I now understand why I shouldn't have asked about trailer bearing grease in another thread (both for my technical understanding and buckets of carp quoted on the internet "I have used brand x for years in low speed bearings so it will be absolutely fine in high speed, high temperature salt water exposed bearings etc")!
From other searches "Grease is a mixture of a oil, base thickener and additives like tackifiers, graphite, moly, teflon, dye, etc. It is the base thickener that may be incompatible with another greases base and creates a black runny mess that lets your bearings fail. It matters little whether the oil is conventional or synthetic."
I have found a few tables to indicate whether adding a different type of grease into bearings will cause the resulting mixture to stop working as a lubricant:
- Lithium or lithium complex base is the most common, and is moderately waterproof.
- Aluminum complex is much more waterproof and most are compatible with lithium.
- Calcium sulfonate complex grease is more water resistant than an aluminium complex"
So digging around the specification sheets for both heavy duty and marine greases, it appears that the vital specifications are around:
- Dropping point (effectively at what temperature the grease turns to a non lubricating liquid - higher seems better)
- 4 ball weld point (higher is better)
- Load index (higher is better)
- Timken OK Load (higher is better)
- Base oil viscosity (lower is better?)
Needing some real world examples I found quite a few places sell the Lucas X-Tra Heavy Duty Grease for use in trailer bearings (which I currently use).
I have now found Lucas Marine Heavy Duty Grease which appears to be Calcium Sulfonate based and has a low water washout, high weld point (500kg) and higher dropping point (turns liquid at over 300C) than many others.
The gold standard grease that TrailerGuy uses I think is the Grade 2 5517 Castrol Pyroplex Blue which is a lithium complex grease, but it looks like the Lucas calcium sulfonate grease may have the edge on this - are there any tribologists out there who could offer expert views?