What Causes a Crankshaft Seal Leak? (Symptoms & Solutions)

The crankshaft seal plays a crucial role in the functionality of an engine, preventing oil leakage and maintaining optimal performance. However, over time, these seals can develop leaks, leading to various issues and potential damage to the engine.

In this article, we will explore the common causes of crankshaft seal leaks, identify the symptoms of a leak, and provide a step-by-step guide on how to fix it. By understanding these factors, you’ll be better equipped to address this problem and ensure the longevity of your engine.

Understanding the Crankshaft Seal

Before delving into the causes and solutions for crankshaft seal leaks, it’s important to grasp the basics of this component. The crankshaft seal is located at the front or rear of the engine, depending on the design. Its primary function is to prevent oil from escaping the crankshaft and leaking into other parts of the engine. By maintaining a proper seal, the crankshaft can rotate smoothly without any friction-related issues.

There are two main types of crankshaft seals: front seals and rear seals. The front seal is situated at the front of the engine, behind the harmonic balancer or pulley, while the rear seal is located at the back of the engine, near the flywheel or flexplate. Both seals serve the same purpose but differ in their placement within the engine.

Common Causes of Crankshaft Seal Leaks

Several factors contribute to crankshaft seal leaks. Understanding these causes will help you address the issue more effectively. Here are the most common reasons for crankshaft seal leaks:

Wear and Tear

One of the primary causes of crankshaft seal leaks is natural degradation over time. The continuous rotation of the crankshaft, exposure to high temperatures, and contact with oil and debris can wear down the seal’s material.

Consequently, the seal loses its ability to maintain a proper seal, resulting in leaks. Additionally, engines with high mileage or prolonged usage are more prone to seal wear and tear.

Poor Installation or Maintenance

Improper installation and inadequate maintenance practices can also lead to crankshaft seal leaks. If the seal is not installed correctly, it may not fit snugly against the crankshaft, creating gaps for oil to escape.

Furthermore, insufficient lubrication during installation can cause the seal to wear out prematurely. Neglecting regular maintenance, such as oil changes and seal inspections, can also contribute to seal deterioration and eventual leakage.

Also Read: How Long Do Subarus Last? (Real Life Experiences)

Symptoms of a Crankshaft Seal Leak

Crankshaft Seal Leak

Identifying the symptoms of a crankshaft seal leak is essential for prompt detection and repair. Here are the most common signs to watch out for:

Oil Leaks

The most evident symptom of a crankshaft seal leak is the presence of oil stains or drips underneath the engine. You may notice oil accumulating on the ground after parking your vehicle for an extended period. Additionally, a distinct burning oil smell may be noticeable, particularly when the engine is running.

Engine Performance Issues

Crankshaft seal leaks can impact the engine’s performance. As oil escapes, the lubrication necessary for smooth operation decreases, leading to decreased power or acceleration. You may notice a lack of responsiveness when accelerating or a general decrease in engine performance. Engine misfires and rough idling are also common symptoms of a crankshaft seal leak.

Excessive Smoke from Exhaust

If a significant amount of oil leaks into the engine’s combustion chamber, it can result in excessive smoke coming from the exhaust. The smoke may appear bluish-gray in color and is typically accompanied by a burning oil smell. This symptom indicates a more severe crankshaft seal leak that requires immediate attention.

Oil Contamination

A crankshaft seal leak can lead to oil mixing with other fluids in the engine, such as coolant. This contamination can be identified by observing the oil or coolant reservoirs. If you notice oil in the coolant or vice versa, it is a strong indication of a crankshaft seal leak that needs to be addressed promptly.

Steps to Fix a Crankshaft Seal Leak

Once you have identified a crankshaft seal leak, it’s crucial to take prompt action to prevent further damage to your engine. Here is a step-by-step guide to fixing a crankshaft seal leak:

Step 1: Diagnosing the Leak

Begin by visually inspecting the engine for oil stains or drips, focusing on the front or rear of the engine depending on the seal location. Additionally, you can utilize specialized tools like UV dye to identify the source of the leak more accurately.

Step 2: Necessary Preparations

Gather all the required tools and a replacement crankshaft seal before starting the repair process. Ensure you have the correct seal for your specific engine model. Additionally, take safety precautions such as disconnecting the battery to avoid any electrical mishaps.

