4 Rear Main Seal Leak Symptoms and Replacement Cost

Here is a straightforward engine part that is crucial to the longevity of your engine. It is so crucial that your engine cannot function properly without it.

Unfortunately, it is frequently forgotten about by automobile owners. Even vehicle repair professionals occasionally overlook it when doing normal maintenance on engines or gearboxes.

For you to understand the significance of diagnosing a leaking rear main seal before the repair becomes more expensive, we will assist you with a tutorial on how to handle a leak in the rear main seal.

The rear main seal is a little rubber or rope-like component in the engine of your car that might cost you a fortune to fix. In the event of a damaged, leaking rear main seal, any driver would not hesitate, preferring to swiftly exit the road and get the automobile replaced as soon as possible.

Your automobile may be leaking oil for a variety of causes, but a broken rear main seal is one of the most serious. If your car has this problem, a significant repair is required. But what signs indicate a leak in the rear main seal?

You could initially see oil spilling onto the driveway. Additionally, as the engine oil is depleting of its vital lubrication, you will need to replenish it. If you look closely, you could see that the underbody is soaked in oil and that the oil warning light is on.

This article touches on rear main seal leak repair techniques and warning signs. It also describes how to mend a rear main seal, the reasons why they fail, and how much it costs to replace a worn-out rear seal.

A Rear Main Seal: What Is It In Your Car?

How does a rear main seal function? What is it? The rear main seal, which prevents leakage from the crankshaft’s back end, is located at the rear of the engine, between the engine and the gearbox. It is a pricey remedy since it frequently necessitates taking the gearbox or engine apart.

Position of rear main seal on the transmission. It hides in the bell-housing of the transmission and is driven into the back cover, making them more difficult to view. Most of the time, it cannot be viewed without removing other important parts, sometimes even the gearbox.

The rear of the engine is the side opposite the one with the idler pulleys, tensioners, and serpentine belts in front-wheel automobiles because the engine is frequently situated diagonally.

Except if you’re a gearhead like me, it’s difficult to identify an engine oil leak from the rear crankshaft seal since the oil often flows from the location where the gearbox links to the engine and then drips somewhere else, like the crankcase.

Typically, silicone or rubber is used to make the rear crankshaft seal. The crankshaft rotational forces, corrosion from road salt, and other environmental variables cause the seal to deteriorate over time. Driving when the rear main seal is leaking can be extremely risky and result in complete engine failure.

What Is the Function of the Rear Main Seal In Vehicles?

The rear main seal is utilized to stop oil leakage from the engine’s back. It maintains the oil in the area where the flexplate or flywheel connects the crankshaft to the vehicle’s transmission. Because of this, the rear main seal is sometimes called the rear crankshaft seal.

The oil in the crankcase may leak if the seal isn’t functioning properly. This issue causes a leak, whose severity can vary.

Where Is the Rear Main Seal Located In a Car?

The automobile engine’s rear is where you’ll find the rear main seal. They can be hidden in the bell-housing of the transmission and are driven into the back cover, making them more difficult to view. Most of the time, it cannot be viewed without removing other important parts, sometimes even the gearbox.

Although the seal is situated at the rear of the engine, this is not always the case. Distinct engines have different faces. The front of the engine is typically facing the front of a rear-wheel or four-wheel-drive vehicle.

On some all-wheel drive and front-wheel drive cars, however, the engine is mounted transversely. The rear of this engine would be off to the other side since the front is facing either the left or right side of the car.

Normally, the rear main seal is placed in the opposite corner from where the belts and pulleys are. Typically, the front of the engine houses these components.

What are the Symptoms of a Rear Main Seal Leak In a Car?

A rear main seal leak is a serious issue. Furthermore, it’s not difficult to determine if a primary seal failure has occurred. You need to know where the rear main seal is located to complete this.

And that is inside the car, behind the firewall. The seal is situated between the flywheel and the back of the engine. The transmission is then linked to the flywheel after that.

So, to access the flywheel and remove it, you must first remove the transmission before doing the same for the flywheel. The rear main seal will then be accessible.

But enough about mechanics; let’s look at how to identify a leaky rear main seal and identify the problem.

Because you need to be certain that the oil leak is coming from the rear main seal at all times. You don’t want to spend money on a replacement rear main seal in vain. So let’s talk about the signs of a damaged rear main seal.

A V6 internal combustion engine by Till.niermann / CC BY-SA 3.0 If you use an oil that isn’t meant for your engine, the rear main seal might easily degrade. In addition, the oils may cause the rear main seal to dry up and stiffen with time, opening the door for a leak.

