HI temp Mil-H-83232 hydraulic fluid

[scsmith]

After reading some old threads on the subject, I am going to switch over to the higher-temperature hydraulic fluid, Mil-H-83232 (Royco 782).

I am replacing the O-rings in the brake calipers with Viton O-rings, Mil-R-83248-218.

Is there any reason to be concerned that the new hydraulic fluid might not be compatible with the rubber parts in my master cylinders? It is supposedly compatible with Mil-H-5606, even mixable. So I'm not planning to do anything other than drain the system and re-fill.

[BlndRvtr]

Curious, why the changeover?

George

[FORANE]

I switched to 782 from 5606 in both brakes and gear. Brakes were simply drained and refilled; gear was mixed. Have experienced no issues whatsoever after years of use.

[rocketbob]

Mobil 1 synthetic ATF that you can get at Walmart or any parts store has a higher flash point than Royco 782.

[RV6_flyer]

Originally Posted by scsmith

After reading some old threads on the subject, I am going to switch over to the higher-temperature hydraulic fluid, Mil-H-83232 (Royco 782).

I am replacing the O-rings in the brake calipers with Viton O-rings, Mil-R-83248-218.

Is there any reason to be concerned that the new hydraulic fluid might not be compatible with the rubber parts in my master cylinders? It is supposedly compatible with Mil-H-5606, even mixable. So I'm not planning to do anything other than drain the system and re-fill.

Been using it for about 10-years. I have had no issues when I did the same thing you are doing. Have used my MIL-H-83232 on several other airplanes and they were done the same way.

[scsmith]

Originally Posted by BlndRvtr

Curious, why the changeover?

George

The primary reason is higher flash point, and self-extinguishing properties. I tend to brake firmly - I try to make every landing stopped in under 1000 ft.

Every now and then you hear of a brake fire.

[KatanaPilot]

If you have Matco components, reach out to George Happ (also an Aero type) - owner of Matco. tech@matcomfg.com

I asked him that question back in 2017 and he answered "Royco 782 is a version of Mil-H-83282 which is a high flashpoint aircraft hydraulic fluid that is compatible with the Buna nitrile seals we use."

Van's says the same thing on their web store - "Royco 782 is a synthetic fire resistant hydraulic fluid compatible with the seals in the kit brake components."

[fl-mike]

Originally Posted by rocketbob

Mobil 1 synthetic ATF that you can get at Walmart or any parts store has a higher flash point than Royco 782.

^^^^ +1

12 years so far with standard components. No issues.

(as a side note, I was thinking the built-in fire extinguishing thread should focus the nozzles on the brakes rather than the engine!)

[John-G]

Originally Posted by rocketbob

Mobil 1 synthetic ATF that you can get at Walmart or any parts store has a higher flash point than Royco 782.

I too went with a synthetic ATF fluid ... except I chose Amsoil multi-vehicle synthetic ATF because it has a slightly higher flash point of 453?. Have been using it for three years ... without any issues so far.

One nice thing is if I have any issues when away from home that requires adding fluid, Mobil 1 synthetic ATF can be added without causing any compatibility issues .... and it is available most everywhere.

Happy flying,

[FORANE]

Originally Posted by rocketbob

Mobil 1 synthetic ATF that you can get at Walmart or any parts store has a higher flash point than Royco 782.

Looking up flash points for the two,
Mobil one: 420f
Royco: 450f

Close but doesn't appear to be greater.