Originally Posted By: ekpolk
FWIW, and I may be wrong on this since it's been so long, but as I recall from my flying days, we almost always used MIL-L-23699 oil for our jet engines, but there was an alt spec I don't remember for when the temps went below either -40 or -60C. I don't know what this stuff was, but it must have been pretty special to stay pumpable that cold, and protect a superhot jet engine while running. Obviously, SOME oil can do this.
The lower temperature jet engine oil is MIL-PRF-7808, which is designed to start at -60F as opposed to the -40 capability of the 23699 oil. Virtually all of the 7808 oil used by the military came from Hatco, as did most of the 23699. The 23699 has a viscosity of 5 cSt @ 100C and a typical pour point of -70F, while the 7808 has a viscosity of 3 cSt @ 100C and a pour point typically below -80F. Both are lighter than a 0W-10 and based entirely on POEs.
The 7808 oil is used mainly by the US Air Force since they operate bases in Arctic regions. This is changing, however, because a recent Air Force study found that the temperatures at these bases really don't go below about -40, and the fuel won't pump below -40 either. The Air Force is now working on a new specification for a single 5 cSt oil suitable for all of the armed forces.
Tom NJ
FWIW, and I may be wrong on this since it's been so long, but as I recall from my flying days, we almost always used MIL-L-23699 oil for our jet engines, but there was an alt spec I don't remember for when the temps went below either -40 or -60C. I don't know what this stuff was, but it must have been pretty special to stay pumpable that cold, and protect a superhot jet engine while running. Obviously, SOME oil can do this.
The lower temperature jet engine oil is MIL-PRF-7808, which is designed to start at -60F as opposed to the -40 capability of the 23699 oil. Virtually all of the 7808 oil used by the military came from Hatco, as did most of the 23699. The 23699 has a viscosity of 5 cSt @ 100C and a typical pour point of -70F, while the 7808 has a viscosity of 3 cSt @ 100C and a pour point typically below -80F. Both are lighter than a 0W-10 and based entirely on POEs.
The 7808 oil is used mainly by the US Air Force since they operate bases in Arctic regions. This is changing, however, because a recent Air Force study found that the temperatures at these bases really don't go below about -40, and the fuel won't pump below -40 either. The Air Force is now working on a new specification for a single 5 cSt oil suitable for all of the armed forces.
Tom NJ