You know how often to change your engine oil; but what about the gear oil in your standard shift transmission? Here’s a short guide, from Alvie's Transmission Service Unlimited in Jacksonville. Unless you’re lucky enough to own a car with a transmission dipstick, inspecting the gear oil in a manual transmission is a lot more inconvenient than doing so with an automatic, or checking your engine oil. The car must be jacked up, supported, and the oil checked from underneath. As a result, you may just want to change it when the time is right. But how do you know when that time comes?