What Causes a Crankshaft Seal to Leak: Top 6 Causes

We will explore the causes of crankshaft seal leaks in this article. Engines have a small, but very important component called the crankshaft seal.

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Its job is to keep the oil in and outside contaminants out. It prevents your engine from losing lubrication and causing it to wear down faster. So what causes it to leak? Here’s what you need to know!

The Crankshaft Seal

In the engine, rotational movement is converted into linear motion by the crankshaft. On the front of the engine is the crank pulley, which is attached to the crankshaft. Likewise, a flywheel (or flexplate) is located on the rear side of it.

Two seals prevent oil leaks, one at the front of the engine and one at the rear, also known as the rear main seal.


What Causes a Crankshaft Seal to Leak

Seals have to be constantly in contact with the housing from which they seal. Due to your engine’s constant rotation, a certain amount of friction will occur over time that causes wear to your engine.

Wear and tear are the most common causes of crankshaft leaks. If your car has already logged 100,000 miles, then the seals around the crankshaft are probably close to failure. Also, the material of a crankshaft seal can affect whether it leaks. 

Seals can wear faster than usual if they are softer or more sensitive than others.


There are 6 possible causes of crankshaft seal leakage:

Additionally to wear and tear, your seals can leak for a variety of reasons. Let’s take a look:


Wear and tear due to high mileage

Crankshaft seals are usually good for 100,000 miles or more. Don’t wait if you’re nearing that number on your car’s odometer and you need a new crankshaft seal! Manufacturers recommend an interval between services. Due to how hard it becomes after extended use, however, replacing near this point can extend its life considerably.


The engine has too much oil on the inside

This is a problem if your engine is overloaded. If there isn’t enough room for oil, too much will leak out of the crankshaft seal. A lack of lubricant will cause the engine to wear out quickly. There may be leaks elsewhere as well.


The seal was not installed properly

An integral part of the crankshaft is the crankshaft seal. You need to properly install it before putting your car back on the road. The improper installation of the oil can cause leaks and shortages of oil around the engine, causing it to function improperly.


A problem with the gasket

You can leak oil from the crankcase and/or from the outside if you have a problem with your crankcase gasket. This is caused by an external force forcing the oil out.


The seal was damaged during a rebuild

Taking the crankcase out of a car without damaging large parts inside, such as the crankshaft seal, is difficult. Then you put it back in improperly if it is damaged when you take it out. There’s little chance of avoiding leakage completely.

There’s been a collision

Seals that have been compromised by impact or other serious damage while driving will leak. They will eventually stop working entirely. If this happens, you may have to pay for expensive repairs later on.

Symptoms of a Bad or Failing Crankshaft Seal

The car’s engine will start to make a humming noise

It is possible to hear a humming noise from the engine that won’t stop if you have a problem with the seal. Symptoms of an oil leak include excessive oil use, black smoke coming from the exhaust pipe, and damage to your driveway or garage floor.

Oil seeps out of the seal when it has been in contact with air

A leaky engine will stain your driveway, tarnish your engine, and turn your car into a junker.

You may see oil seeping from the crankcase seal if your car has been sitting with the engine off for at least a day. This indicates that there is some damage inside your car. Drying out the seal should not be allowed. If something fishy is happening, call for help right away. There could be long-term consequences.


You’ll notice oil leakage on your driveway, or worse, underneath your vehicle’s engine


In case of damage, a crankcase seal leak will result in a steady accumulation of oil under your car. Almost always, this means that something needs to be replaced – and fast. You should not drive your vehicle until this has been fixed, or you risk damaging other parts of the engine.


Oil seeps out at regular intervals

You may notice oil leaking steadily but infrequently (instead of all at once) if you have problems with the timing chain system on your engine. Those leaks aren’t as serious as those caused by leaks in the crankcase. However, they can have an impact on the engine’s performance nonetheless. Schedule an appointment right away!

Inside the car’s engine compartment, there should be some kind of stain where the seal is located


Seals that do not leak oil on their own may absorb oil from other parts of the car. An auto repair shop should be contacted as soon as possible if there is an oil smear in that area.

A greasy/oily smell comes from the seal when it is heated

An overused crankcase seal will give off a “hot” smell like hot metal when it begins to cool down after being used excessively. You might be able to recognize the scent if you know what to look for. The smell will disappear after a few minutes. As long as you haven’t noticed any leaks around the engine before – there’s no need to worry.

It is also possible that you will experience lower gas mileage or a loss of power in your vehicle

Starting your car when the crankcase seal isn’t holding pressure will lead to oil leakage. After that, there will be nothing but an oily residue inside it, and it will go on the engine. As soon as this begins to happen, your car is losing clean air by the minute. Additionally, you’re going to experience problems with gas mileage and overall power. This is because less fuel is burned per mile.



Engine seals wear out over time, and are an important component of your engine. What causes a crankshaft seal to leak is usually wear and tear. 

The seal won’t hold up for more than 100,000 miles. It will start showing signs of wear. The seal will eventually fail. You should take your car to a mechanic as soon as possible if you see excessive oil leaks, either near the crankcase seal or throughout the engine. 


They will be able to pinpoint where the leak is coming from and fix it for you – or at least point you in the direction of someone who can do that kind of work for you.

To keep your car in shape. Don’t forget to do the basic car maintenance at recommended intervals.

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