what causes oil to squeeze out of grease?

[Rick in PA]

I have a grease gun I use infrequently to lube the lawn equipment. I keep the grease gun in my oil change tool box and it always leaks oil. It seems the oil in the grease is squeezed out of the grease just sitting in the grease gun. I clean it up... and it reapeares, again and again. Last time I got grease, I got Mobil One grease hoping this would not occur, and it still did. Any thoughts on a grease that would be resistant to this?

 

[Wrehch]

It's called oil seperation and the ASTM standard that rates a grease as to how prone it is to this is ASTM D-1742. Look for a grease with the lowest % of seperation. TRC's Paragon 3000 has a seperation of 0% and I use their 880 Crown and Chassis grease and it has never seperated on me. One 6 gallon bucket of 880 I have had around at home for about 6 years shows no signs of seperation yet.

 

[NYEngineer]

Does grease with a separation of 0, opposed to one that has a small degree of separation perform any differently? Would it be less prone to shearing?

 

[crashz]

It doesn't seem to be related. For instance the TRC 880 CC has a load bearig cappability of 100lbs/in2 where as the Paragon 3000 is 80 lbs. It does seem to be related to the drop point of the grease though.

 

[Wrehch]

crashz - I think you got the spec's mixed up regarding different NGLI grades. Both the 880 C&C and the Paragon 3000 have a Timken OK load of 100 pounds in NGLI #2 and both also have a Timken OK load rating of 80 pounds in NGLI #1.

As far as how seperation and performance the grease with a lower seperation rate would keeps it's consistancy better where a grease that has excessive seperation over time will tend to dry out.

Would it be less prone to shearing? Not sure, that's a good question. I would think that a greases ability to handle high loads would be more important than it's ability to handle shear.