit is measured from 0 °C, and the viscosity data end at 100 °C, so the solid line is valid only from 0 to 100 °C (32 to 212 °F). The dashed parts are extrapolated.

Circles are ν times the fitted density at the four sheet temperatures. The blue line is 60/40 ethylene glycol–water from CoolProp (−50 to 100 °C only).

Toggle data sets by clicking the legend.

MIL-PRF-87252 Viscosity Calculator

Degrees (°F):

Degrees (°C):

Kinematic Viscosity

mm²/s (= cSt):

Centistokes (cSt):

Stokes (cm²/s):

m²/s:

in²/s:

ft²/s:

Dynamic (Absolute) Viscosity

mPa·s (= cP):

Centipoise (cP):

Poise (g/(cm·s)):

Pa·s (Poiseuille):

lbm/(ft·s):

kg/(m·h):

Data basis and comparison

Kinematic basis:

Dynamic basis:

60/40 EG-water, kinematic (cSt):

60/40 EG-water, dynamic (mPa·s):

Valid −54 °C to 150 °C (−65.2 °F to 302 °F), atmospheric pressure. Kinematic viscosity is interpolated between the ROYCO 602 points (no measurement between −40 and 40 °C) and extrapolated above 100 °C. Dynamic viscosity is measured-range only from 0 to 100 °C. The “Data basis” rows say which applies. The glycol rows are shown only from −50 to 100 °C.

Viscosity of MIL-PRF-87252 PAO Coolant

About This Data

MIL-PRF-87252D limits the kinematic viscosity to 1300 mm²/s at −54 °C and 300 at −40 °C (maximums), with minimums of 5.0 at 40 °C and 1.65 at 100 °C (Table I, p.5). The fluid is a low-viscosity PAO, about 5 mm²/s at 40 °C with a viscosity index near 145, so it stays pumpable at −54 °C.

Four product data sheets give typical values at those same four temperatures: ROYCO 602 (ANDEROL 2004 and LANXESS 2020), AeroShell Fluid 602 and RADCOLUBE 500M (qualified to MIL-PRF-87252E). They are single-lot typical values with no uncertainty. The curve follows the 2004 ROYCO 602 sheet because it is the same sheet that gives density, specific heat and conductivity.

The curve is a piecewise ASTM D341 interpolation: between neighbouring sheet points it is a straight line in Y = log₁₀(log₁₀(ν + 0.7)) against X = log₁₀(T_°C + 273.15), with ν in cSt. It passes exactly through the four points. A single D341 line through all four misfits by up to 9 %, so it is not used. Between −40 and 40 °C there is no measurement, so values there are interpolation only. Above 100 °C the last segment is extended and marked as extrapolated.

Dynamic viscosity is ν times density. The density fit starts at 0 °C, so dynamic viscosity below 0 °C is flagged as extrapolated. See density, the Prandtl number, and pipe velocity and orifice flow for line sizing. For glycol–water see ethylene glycol viscosity.

MIL-PRF-87252 Kinematic Viscosity: Limits and Product Data Sheets

Temp (°C)	Temp (°F)	MIL-PRF-87252D limit (mm²/s)	ROYCO 602 (ANDEROL 2004) (mm²/s)	AeroShell Fluid 602 (2003) (mm²/s)	ROYCO 602 (LANXESS 2020) (mm²/s)	RADCOLUBE 500M (MIL-PRF-87252E) (mm²/s)
-54	-65.2	≤ 1300 (max)	1087	1094	1137	1078
-40	-40.0	≤ 300 (max)	277	280	274	261
40	104.0	≥ 5.0 (min)	5.19	5.29	5.18	5.0
100	212.0	≥ 1.65 (min)	1.72	1.77	1.72	1.68

Specification limits are Table I of MIL-PRF-87252D (printed p.5): maximums at −54 and −40 °C, minimums at 40 and 100 °C. The −54 °C reading is taken at 1.5 hours and must also stay at or below 1300 at 3 hours and 72 hours. Sheet values are manufacturer typical values for single lots of four products. The Radco sheet reports a 3.0 hour reading of 1100 at −54 °C. The lots differ by up to 5 % at −54 °C and 7 % at −40 °C.

