Tow dolly wheel bearings

If the bearings are packed correctly and the hub area between the races is full you get the best heat dissipation. Air does not dissipate the heat that is expelled from the bearing through the grease packed in to it. I would rather have the hubs full than clean with only grease on the bearings. You will only blow grease out past the seals if you actually fill the hub to the point it pressurizes as temps increase. You want the grease between the races to pull heat from them to the hub. My hubs very seldom run over 110 degrees F but then my trailers have only seen about 100,000 miles over the last 4 years. Having said that, you do need to leave some air space in the hub especially on brake equipped trailers but even if the spindle grabs some grease as you install the hub you will be fine.
Randy

Grease is grease. It all meets NLGI standards.Use NLGI wheel bearing grease and it won't make any difference if it's synthetic. Read the standars.

Bearing Buddies were originally made for boat trailers so there would be no space for water to enter when launching a boat. They were also spring loaded to allow for the cooling when submerged.

Trailer axle hubs are notorious for being ignored, and getting improper maintenance when it is done. So, they put external grease nipples on and people can just pump them full of grease. Yes, the end result is more grease in there than is really needed, but it is better than not enough grease. You can look up the greasing instructions on the axle manufacturers web site or follow the old school rules of thumb - bottom line if you're doing maintenance and do it right, you'll be good to go.

Brian

Too much grease can cause churning of the grease, a build up of heat and blown seals. Unless they get wet as in fording streams or boat trailer yes a good greasing should be good for years if done properly. I do use synthetic grease.
From Timken
"The right amount of grease, How much grease to add to a bearing housing - 1/3 to as much as 1/2 of the housing volumen. Too much (more than 1/2) grease causes overheating; too little causes lack of lubrication. 1/3 is about right."