What must be checked regarding the hub oiler?

The hub oiler is a critical component in a vehicle's wheel assembly that requires proper maintenance to ensure safe operation. It must be checked to ensure that it is full of oil and free from leaks. This is essential because the oil lubricates the wheel bearings, allowing them to operate smoothly and reducing friction. Proper lubrication prevents overheating and excessive wear, which can lead to bearing failure and, consequently, wheel detachment or brake issues while driving.

If the hub oiler is empty, it could indicate a serious problem, such as a potential breakdown due to insufficient lubrication. Having minor leaks does not meet the safety standards required for a successful pre-trip inspection, as it can lead to a decrease in oil levels over time, thus compromising the hub's functionality. Furthermore, being half full is also inadequate, as it may not provide sufficient lubrication to the bearings. Therefore, ensuring that the hub oiler is both full of oil and leak-free is vital for the safe operation of the vehicle.