1. Stains of Oil On the Ground Where the Car Is Packed

If your rear main seal is leaking, oil spots on the ground are to be expected. And if you don’t fix this, these spots will eventually turn into oil pools.

However, you need to be aware that the oil may leak from a variety of locations. Perhaps your oil pan gasket has failed or you have a leaky oil pan. You must ascertain the location of the leak because of this. The angle should be from the engine’s rear.

It is a good idea to leave the automobile parked in the same location for some time to confirm the source of your leaks.

Verify that the vehicle is parked in the same location. If the oil pan is the source of the leaks, the leak ought to be closer to the front of the car. If a rear main seal is at blame, the oil stain ought to be directly on the firewall mark.

Therefore, you must inspect the automobile from below to be certain. You can secure the automobile and hoist it into the air if you have some jacks. You will be able to see clearly where the oil is coming from by approaching the automobile from underneath.

If there is a large spill of oil behind the bell housing, you need to Google “rear main seal replacement cost” right away since this rear main seal has to be replaced. We will talk about that further down the line.

2. Engine Oil Warning Light Illuminates

I learned the majority of what I know about automobiles from older drivers and mechanics, and one of the first things they told me was what to do when the engine oil lamp illuminates. If the dashboard light starts to flash, stop the car as soon as you can and turn off the engine.

You don’t know if a massive gasket rupture has drained your engine of oil in a couple of seconds or if a minute oil trickle has been detected by your current car’s smart sensor. Every engine revolution from the moment the light turns on is crucial because it can be running out of fuel.

If you can, look for oil spills on the road and check underneath the car for greasy parts and leaks. From this point on, the cost of the repairs will depend on how you address the issue.

The safest course of action is to dial roadside assistance and have your car transported to a shop for inspection and repairs. If you opt to overlook the problem because you don’t notice any leaks, you might cause your engine to seize and become scrap metal.

In the end, the decision is yours, but I highly suggest investing in whatever it takes to make sure the engine has enough oil within it.

3. Excessive Loss of Oil

Large oil loss is another sign that the rear main seal is leaking. The loss of oil will increase in severity, particularly if the seal is leaking.

In extremely severe circumstances, your oil may just vanish, and you will need to replace it every day. You should regularly check the oil level because of this.

Consider that you are merely unaware that the rear main seal has failed. You make a thousand kilometers of driving without paying attention. The engine abruptly shuts down and refuses to start.

Your engine is now finished, thus this means. In this situation, you will require a brand-new replacement engine, which would set you back thousands of dollars.

The VTi transmission by EMcCutchan Any kind of misalignment that may occur in both automatic and manual transmission vehicles, be it of the input shaft of the gearbox or the flexplate might put stress on the rear main seal leading to a leak.

Make sure your oil level is in control if you are having spills on the ground. By checking the oil level periodically, you’ll be aware of any oil loss and be able to top off your engine’s oil supply before it runs out, preventing severe engine damage.

4. There Is a Burning Oil Scent In the Vehicle’s Hood or Cabin

Leaking oil will adhere to engine components and burn at high operating temperatures, especially when it drips in very little volume. Lifting the hood will reveal a strong smell of burning oil, which is rarely detectable within the cabin but will alert you to an issue.

What are the Causes of the Rear Main Seal Leak In a Car?

The rear main seal might leak for a variety of reasons. Let’s briefly examine the causes of rear crankshaft seal deformation or deterioration.

1. The Usage of Incorrect Lubricant Oils

The engine may leak if the incorrect sort of oil is used. The seals may be impacted by the chemical additions in today’s engine oils.

If you use an oil that isn’t meant for your engine, the seals might easily degrade. In addition, the oils may cause the seal to dry up and stiffen with time, opening the door for a leak. Use just the recommended oil per your owner’s handbook.

It could also be brought on by an engine with too much oil.

2. Incorrect Installation of the Rear Main Seal

A polytetrafluoroethylene covering is present on the back seal. It must be installed dry to form a tight seal. Additionally, it is made to seal better than silicone or Viton and to stop wear.

You’re asking for trouble if you oil the seal during installation. After installation, it can start leaking.

3. A Faulty Main Bearing

The crankshaft begins to hang within the engine when the main bearing fails, which causes the seal to stretch while the engine is running. The seal will inevitably leak because it wasn’t designed to be pushed and stretched.

