Many smaller gearboxes have a fill hole and a drain plug. The only way to tell if the gearbox has the proper amount of oil is to unscrew the fill plug and stick your finger in it. To improve this process, replace the drain plug with a sight glass. This makes it easy for anyone walking by the equipment to notice if there is a problem with insufficient oil.
At the same time, because you no longer need to open the fill cap regularly, replace it with an appropriate breather or quick connects (on both the fill port and drain) to add oil or deploy off-line filtration.
The main factor that limits the use of mineral oils in high-temperature applications is their oxidation stability, rather than the viscosity thinning or thermal stability. In the presence of air, it is generally not advisable to use mineral oils in any application at temperatures above 200 degrees F (93 degrees C).
When a leak occurs, look for things that may have created it. Leaks are often caused by pressure buildup. Check for plugged vents, overfilling and elevated heat levels. Stress from too much torque can cause gasket failures that lead to leaks.
Although it is sometimes overlooked, equipment owners should always specify the grease to be used by the companies that rebuild motors (and other equipment with greased bearings) for them. Otherwise, the grease they use may be incompatible with the grease the owner will use to replenish the bearing lubricant. It would be time well spent to visit a frequently used shop and ask someone on the shop floor to show you how he or she knows which grease to add to your equipment bearings.
The presence of sludge in hydraulic oil can significantly reduce the service life of the oil. For example, with 1-percent sludge in an inhibited hydraulic oil, service life is reduced by nearly 40 percent.
If you are having problems with water contamination in outside gearboxes, consider the following:
When it comes to wear-metal trending, it is a mistake to sample downstream of filters. This allows important data to be stripped from the oil prior to sampling.
Another improper common practice is sampling large centralized reservoirs such as those on steam turbines, paper machine lubes and hydraulic systems. The large volumes of oil in these tanks will dilute wear-metal concentrations to levels often below instrument detection limits. Sampling live-zone return lines and bearing drain headers is greatly preferred.