MIL-PRF-87252 Viscosity vs. Temperature

Temp (°C)	Temp (°F)	ν (mm²/s)	μ (mPa·s)	ρ used (kg/m³)	Basis of ν
-54	-65.2	1087.0	913.697*	840.6*	Sheet point
-40	-40.0	277.0	230.363*	831.6*	Sheet point
-20	-4.0	58.268	47.708*	818.8*	Interpolated; no measurement between −40 and 40 °C
0	32.0	19.945	16.072	805.8	Interpolated; no measurement between −40 and 40 °C
20	68.0	9.234	7.320	792.7	Interpolated; no measurement between −40 and 40 °C
40	104.0	5.190	4.046	779.5	Sheet point
60	140.0	3.301	2.529	766.2	Interpolated between sheet points
80	176.0	2.304	1.734	752.8	Interpolated between sheet points
100	212.0	1.720	1.271	739.2	Sheet point
120	248.0	1.351*	0.980*	725.5	Extrapolated above 100 °C
150	302.0	1.010*	0.712*	704.8	Extrapolated above 100 °C

Curve: piecewise ASTM D341 through the ROYCO 602 points. “*” marks values that rest on extrapolation: ν above 100 °C, or μ and ρ outside 0–100 °C (the density fit is measured from 0 °C, the viscosity data end at 100 °C). μ = ν·ρ/1000.

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

The PAO coolant stays thin in the cold. At −40 °C it is about 277 mm²/s, against about 141 mm²/s for 60/40 glycol–water. Above about 20 °C the glycol mixture is the thinner fluid. This is why PAO is used in unheated avionics bays and radar pods at high altitude.

Temp (°C)	Temp (°F)	PAO ν (mm²/s)	MEG-60 ν (mm²/s)	MEG-60 / PAO (ν)	PAO μ (mPa·s)	MEG-60 μ (mPa·s)	MEG-60 / PAO (μ)
-50	-58.0	706.9	361.7	0.51	592.43*	399.21	0.67
-40	-40.0	277.0	140.8	0.51	230.36*	155.21	0.67
-20	-4.0	58.27	30.60	0.53	47.71*	33.54	0.70
0	32.0	19.95	9.99	0.50	16.07	10.87	0.68
20	68.0	9.23	4.50	0.49	7.32	4.84	0.66
40	104.0	5.19	2.56	0.49	4.05	2.73	0.67
60	140.0	3.30	1.69	0.51	2.53	1.78	0.70
80	176.0	2.30	1.19	0.51	1.73	1.23	0.71
100	212.0	1.72	0.81	0.47	1.27	0.83	0.65

“*” marks PAO μ that uses an extrapolated density (below 0 °C). MEG-60 values are CoolProp 7.2.0 (Melinder 2010), valid here from −50 to 100 °C only.

Sources

ANDEROL Inc., ROYCO 602 Coolant for Aircraft Avionics Systems data sheet (edited 19 Oct 2004). Royco602.pdf. Manufacturer typical values: kinematic viscosity at −54, −40, 40 and 100 °C; viscosity index 145.. Opened and read 25 Oct 2026.
Shell Aviation, AeroShell Fluid 602, The AeroShell Book, Edition 18 (2003), pp. 240–243. AeroShellfluid602.pdf. typical viscosities, plus the MIL-PRF-87252C limits. 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. typical viscosities (−54 °C by ASTM D2532). 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. typical results and the MIL-PRF-87252E requirement column; qualification AFPET/PTPS 19-014. Opened and read 25 Oct 2026.
US Department of Defense, MIL-PRF-87252D, Performance Specification: Coolant Fluid, Hydrolytically Stable, Dielectric, 23 November 2015. everyspec.com. Table I (p.5) viscosity limits; 3.3.3 (p.4) low-temperature stability. 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. Viscosity and density of the comparison fluid.

No measured viscosity series from a government report or journal paper was found. The sheets are single-lot typical values.

MIL-PRF-87252 Viscosity: PAO Coolant

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