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Greases have different
type of complex's that holds the oil and additives. What happens is that
most common off the shelf greases you see is a lithum complex type of
grease that says "water resistant".
Most people think that bearings having seals will prevent water from
getting into the bearing, when in fact it is really there to hold the
grease in. Look at how the lip is on the seal, it's cupped inward not
outward.
When you have a hot bearing, exposed to cold water, (through a mud puddle
or in the boat ramp) the hot bearing will cool down fast and suck in
moisture.
Lithium is a soap type complex, and soap emulsifies (mixes) with water.
When this happens, the grease starts to turn milky, and will thin out,
then after a period of time sling out of the bearing. It makes no
difference if it's a synthblend or full synth oil in the grease, if the
complex washes away with water, the oil goes with it, not leaving anything
to lubricate.
Can this be avoided? Yes, an aluminum complex will not mix and in most
cases will say WATER PROOF. BEWARE! I have seen greases that said water
proof on them and in fact were lithium based and also turn milky. So read
the label and look at the complex being used.
Another thing you can do is take a dab of grease, put into the palm of
your hand, add some water, and mix with other hand, if it doesn't thin out
and mix, your on the right track.
click on the pics to see
demonstrations of lithium and alum complex
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