REFLECTOR: RG System hydraulic oil

[Al Gietzen]

Jeff;

When I first filled my gear hydraulics, I used ATF fluid because that is
what the pump is designed for.  It worked very well.  The principal
difference for our application between it and the mil spec (is it 5606?) is
the change of viscosity with temperature.  The mil spec stuff has lower
viscosity and it stays low all the way to minus numbers like -50 F; which
planes that fly very high encounter routinely.

Later, after some discussion on this forum, I became concerned about the
viscosity of ATF at very low temperatures - like -20F  (thinking that some
day I may be flying in North Dakota in the winter time, silly me).  After
checking out the data, I concluded that at very low temps the higher
viscosity could prevent free-fall of the gear in the event of
electric/hydraulic failure.  I then decided to change the fluid.

I had at least one opinion that the fluids should definitely not be mixed -
that it would result in seal failure.  Not wanting to chance it, I worked
out a procedure for changing the fluid (which I will share if any one is
interested).  The first thing I noticed with the mil spec fluid is a MUCH
noisier pump.  I suspect it is also more likely to leak as the seals age,
although mine has now been in for about 8 years and is still working fine.

I hind sight, if I were doing it over, I'd probably leave the ATF in there.
Definitely the pump likes it better, and I don't think I'm going to want to
fly this airplane at temps of -20F.

FWIW,

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Jeffrey Clough
Sent: Wednesday, August 16, 2006 10:37 PM
To: reflector at awpi.com
Subject: REFLECTOR: RG System hydraulic oil

I used a local hydraulic shop for some help rebuilding my main gear 
hydraulic cylinder after I dinged up one of the seals and caused it to 
leak. (Caused by a drop of epoxy on the shaft)  I asked them if I could 
purchase some add'l  hydraulic oil and if what they had matched my mil 
spec oil....they said,  'Just use ATF' (Automatic Transmission 
Fluid).......they even said they could be mixed with no 
consequences....has anybody heard of this ...or tried it?
Jeff Clough   173RG Franklin IVO Clamshell
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