While cruising eBay for aircraft related items, I
came across this auction for Mil-H-83282
fluid in which the seller touted that it was a
"fire-resistant" alternative to our tried and
true 5606 hydraulic fluid used in our braking
systems. This piqued my interest so I
began researching the two products.
It's no secret that Mil 5606 has been around since
about the 1930's or 1940's. Mil-H-5606
is the standard red hydraulic fluid sold by Spruce,
Wicks, Chief, etc., typically to the GA
The military and commercial aviation have long ago
abandoned 5606 and moved to a
new fluid spec, Mil-H-83282. This spec was created
because the military was tired of
setting their airplanes on fire and wanted a
fire-resistant hydraulic fluid. By making this
request, one might construe that the military was
saying that 5606 was too "flammable"
for their applications and environments.
5606 is a petroleum base fluid with a very low flash
point (104C/219F). Now we know that
those temps are just barely above the boiling point
of water and we have an inkling that
our brake components probably have the potential to
get a lot hotter than that (think
about the rotor and pads).
HERE is an article on Cirrus brake overheating fires:
The Mil-H-83282 is also red, and compatible with
5606 fluid as well as seals created for
5606. However, it is a synthetic, with much higher
flash (237C/458F) and fire point (485F).
Additionally, when removed from the ignition
source, Mil-H-83282 is self-extinguishing.
The Cleveland piston seal for most of their calipers
is an ordinary MS28775-XXX nitrile o-
ring. Nitrile's temperature rating is - 65F to about
248F. A caliper seal with a 248F temp
limit is below automotive standards, (auto brake
systems are worked much harder in
actual use). Having a temperature excursion above
this 248F on your caliper seals can't
possibly be a good thing for the seal. Many of us
are familiar with the frequency of
having to replace nitrile rubber seals
on our calipers. Not exactly what I'd call acceptable
Gee, how often do we have to replace caliper seals
on our automobiles? Well, nuff said
about 1940's nitrile technology, especially
around flammable 5606 brake fluid!
Some folks in the Experimental community have
changed to Viton seals. I've installed
flurosilicone seals (-76F to +356F operating
range) in my last battle with nitrile rubber
seals on my Cleveland 30-66 calipers. With about
three years of service, I remain leak
Cleveland specifies that either Mil-H-5606 or
Mil-H-83282 fluid is acceptable and no
wonder, because the MIL. spec for Mil-H-83282
requires the following in it's compatibility
Miscible with fluids conforming to MIL-H-5606
and MIL-H-87257 from -40°C to 135°C.
When mixed with the test fluids, there shall be
no formation of resinous gums, sludge,
or insoluble materials.
A simple solution is to drain the system and install
Mil-H-83238 fluid with no need to
change seals. (except if you want better high temp
Viton or Flurosilicone seals. If you
have to top off the fluid in some out of the way
place with 5606 becuase it's all you could
find, it's completely compatible.
The MIL-PRF-83282 spec issued by the DoD can be