Symptoms of Bad or Failing Differential / Gear Oil

Modern vehicles use a variety of fluids for the lubrication of their numerous mechanical components. Since many of the components are made of metal, they require heavy-duty oil capable of protecting the components from damage due to overheating and metal-to-metal contact. Automotive lubrication fluids play a very important role in the overall performance and service life of a car and can cause components to become seriously damaged when they run low.

One of these types of fluids is the differential oil, also commonly known as gear oil, which is used to lubricate manual transmissions and differentials. Since gear oil is basically the equivalent of what engine oil is to the engine, it plays a very important role in protecting the differential and transmission, allowing them to do their jobs safely and smoothly. When the fluid gets dirty or contaminated it can put the components that it is meant to protect at risk of accelerated wear and even permanent damage. Usually, bad or failing differential oil will produce any of the following 4 symptoms that can alert the driver of a potential problem that should be serviced.

1. Vehicle Exceeds Gear Oil Service Interval

All vehicles come with a maintenance schedule for its fluids and filters based on mileage. If the vehicle has exceeded the recommended mileage for service of the gear or differential oil, it is highly recommended to have it changed. Old oil may not provide the same level of protection as clean, fresh oil. Vehicle components run using old or dirty oil may end up susceptible to accelerated wear or even serious damage.

2. Whining Differential or Transmission

One of the symptoms most commonly associated with bad or failing differential or gear oil is a noisy transmission or differential. If the gear oil runs low or becomes excessively dirty, it can cause the gears to whine or howl as they turn. The whining or howling is caused by lack of lubrication and may increase in volume as vehicle speed increases. A howling or whining differential or transmission should be inspected as soon as possible in order to prevent the possibility of serious damage.

3. Gearbox/Transmission Slipping Gears Jerking

Though a jerking transmission can be caused by a number of potentially expensive issues, it can also be another sign of low gear oil levels. The differential or gear oil may be in need of replacement after reaching levels too low for proper operation of the transmission. Check your transmission fluid levels to see if the reservoir is too low and causing gears to grind and slip. If topping off oil levels doesn’t fix the problem, have your transmission system inspected — it could be a sign of a more serious problem.

4. Burning Smell from Gearbox or Differential

A burning smell from your differential or gearbox is another sign you need near differential oil. The smell may be coming from oil leaking out of an old seal — you may even notice a reddish stain under your car’s parking spot. The burning smell might also be a result of an overheating gearbox from poor lubrication. Too-old oil cannot lubricate moving parts properly, causing the metal components to burn oil from the high temperature. Having the differential oil replaced may solve the problem, otherwise, a gasket or seal replacement may be necessary.

Differential/gear oil is just one of the many important lubrication fluids that vehicles use in their normal operation. However, it is often one of the most forgotten fluids because it is not serviced nearly as frequently as others. For this reason, if you suspect that your differential or gear oil may be dirty, contaminated, or past the recommended maintenance schedule, have the vehicle inspected by a professional technician. They will be able to replace your differential / gear oil if necessary.


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