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6 Signs Of A Transmission Fluid Leak (+ Causes, Costs & FAQs)

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Is your transmission fluid level constantly low? 
Or are you finding it difficult to change gears? 

If so, you might have a manual or automatic transmission fluid leak. When left unchecked, transmission fluid leaks 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? 

Let’s explore these aspects, including how to diagnose the issue, transmission repair costs, and other related FAQs.

This Article Contains:

Let’s begin.

6 Signs Of A Transmission Fluid Leak 

Let’s explore some common transmission fluid (a.k.a transmission oil) 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 may have red coolant — so how can you tell the difference between a transmission fluid leakage and a motor oil 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, and if it’s dark red fluid, it’s your transmission fluid leaking. 

2. Low Transmission Fluid

It’s a good idea to observe the transmission fluid level closely after topping it up, as a rapid drop could signify a leak. Moreover, checking your transmission fluid level regularly 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 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 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 turn the Check Engine Light on your dashboard (or both) if it detects major transmission performance issues like:

When this happens, you’ll 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 what the signs of a transmission fluid leak look like, let’s see what causes it. 

5 Causes Of A Transmission Fluid Leak 

The transmission system comprises many critical components, so there are many reasons why your transmission fluid leaks.

Here are five 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 debris on the road while driving. This 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 not being 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.

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

Tip: Try stop-leaks like Bars Leaks or BlueDevil transmission sealer to help restore broken rubber seals.

3. Faulty Transmission Pan Gasket

A transmission fluid 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, 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.  

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

Transmission Fluid Leak Repair Cost 

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

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

Transmission Fluid Leak: 7 FAQs

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 components.

2. What Are The Types of Transmission Fluid?

The three types of transmission fluid include: 

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 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. 

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 mechanic. 

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

Final Thoughts

Identifying a leaking transmission early can prevent transmission failure and save you a lot of 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 RepairSmith.

With RepairSmith, 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 all your automotive repair needs.