What does it mean when an oil meets MIL-H-5606 specifications?
There are different oils and lubricants for just about any application, and certain machines hold higher standards for lubricants than others.
The US Military developed the MIL-H-5606 oil specification to set performance levels for hydraulic fluids they use in aircraft. This specification was created so that any brand of oil can be created to perform at that designated level.
MIL stands for Military, H for hydraulic fluid, and 5606 designates oil's the performance properties.
The specifications for this oil are as follows: it has an iso viscosity level of 15 and is thin compared to most oils so it can flow at a colder temperature. This is needed for planes flying in the sky, where it's cooler.
Synthetic or Mineral-Based?
You may be thinking that this must be a synthetic oil, but it's not. This is a highly-refined mineral-based oil derived from crude.
As a mineral-based oil, it is highly refined to remove impurities and increase performance levels. This oil is very "clean." It contains minimal if any paraffin (wax) that would affect flow rate and performance at low temperatures. As a result, this oil performs at temperatures as cool as -60 F.
It is also packaged in a way that eliminates chances for moisture and condensation buildup, which is necessary otherwise the oil if it contains moisture can freeze at high altitudes.
Is this the oil for you?
A lot of equipment manufacturers call for this lubricant as well because it performs so well in cold temperatures.
MIL-PRF-5606-H is the current specification the US Military uses for a grade of hydraulic oil to be used in military aircraft. Hydraulic oil manufacturers pay for the military to inspect and give that grade to their oil, so the cost of it is higher.
The Aircraft Hydraulic Systems MIL-PRF-5606H are considered "super clean." Most hydraulic applications calling for an oil meeting MIL-H-5606 are land-based hydraulic applications that don't need to meet the "super clean" requirement.
If you're looking for a land-based 5606 lubricant, there are less costly alternatives, such as Kendall's Hyken Glacial Blu and Mobil's Aero HFA. They meet all the requirements of MIL-H-5606, but the cost is lower because the manufacturer doesn't pay the approval fees for the MIL-PRF-5606 H approval.
Click here for PSC's full line of MIL-H-5606 lubricants.