What do you actually check on a pre-trip inspection?

Better start another thread!

 

You should be able to see the oil threw the sight. Sort of a no brained if you really think about it.

 

Just saying, if you can’t tell the difference between grease and oil, you have no business messing with the hubs on your vehicle! 15+ pages of didactic details, and you’re still going in circles. Oil is runny, grease isn’t. End of discussion. Maybe we should get a thread on here on how to tell the difference between grease and oil lol

 

Really? In ten years you've never seen it?

 

Just check for leaks inside and outside and carry on. Consult your maintenance department for any leaks if you're not sure whether it's bad enough to be concerned. DOT will not be quizzing you.

Whatever form of lubrication will not magically evaporate without a leak, so no leaks, you're probably fine.

 

Some people are slow learner's ..
That's why there's short buses,
and Special Ed classes

 

If you hub covers look like this they are oil filled. after sitting a few minutes the oil will be sitting in the bottom of the hub cover and hopefully somewhere between those lines. sometimes shining a flashlight at the helps to see the oil level.
The hubs cover you showed earlier and from what you described I would say is grease filled. But heck if you've made it 10 years trucking without knowing why worry now