Do You Have a Transmission Fluid Leak? 6 Signs & Causes

Transmission leaks are the automotive equivalent of a ticking time bomb, silently sabotaging your beloved vehicle.

When left unchecked, a manual or automatic transmission fluid leak can cause complete transmission failure, potentially leading to accidents or breakdowns.

But how can you tell if you have a transmission fluid leak?
And what causes it?

In this article, we’ll demystify transmission leaks — unraveling the causes, warning signs, and potential costs of fixing this automotive predicament. We’ll also answer a few FAQs so you’ll have a wider picture on transmission fluid.

This Article Contains:

6 Warning Signs of a Transmission Fluid Leak
6 Potential Causes of a Transmission Fluid Leak
Transmission Fluid Leak Repair Cost
7 FAQs about a Transmission Fluid Leak

Let’s begin.

6 Warning Signs of a Transmission Fluid Leak

Let’s explore some standard transmission fluid leak signs:

1. Red Fluid Under Your Car

Found a red puddle underneath the front or middle of your car?
It could be a sign of your transmission fluid leaking.

But some cars use red engine coolant — so how can you tell the difference between a transmission fluid leak and an engine coolant leak?

It’s simple:
Transmission fluid turns dark brown or black like engine oil over time, while coolant remains unchanged.

So, if you spot bright red fluid, it’s most likely a coolant leak. If it’s dark red fluid, it’s likely transmission fluid leaking.

2. Low Transmission Fluid

Observing the transmission fluid level closely (after topping it up with fresh transmission fluid) is a good idea since a rapid drop could signify a leak. Moreover, regularly checking your transmission fluid level helps prevent transmission issues.

Here’s how:
Use the transmission fluid dipstick to check the fluid levels. If the fluid level is below the minimum marker on the dipstick, you’ll need to top it up with fresh transmission fluid and look for signs of a leak.

3. Rough or Slipping Transmission

A sudden drop in transmission fluid levels (due to a leak) may result in transmission performance issues like rough gear changes or slipping gears.

How can you tell if you have a rough or slipping transmission?
You’ll notice the engine’s RPM (revolutions per minute) climbing as you step on the gas pedal, but the car won’t move as fast.

Sometimes, you may feel jerks when you change gears or find it difficult to engage a gear. However, the latter could also be due to a faulty transmission solenoid.

4. Burnt Smell When Driving

If you have a transmission fluid leak or just a low transmission fluid level, you may notice a burnt smell while driving, especially at high speeds.

That’s because a low transmission fluid level increases friction between the transmission components, eventually leading to overheating and a burning smell.

5. Limp Mode or Check Engine Light On

The Engine Control Unit (ECU) will put your vehicle in limp mode or trigger the Check Engine Light (or both) if it detects major transmission performance issues like:

Overheating
Leaking transmission fluid
Low transmission fluid

When this happens, you’ll likely be unable to go over 30mph and second gear.

6. Humming Sound

A humming sound from the transmission is rare and usually indicates a broken transmission part. Typically, this is caused by increased friction due to low transmission fluid or a transmission leak.

Now that we know the signs of a transmission fluid leak, let’s see what causes it.

6 Potential Causes of a Transmission Fluid Leak

The transmission system comprises many critical components, so there can be many circumstances behind a manual or automatic transmission fluid leak.

Here are the five most common reasons behind leaking transmission fluid:

1. Worn-Out Transmission Pan Or Drain Plug

Transmission components like the transmission pan or drain plug are susceptible to wear and tear.

They could also easily get damaged from loose rock or road debris while driving. This road debris may cause a puncture in your transmission pan or loosen the drain plug or bolts, resulting in a transmission fluid leak.

Sometimes, the leak may be due to the drain plug with a loose bolt, which may not have been screwed back properly after a transmission flush or transmission service.

2. Broken Transmission Seal

The hydraulic pressure in automatic transmission vehicles is sustained through various transmission seals, such as the output shaft seal.

However, your transmission seal may wear out or break if exposed to excessive heat often. It could also happen if you’ve added too much transmission fluid to the system — which could cause a transmission leak.

Furthermore, when a transmission seal like the output shaft seal starts to leak, it also allows debris to enter the transmission system, leading to further damage.

3. Faulty Transmission Pan Gasket

A transmission leak could also occur due to a faulty or damaged transmission pan gasket.

How does this happen?
Your transmission pan gasket could malfunction due to poor manufacturing, bad gasket alignment, a loose bolt, or excessive heat exposure.

