I see a lot of wheel bearings worn before the due date, and in most cases the hub, where the bearing sits is full of grease, so tightly packed between the outer and inner bearing, how can the bearing have any hope of cooling?

Grease is actually an absorbent of heat, so when you re-pack the wheel bearing, put a smear of grease in the hub, it's an old custom to pack a hub full of grease as we tend to believe that the grease, as it's heated will circulate around the bearing, this is unfounded and simply not true, if you expect  this from a grease then perhaps your thinking of an oil as grease is used as a once only lubrication of the bearing, it should stick to the bearing and the casing or cone even the smear of grease that you apply to the hub will not have any effect on the life of the bearing, the volume between the outer and the inner bearing is used to cool the bearing, this is why when i do a re-pack i can almost count on the bearings being stuffed because it can't cool down due to over grease.

How do you tell a bearing is unservicable and should be replaced? Do a visual inspection after you have removed the bearing and cleaned it , look for grooves on the rollers, look for tarnish of the chrome, some bearings are chrome plated so if the shine is gone, then it should be replaced, also rattle the bearing, if the bearings rattle inside the casings then take that they are worn and should be replaced. Use a good quality bearing such as timkin or skf, these bearings have been proven to withstand harsh Aussie climates, don't always go for the cheapest, i don't do the upsell with my customers, but i won't fit a cheap mass produced part either, i fit the same parts to your car as i would my own.

Whens a good time to look at bearing re-pack? Before or after the wet season in north queensland is a good time, other than that it's going off when the maker of the car recommends to re-pack, a typical 4WD Toyota, Nissan etc every 40k, but it's better to replace regardless if the bearings you are trying to service have already done 40k, depends on the quality of the bearing as well, a timkin or SKF bearing will last a lot longer to a cheap asian bearing, whn i service i always check the 'freeplay in the wheels to determine the wear, if any movement i always recommend a replace. Be carefull as when you have a sealed bearing that requires pressing to install, these bearings do not need grease as they are pre-packed, don't go packig them if no lube is required, this will void your warranty on the bearing!

Always replace the hub seals, always use a good quality grease, Penrite HTB grease is the best i have used, a bit more expensive but you need ultimate protection. The bast way to pack a bearing is by hand as illistrated. Gook luck....... Happy packing!