MIL-PRF-5606 Thermal Conductivity Chart

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Measured values for MIL-PRF-5606 (NADC-79248-60 Table 8) at -18, 38, 93, 149 and 204 °C, shown as markers.
The line is a straight-line fit drawn only from -18 to 204 °C; nothing is extrapolated.

The blue MIL-PRF-23699 series covers its measured range, 28.4 to 226.3 °C (83 °F to 439 °F), and is not extended beyond it.

Data from: NADC-79248-60 (Conte & Hammond, 1980), DTIC ADA081597, Table 8 (measured); MIL-PRF-23699 data from NIST IR 8263, Table A4.

Toggle data sets by clicking the legend.

MIL-PRF-5606 Thermal Conductivity Calculator
Degrees (°F):
Degrees (°C):
W / (m·K):  
mW / (m·K):  
BTU / (h·ft·°F):  
BTU·in / (h·ft²·°F):  
W / (cm·K):  
MIL-PRF-23699 (W / (m·K)):  

Calculator valid -0.4 °F to 399.2 °F (-18 °C to 204 °C), using the linear fit to the NADC-79248-60 Table 8 measurements. The MIL-PRF-23699 row is shown only within that fluid's 83.1–439.3 °F (28.4–226.3 °C) measured range; elsewhere it shows —.

Thermal Conductivity of MIL-PRF-5606 Petroleum Hydraulic Fluid
About This Data

The thermal conductivity values are the Table 8 entries of NADC-79248-60 (Conte & Hammond, Naval Air Development Center, 1980, DTIC ADA081597), tabulated in W/(m·K) at -18, 38, 93, 149 and 204 °C (-0.4, 100.4, 199.4, 300.2 and 399.2 °F). The report does not state the measurement method, the specification revision (MIL-H-5606 predates the MIL-PRF designation) or the lot tested, and it gives no uncertainty.

The straight line k = 0.13822 − 0.000077493 · T°C W/(m·K) is the least-squares fit to the five measured points. It departs from the tabulated values by at most 0.0007 W/(m·K), at 149 °C, and is used only between -18 °C and 204 °C. The chart and calculator are not extended beyond those temperatures.

MIL-PRF-5606 is a petroleum-based (mineral oil) aircraft hydraulic fluid, dyed red. Across its range the fitted thermal conductivity falls by about 0.017 W/(m·K), from 0.1396 W/(m·K) at -18 °C to 0.1224 W/(m·K) at 204 °C.

MIL-PRF-5606 — Thermal Conductivity vs. Temperature
Temp (°C) Temp (°F) λ measured (W/m·K) λ measured (mW/m·K) Linear fit (W/m·K)
-18-0.40.1401400.13961
38100.40.1351350.13528
93199.40.1311310.13101
149300.20.1261260.12667
204399.20.1231230.12241

Columns 3–4 are the NADC-79248-60 Table 8 measurements. Last column: straight-line fit, valid -18–204 °C. Method, specification revision and lot are not stated in the report, and no uncertainty is given.

MIL-PRF-5606 vs MIL-PRF-23699

MIL-PRF-5606 is a petroleum (mineral oil) hydraulic fluid; MIL-PRF-23699 is a polyol-ester turbine engine oil. Over the temperatures where both have data (28.4 to 204 °C), MIL-PRF-5606 conducts heat about 6 % less well at the cold end and about 4 % better at the hot end. The two curves cross near 151 °C.

Temp (°C) Temp (°F) MIL-PRF-5606 (W/m·K) MIL-PRF-23699 (W/m·K) Difference (W/m·K) Difference (% of 23699)
-18-0.40.13961———
032.00.13822———
28.483.10.136020.14510-0.00908-6.3 %
38100.40.135280.14373-0.00845-5.9 %
60140.00.133570.14059-0.00702-5.0 %
93199.40.131010.13589-0.00488-3.6 %
126.8260.20.128390.13070-0.00231-1.8 %
149300.20.126670.12688-0.00021-0.2 %
159.9319.80.125830.125000.000830.7 %
192.7378.90.123290.119300.003993.3 %
204399.20.122410.117480.004934.2 %
226.3439.3—0.11390——

MIL-PRF-5606 values use the linear fit to the NADC-79248-60 Table 8 measurements, -18–204 °C only; at the five measured temperatures the fit differs from the measured value by at most 0.0007 W/(m·K). MIL-PRF-23699 values are linearly interpolated between the NIST IR 8263 Table A4 points, 28.4–226.3 °C only. "—" means the fluid has no data at that temperature; extrapolated values are deliberately not used. Differences are computed from the values shown. The two datasets come from different sources and labs, so small differences should not be over-interpreted.

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. Table 8 (thermal conductivity), 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. Identification of the fluid.
  • Bruno et al., Thermophysical Properties of Polyol Ester Lubricants, NIST IR 8263, 2019. doi.org/10.6028/NIST.IR.8263. MIL-PRF-23699 comparison data (Table A4).

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

Cite This Work