Along with your engine, your car's transmission is an incredibly expensive part to replace. It's important to monitor its condition and have it checked out as soon as you notice any warning signs that it is failing. 

One of the most common sources of transmission failure is overheating—when your transmission gets too hot, the soft components of your transmission, such as the gaskets, begin to burn and rapidly deteriorate. If you don't stop your transmission from overheating, it will rapidly degrade until it fails completely. To help you protect your transmission from overheating and your wallet from expensive transmission replacement costs, here are four common signs of an overheating transmission.

1. There's a Sweet Smell Coming from Your Transmission

Transmission fluid has a distinctive sweet odor. When your transmission overheats, the smell becomes much more noticeable. If you notice a sweet smell while driving around, it may be a sign of an overheating transmission. If your transmission has been overheating for a while and some of its components—such as the gaskets—have started to burn, you may also smell a slight burning odor. These strange odors coming from your car's hood are a sign that you need to take your car to a transmission repair shop and have your transmission inspected.

2. Transmission Fluid Is Bubbling Out from the Top of Your Transmission

Transmission fluid expands significantly when it heats up. After driving around in your car for twenty or thirty minutes, check underneath your hood and look at the vent on the top of your car's transmission. If you have difficulty finding it, your owner's manual likely has a diagram you can refer to in order to locate your transmission. When your transmission fluid expands due to overheating, you'll see a small amount of it bubble up from the vent on your transmission.

3. Your Transmission Fluid Is a Dark Color

The color of your transmission fluid can tell you whether or not your transmission has been overheating. Open your car's hood, pull out the transmission dipstick, and wipe it on a white surface like a paper towel in order to inspect the color. New transmission fluid is bright and transparent, but transmission fluid from an overheating transmission will be opaque with a dark brown color. The dark color is caused by small particles of burnt gaskets or bands flaking off into your fluid, and it's a sign that your transmission is in critical condition and that you should take your vehicle to a transmission repair shop as soon as possible.

4. Your Transmission Is Slipping, Especially After Driving for a Long Period of Time

When your transmission becomes too hot, it's more likely to slip. Slipping occurs when your transmission is unable to shift gears properly. You can tell that your transmission is slipping gears when you're revving the engine without any noticeable increase in speed.

Slipping is most apparent when you first accelerate after stopping at a red light—no matter how hard you press down on the gas pedal, you'll experience difficulty accelerating for a few seconds after your automatic transmission attempts to shift into second gear. If you have trouble accelerating after you've been driving for a while, your transmission is likely overheating.

If you notice any of these signs, schedule an appointment at a local transmission repair shop. Every time you drive your car with an overheating transmission, you're doing more damage to it. Fixing the source of the overheating as soon as possible will ensure that your transmission is kept in good condition and isn't at constant risk of failure.