Step 3: Removing the Damaged Seal

To access the crankshaft seal, you may need to disassemble certain engine components. Follow the manufacturer’s guidelines or consult a repair manual for your specific vehicle to ensure proper disassembly. Once you have reached the seal, carefully remove the old seal using appropriate tools.

Step 4: Installing the New Seal

Prepare the new crankshaft seal for installation by ensuring it is clean and free from any debris. Apply a thin layer of oil or grease to lubricate the seal and make the installation process smoother. Take care not to damage the seal during installation and ensure it fits snugly against the crankshaft.

Step 5: Reassembling Engine Components

After successfully installing the new crankshaft seal, reassemble all the engine components you previously disassembled. Make sure to tighten all bolts and connections to the manufacturer’s specifications. Double-check that everything is in its proper place before proceeding.

Step 6: Testing for Successful Repair

Start the engine and closely monitor for any signs of leaks. Check for oil stains or drips underneath the engine and inspect the seal area for any oil seepage. Additionally, monitor the engine’s oil pressure and overall performance to ensure the repair was successful.

Prevention and Maintenance Tips for a Crankshaft Seal

While fixing a crankshaft seal leak is crucial, preventing such issues in the first place is equally important. Here are some preventive measures and maintenance tips to minimize the chances of crankshaft seal leaks:

Regular Oil Changes

Follow the manufacturer’s recommended oil change intervals and use the appropriate oil type for your engine. Regular oil changes help maintain proper lubrication and prevent premature seal wear.

Inspecting and Replacing Worn Seals

Include crankshaft seal inspections in your routine maintenance checks. If you notice any signs of wear or deterioration, promptly replace the seals to prevent leaks and further damage.

Proper Installation Techniques

Ensure the crankshaft seal is installed correctly during repairs or engine rebuilds. Refer to the manufacturer’s guidelines or consult a professional to guarantee proper installation and prevent future leaks.

Maintaining Optimal Engine Temperature

Extreme temperatures can accelerate seal degradation. Ensure your engine stays within the recommended temperature range by maintaining the cooling system, including the radiator, hoses, and thermostat.

Following Manufacturer’s Guidelines

Always follow the manufacturer’s guidelines and recommendations for maintenance, including oil specifications, service intervals, and inspection procedures. Adhering to these guidelines will help prevent crankshaft seal leaks and other engine-related issues.

Also Read: Transmission Cooler Lines Leaking At Radiator (Causes & Solutions)

Frequently Asked Questions

How serious is a crankshaft seal leak?

It is common for your car to leak oil, and this is often a sign of something bigger going on. In older Minis, oil leaks are commonly caused by worn, broken, and cracked crankshaft seals. In the case of an unattended broken crankshaft seal, major engine problems can arise.

How do you know if your crankshaft is broken?

There can be a banging sound from your engine, or a warning light may indicate low oil pressure (on the gauge or in the instrument panel). If the situation gets severe, the engine won’t run at all. You should stop your car immediately after noticing any of these symptoms. There is no need to continue driving it.

How much does it cost to replace the crank seal?

Front crankshaft seals are simpler to change than rear ones, with the replacement prices starting from about $200 and stretching up to about $500 and above; this depends on the car plus the engine design.

How long does it take to replace a crankshaft seal?

For an initial but approximate estimate, the seal on its own typically costs $20-$25. The labor for your car will probably take between 2 and 3 hours, depending on whether you have a double cam or single cam engine.

How long do crankshaft oil seals last?

It has been mentioned above that crankshaft seals last for around 100,000 miles on average. The time has come to replace your crankshaft seal if the odometer on your car is approaching that number!

Is it hard to replace the crankshaft seal?

Seal replacements can be difficult, especially for transverse engines, meaning engines equipped with front wheels or all wheels. Relative to what must be removed to remove the engine cover, replacing the seal on a rear-wheeled driven car may be simple or hard.

Do you have to drain oil to change the crankshaft seal?

There is no need for it. The sump doesn’t get very high, so the oil does not overflow. In addition, oil pumps are located between the sump area and the seal.


Crankshaft seal leaks can be a common problem in engines, but with timely detection and proper repair, they can be resolved effectively.

By understanding the causes and symptoms of crankshaft seal leaks, you’ll be better equipped to take the necessary steps for fixing and preventing them.

Remember to perform regular maintenance checks, follow proper installation techniques, and address any signs of seal wear promptly. By prioritizing the health of your engine, you’ll ensure its longevity and reliable performance for years to come.

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