4. Damaged Torque Converter

The torque converter pumps transmission fluid into the whole transmission system. A cracked torque converter body or damaged needle bearings will leak transmission fluid.

5. Cracked Fluid Line

The transmission fluid line is made of highly durable steel or aluminum but is susceptible to damage due to debris and overexposure to heat, resulting in fluid leaks.

6. Faulty Transmission Cooler

The transmission cooler regulates temperatures in the transmission lines, preventing transmission damage.

When it’s faulty, the heat in the engine won’t be adequately absorbed, causing the transmission lines to break and burn, leading to a transmission fluid leak.

So, how much do these transmission components cost?
Let’s find out.

Transmission Fluid Leak Repair Cost

Transmission repair (even a tiny leak) can cost anywhere from $10 to $4,500. Here are the average estimated costs of crucial transmission components, including labor:

Drain plug: $10 (excluding labor)
Front transmission seal: $150
Transmission pan gasket: $300 to $450
Rear transmission seal: $600 to $900
Transmission pan: $1,500 to $3,500
Torque converter: $2,000
Rebuilding a transmission: $4,500

Still, have a few questions on your mind?
Let’s look at some common questions related to a leaking transmission.

7 FAQs about a Transmission Fluid Leak

Here are some questions and answers related to a transmission fluid leak:

1. What Is Transmission Fluid?

Transmission fluid lubricates the bearings and other metal components in your car’s gearbox, like how engine oil lubricates the engine’s parts. Like transmission oil, transmission fluid is crucial in ensuring you can shift gears effortlessly.

2. What Are the Types of Transmission Fluid?

The three types of transmission fluid include:

Automatic Transmission Fluid: Automatic transmission fluid may have a clear red, blue, green, purple, or amber color, depending on the manufacturer. Automatic transmission fluid has a thinner consistency than the other transmission fluid types. But, it’s thicker than brake fluid and needs to be changed every 60,000 to 100,000 miles.

Manual Transmission Fluid: A manual transmission fluid is dark in color and has a thicker consistency. Changing the manual transmission fluid every 30,000 to 60,000 miles is best.

Synthetic Transmission Fluid: Synthetic transmission fluid is an engineered product that’s less likely to break down, oxidize, or lose consistency in high temperatures. Synthetic fluid can last for more than 100,000 miles.

Tip: When choosing a transmission fluid for your vehicle, always consider the specifications provided by the manufacturer or consult a transmission specialist.

3. How Do I Differentiate Between Transmission Fluid and Motor Oil?

The easiest way to differentiate between engine and transmission oil is by smell. Transmission fluid has a mildly sweet smell, whereas engine oil has a pungent smell.

4. Is a Transmission Fluid Leak Critical?

Driving with your transmission leaking fluid may not pose immediate concerns. However, leaving even a minor transmission fluid leak unresolved for a long time can lead to severe transmission damage and expensive repairs.

5. Why Does My Transmission Fluid Leak Only While Running?

Typically, this is a sign of a damaged or cracked transmission line.

When the engine runs, the transmission line transports fluids between the transmission and the radiator, to lubricate components properly. If the fluid line cracks, the transmission fluid leaks, which prevents the transportation of fluids, leading to engine damage.

6. Can Transmission Fluid Levels Drop Without a Leak?

Although it’s unlikely, transmission fluid can evaporate over time. But evaporation is usually insignificant and shouldn’t cause a drop in the transmission fluid level.

7. How to Diagnose a Transmission Fluid Leak?

There are many reasons why your transmission is leaking fluid, so it’s best to leave it in the hands of an experienced auto service mechanic.

Here’s how a skilled technician would diagnose the leak:

The auto service mechanic will use a degreaser or brake cleaner to clean your vehicle’s undercarriage.
They’ll do a test drive and then park your car on a cardboard piece.
Next, they’ll use a bright LED-type light to inspect all the transmission components.
If the transmission fluid leakage remains undetected, they’ll use an automotive leak detection kit with a bottle of petroleum-based fluorescent dye, a UV light, and tinted glasses.

Final Thoughts

Identifying a leaking transmission early can prevent transmission failure and save you money. But since diagnosing the problem and cause of transmission fluid leaks is complex, it’s best to consult a reputable auto repair service like AutoNation Mobile Service.

With AutoNation Mobile Service, booking an appointment takes only a few clicks, and our expert technicians will show up in your driveway ready to help.

So, get in touch with us today, and we’ll take care of your transmission service, transmission flush, and any related maintenance procedures.