HyJet Viscosity: Phosphate Ester Calculator & Chart

HyJet Kinematic Viscosity Chart

HyJet IV-A plus and HyJet V kinematic viscosity vs temperature in degrees F, compared with Skydrol 500B-4, LD-4, PE-5 and Skydrol 5

Data range: −65 °F to 261.7 °F (−53.9 °C to 127.6 °C). Circles and diamonds are the five typical values printed on the ExxonMobil data sheets (ASTM D445).

The lines between the printed points are interpolated on the ASTM D341 double-log scale. The y-axis is logarithmic. Nothing is extrapolated.

The last printed point is labelled "127.6 °C (260 °F)" on the data sheets. These two do not match (260 °F is 126.7 °C). The chart uses the °C value as printed.

Skydrol grades are shown dashed for comparison, copied unchanged from the Skydrol Viscosity page (Eastman EASAF7870). Toggle data sets by clicking the legend.

HyJet Viscosity Calculator

Grade:

Degrees (°F):

Degrees (°C):

Kinematic Viscosity

mm²/s (= cSt):

Centistokes (cSt):

Stokes (cm²/s):

m²/s:

in²/s:

ft²/s:

Dynamic (Absolute) Viscosity, 15.6–100 °C only

mPa·s (= cP):

Centipoise (cP):

Poise (g/(cm·s)):

Pa·s (Poiseuille):

lbm/(ft·s):

kg/(m·h):

ρ used (kg/m³):

Kinematic viscosity is valid −65 °F to 261.7 °F (−53.9 °C to 127.6 °C). "Out of Range" outside it. Dynamic viscosity is shown only from 15.6 to 100 °C, where a derived density exists (see HyJet Density).

Kinematic Viscosity of HyJet Phosphate Ester Hydraulic Fluid

About This Data

ExxonMobil prints kinematic viscosity (ASTM D445) at five temperatures for HyJet IV-A plus and HyJet V. These are typical values, not measurements. The cold end is the main difference between the grades: 1320 cSt for IV-A plus and 1350 cSt for V at −53.9 °C (−65 °F). From −26.1 °C up the two grades print the same values within 2 cSt. Both have a viscosity index of 280 (ASTM D2270).

Between the printed points the page interpolates on the ASTM D341 double-log scale, the usual straight-line scale for viscosity against temperature. A single D341 line does not fit all five points. It is off by about 190 cSt at −53.9 °C. So each pair of neighbouring points is joined separately. The calculator returns "Out of Range" below −65 °F and above the last printed point.

Note on the hot point. The sheets print "127.6 °C (260 °F)". Those two temperatures differ by 1 °C. It may be a typing error, but we could not confirm which is right. This page uses 127.6 °C as printed. The difference changes the curve by less than 0.1 cSt.

The table also shows the limits printed on the ExxonMobil data sheet. These are the maker's limits column, which follows SAE AS1241. We have not read the standard itself. Both HyJet grades sit inside those limits at every printed temperature.

Skydrol is a different brand from a different maker (Eastman). At −53.9 °C both HyJet grades are thinner than Skydrol 500B-4 (2678 cSt) and Skydrol 5 (2085 cSt). They are thicker than Skydrol LD-4 (1164 cSt) and Skydrol PE-5 (1068 cSt). See Skydrol General Properties.

HyJet — Kinematic Viscosity vs. Temperature

Temp (°C)	Temp (°F)	HyJet IV-A plus (cSt)	HyJet V (cSt)	Limit printed on ExxonMobil sheet (cSt)	Skydrol 500B-4	Skydrol LD-4	Skydrol PE-5	Skydrol 5
−53.9	−65	1320	1350	2000 max	2678	1164	1068	2085
−26.1	−15	130	132	135 max	–	–	–	–
37.8	100	10.6	10.6	10.0–11.0	11.67	11.10	9.75	9.23
98.9	210	3.6	3.6	3.35–3.75	3.84	3.91	3.38	3.13
127.6 (printed)	260 (printed)	2.6	2.6	1.5 min	–	–	–	–

HyJet columns are the typical values printed on the ExxonMobil data sheets (ASTM D445). The limits column is as printed on the ExxonMobil data sheet. The Skydrol columns are Eastman typical values, copied unchanged from the Skydrol Viscosity page (only three temperatures are published). A dash means no value was printed.

HyJet — Dynamic Viscosity (derived)

Temp (°C)	Temp (°F)	ν (cSt), both grades	IV-A plus ρ (kg/m³)	IV-A plus μ (mPa·s)	V ρ (kg/m³)	V μ (mPa·s)
37.8	100	10.6	982.8	10.42	983.8	10.43
98.9	210	3.6	933.8	3.36	934.7	3.37

Derived: μ [mPa·s] = ν [cSt] × ρ [kg/m³] / 1000. The density is the derived straight line from HyJet Density, so it is not a measurement. It exists only at 15.6–100 °C. That leaves two printed viscosity temperatures, so the dynamic viscosity is given as a table and not as a chart.

Sources

Exxon Mobil Corporation, Exxon HyJet IV-A plus, Fire Resistant Phosphate Ester Aviation Hydraulic Fluid, product data sheet (3 pages, printed 31 Mar 2016). Reseller copy of the maker's PDF. Typical Properties table, pp.2–3. Accessed 29 Oct 2026. Re-checked against the Mobil web data sheet (2024 edition): same values.
Exxon Mobil Corporation, Exxon HyJet V, Fire Resistant Phosphate Ester Aviation Hydraulic Fluid, product data sheet (3 pages, printed 31 Mar 2016). Reseller copy of the maker's PDF. Typical Properties table, pp.2–3. Accessed 29 Oct 2026. Re-checked against the 2018 edition and the Mobil web data sheet (2024): same values.
Eastman Chemical Company, Skydrol aviation hydraulic fluids product comparison brochure, Publication EASAF7870. eastman.com. Skydrol comparison values, copied unchanged from the Skydrol Viscosity and Skydrol General Properties pages.
SAE International, AS1241, Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft. Cited by number only. Limits shown on this page are the limits printed on the ExxonMobil data sheets, not read from the standard.

All HyJet values are single typical values from the maker's data sheets ("values may vary within modest ranges"). Data are also listed in tools/hyjet-sources.json and tools/hyjet-derived.json. Related pages: HyJet Density, HyJet General Properties.

HyJet Kinematic Viscosity Calculator: Phosphate Ester Aviation Hydraulic Fluid

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