Car Issues and Fixes

Rear Main Seal Leak – Warning Signs and Causes

Avatar Adie Tinkle -

Rear main seal leak can be caused by several factors, and understanding them is crucial. If you think something is wrong with the crankshaft seal, you must take your vehicle to an expert as soon as possible to avoid critical damage. 

Identifying the Causes of Crankshaft Seal Leak

Many factors contribute to the crankshaft rear main seal leak, including: 


Like any other engine component, the crankshaft seal undergoes wear and tear over time. It can lead to gradual degradation in its quality and the seal’s effectiveness, causing it to fail. With time, the engine ages, and the crankshaft seal becomes susceptible to wear and damage due to constant heat exposure, friction, and other environmental factors. 

The oil circulating through the engine can also cause seal degradation, as it contains contaminants and other particles that can wear down the seal over time. When the crankshaft seal is damaged or worn, it can no longer keep the oil inside the engine effectively.

Improper Installation: 

Installing a crankshaft seal is an important process that requires great care and precision. One of the prime reasons a crankshaft may not be installed correctly is damage during the installation process. 

If the seal is dented or scratched during installation, it will not create a tight seal, causing the oil to seep out. That is why ensuring that the seal is not damaged during installation is crucial. 

Using the wrong type of seal for your engine can also cause the crankshaft seal to fail. Different engines have different requirements, and the use of the wrong seal can lead to various issues, such as oil leakage. 

Therefore, it is essential to identify the correct seal for your engine to ensure it functions effectively.  The wrong type of seal can lead to premature wear and tear, causing the seal to fail earlier than anticipated. 

Poor Maintenance

Not maintaining the engine in time can cause the crankshaft seal to deteriorate quickly. Other factors that can contribute to premature seal wear and damage include failure to change the oil regularly, using low-quality oil or oil filters, and not replacing the damaged or worn parts.

High Mileage 

If you own a high-mileage vehicle, it is important to watch for the signs of a leaking crankshaft seal. With higher mileage, the chances of your crankshaft seal leaking also increase. This is because the seal is used for an extended period, leading to wear and tear on its components. 

Symptoms of Rear Main Seal Leak 

Here are some of the primary signs indicating a crankshaft seal leak 

Oil Puddles Under Your Car

One of the primary symptoms of a leaky crankshaft seal is the formation of oil puddles under your vehicle. These puddles can form stains on your parking lot, garage, or driveway. If the oil leaks from a damaged crankshaft seal, it will be dark and thick with a burnt smell. 

Burning Oil Smell 

If you observe a sudden string-burning smell coming from your car, it is also a sign of a severe crankshaft oil leak. Oil leaking into the exhaust or engine forms a distinct smell. This smell is pretty strong as the oil burns on hot engine parts because of the leak. 

If the leaking oil also comes in contact with the hot exhaust system, smoke will come from the hood, and the exhaust system will burn the oil. If you notice any of these signs, take quick action because severe leaks will not only cause damage to the engine but can also lead to potential fire hazards. 

Engine Overheating and Performance Issues

Along with other symptoms, a severe leak can also cause damage to various engine components, leading to expensive repairs. 

Oil leakage can damage the timing belt or chain. A timing belt synchronizes the movement of the engine’s pistons and valves. A broken timing belt can cause irreversible damage to the engine, requiring a complete replacement. 

Similarly, oil leakage can also cause damage to the water pump. These pumps circulate coolant throughout the engine to prevent overheating. If engine oil comes in contact with the water pump seal, it can cause it to wear out prematurely, leading to a coolant leak and potential engine damage. 

Moreover, a rear main seal leak can damage electrical components such as the starter motor or alternator. These components are critical to starting and running your engine. If they are damaged, you must spend additional money on their fixes. 

How to Fix Leak in Crankshaft Seal?

You can fix the crankshaft seal leak by getting an immediate replacement to avoid any more issues. Taking the vehicle to a mechanic who can fix and replace the seal is important. It is also important to ensure proper vehicle maintenance to prevent future problems. 

Regular Maintenance 

Ensuring regular maintenance and proper installation are the keys to preventing future leaks in the crankshaft seal. Not paying attention to regular oil changes or not replacing worn-out parts can cause wear and tear on the seal, leading to leakage.

Therefore, it is important to follow a proper schedule to keep your vehicle in good condition. Moreover, installing the seal properly ensures that it functions optimally without any leaks. 

Replace the Leaky Crankshaft

Replacing the leaky crankshaft is an efficient solution to stop oil leaking from the engine. Though it is a common repair, it requires expertise and careful attention to prevent damage to other engine components. Use the correct seal for your engine and ensure that it is installed correctly. 

Replacing the crankshaft involves removing the timing belt or timing chain. It also involves dissembling other engine components, including harmonic balancers or pulleys. If other components have faced damage because of the seal, they might also require a replacement. 

It might be challenging to do this task on your own unless you have good knowledge of the engine’s anatomy. It is preferable to take the service of a professional mechanic to perform the job correctly.

The cost of crankshaft replacement can vary depending on the make and model of the vehicle, the type of seal, and the extent of damage caused by the leak. 

Professional Help 

Whether you are replacing or repairing the crankshaft, it’s preferable to seek assistance from a professional, as they have expertise and proper tools. They can also diagnose the issue easily and fix it promptly. Taking your vehicle to a professional mechanic can ensure that your vehicle is in good hands. 


In conclusion, identifying the symptoms of a crankshaft rear main seal leak early can help prevent significant damage to your engine and ensure the protection of other components. If you observe that something is wrong with the seal, it is important to take immediate action.

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