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  5606 Fluid Replacement Alternative

 

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

crowd.

 

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

free.

 

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

requirement:

Miscible with fluids conforming to MIL-H-5606 and MIL-H-87257 from -40C to 135C.

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 downloaded HERE

 

Aeroshell Fluid 41 (Mil-H-5606)

 

Aeroshell Fluid 31 (Mil-H-83282)

 

 

Royco 782 is a Mil-H-83282 spec fluid available from SkyGeek and Spruce for about

$12/quart and about $35/gallon

 

 

 

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