That's the info that was missing from your first post - the Parker pump manual actually specifies ATF, which you say has about twice the viscosity of 5606. I would guess that the internal pump leakage makes reaching the rated pressure problematic with 5606. I would use ATF - it'll be compatible with all the other seals in the hydraulic system. On the other hand, 5606 will probably work okay - the pump is only used intermittently, so it won't get hot enough for the difference in viscosity to mean anything. I also suspect that the reason for the ATF spec is that the same pump is used for lots of other things, like the tilt system in boat stern-drives and hydraulic lifts for pickup snowplows. And here you thought it was a fine FAA-approved genuine aircraft part :-)
Gary Casey
The Parker manual doesn't specify 5606, that's why I ask. The manual specif=
ies "ATF, OD18, or other clean hydraulic oil with a viscosity of 150-300 SU=
S at 38C", if another type is used "consult the factory"
The label on Phillips 5606 states that it is not to be used on natural rubb=
er. And the MIL-SPEC viscosity is outside of the Parker manual's recommenda=
tion.
Two votes for 5606 from the List so far. Anyone have experience with anoth=
er fluid?
Joe
Czabaranek