Shop Talk Logo

How to Identify a Transmission Fluid Leak

Most car owners who drive vehicles with an automatic transmission understand the vital role that this part plays in the vehicle’s overall function, even if they don’t know exactly how and why it works. Transmission repairs tend to be some of the more costly maintenance work car owners encounter, but they are far less expensive when the problem is caught before a major failure. The key is understanding how and why transmissions leak, and also how to diagnose a transmission fluid leak.

Identifying the Fluid

If you have never seen transmission fluid before, it is a bright red substance that runs a bit thinner than engine oil but a bit thicker than brake fluid (in general). It acts as a multipurpose lubricant and hydraulic solution, and it’s also designed to condition seals and gaskets so they last longer.

Finding a Leak

Some vehicles still have ways of assessing the transmission fluid level in the system, but many more recent models have been designed with closed systems. Either way, there is a simple diagnostic confirmation that will tell you if your vehicle is leaking transmission fluid. You just have to check for stains underneath. Find someplace clean and level, so your vehicle and engine rest naturally and you don’t have to worry about other fluids or previous stains interfering. Then follow these steps:

  • Lay out a clean drop cloth underneath the vehicle’s parking space.
  • Park on top of it, centering the cloth as much as possible and making sure the entire engine block and transmission are over it.
  • Leave the vehicle off and parked overnight.
  • Check the cloth for stains.

Leaks are often at the sites of gaskets and seals, which means that they might not be apparent while the level of fluid in the pan is low. After the car stops, lubricating fluid drains out of components and back to the pan, just as it does with engine oil. As the pan level rises and other parts near the bottom of your transmission also get coated in fluid from the pan’s reservoir, previously unseen leaks can appear.

Diagnosis: Positive

If you find leaks of a bright red fluid, it likely confirms the diagnosis of a transmission fluid leak. Some manufacturers will use transmission fluid in power steering systems as well, so once you find a leak, you should talk to a certified technician about identifying its exact source and enacting a repair. The sooner you do, the easier it is to contain any issues.