However, you will receive reasonable notice that the main bearing has failed. This failure ought to make a ton of noise, and there’s no need to keep driving your car while it’s still broken.

4. Damaged or Broken Crankshaft

Around the crankshaft itself is the rear crankshaft seal. The crankshaft’s surface cannot seal completely if it is damaged or otherwise flawed.

For a consistent fit, the surfaces must be similar. The crankshaft surface has to be fixed if it doesn’t fit completely.

5. An Obstructed/Clogged PCV System

The shaft is supported by the rear crankshaft seal. The seal may leak if the crankcase is being compressed beyond its safe operating range.

This elevated pressure might be brought on by a blocked positive crankcase ventilation system. It will exert pressure on the seal and cause a leak if left uncontrolled.

Crankshaft with flying arms by Crankshaft_jap.jpg / CC BY 2.0 Silicone or rubber is used to make the rear crankshaft seal. The crankshaft rotational forces, corrosion from road salt, and other environmental variables cause the seal to deteriorate over time.

6. Misalignment of Transmission Components

No matter the kind of transmission in your automobile, misalignment may occur in both automatic and manual vehicles. Any misalignment of the input shaft of the gearbox or the flexplate might put stress on the seal.

This flaw can be found by quickly inspecting the flexplate on the automatic gearbox. If you have a manual transmission, you should instead check the input shaft.

How Much Does a New Rear Main Seal Cost?

Replacement of the rear main seal typically costs between $700 and $1000. The cost of labor is expected to be between $500 and $800, and the cost of parts is between $35 and $50.

Taxes and other costs are not included in the estimate. Depending on the make and model of your car and the store where you buy spare parts, this price may change. Replacement of the rear main seal is estimated to cost between $1000 and $2500.

According to rumors, labor takes eight hours to complete, which affects the whole cost. As a result, the cost of labor is substantially more than the total cost of the parts. Due to the following variables, the complete procedure is typically quite expensive:

What Determines the Cost for Replacing the Rear Main Seal?

First, you should be aware that the price to replace the rear main seal will vary based on the year, make, and model of the vehicle, as well as the mileage, present condition, and oil levels.

You might be asking why replacing the rear main seal on a car costs hundreds of dollars while the seal itself can be replaced for less than $50.

The majority of the fee that you will be paying at an auto body shop is because replacing the seal, and maybe the gaskets, seals, and other components, requires a significant amount of effort.

1. Labor Charges

Unfortunately, labor expenses will need to be incurred to fix your car. It doesn’t take many hours or is a tough task to replace a rear main seal.

The procedure of separating the transmission from the motor necessitates the removal of the motor, and the technician must take care of the accessories, cables, and housing that need to be avoided or tagged, which raises the cost of replacing the rear main seal.

The expense of replacing the rear main seal is increased by the need for costly equipment to remove parts this big within your car.

2. Cost of Additional Parts to be Replaced

Other parts of your car might need to be replaced when you repair the rear main seal. For instance, it was typically necessary to remove the oil pan. A new gasket must be installed by the mechanic after removing the oil pan.

Oil leaks are most often caused by a damaged gasket. In addition, because your technician is already there and has already done the labor-intensive task, you can decide to repair the clutch or the front crank seal, saving you future labor expenditures.

3. Harm to Additional Parts Because of Excess Leaks

Additionally, if there is an oil leak, there is always a pool of liquid below your automobile, which might harm the sensors and cables within your car. Make careful to assess if the expense of replacing the rear main seal is worthwhile for you.

Dual-mass flywheel by Cschirp / CC BY-SA 3.0. The mechanic must first remove the transmission and the flywheel/flexplate to get access to the seal housing after he is certain that the rear main seal is the source of the leaks.

Why Is Repairing the Rear Main Seal So Expensive?

We occasionally overlook or take for granted the abilities needed to be a good mechanic. Even though the powertrain is incredibly resilient, it can only be repaired with care because it is not a simple piece of metal. Also, consider the cost of the specialist tools the technician will need to purchase to operate on the rear main seal.

Your mechanic shouldn’t and most likely won’t accept your diagnosis, preferring to personally investigate the issue. He must first remove the transmission and the flywheel/flexplate to get access to the seal housing after he is certain that the rear main seal is the source of the leaks.

Hours are spent on the procedure, and each component must be meticulously cleaned and treated with care. Everything needs to be put back in its place once the rear main seal has been replaced before more testing can verify whether the repair was successful.

Is the Expense of Replacing the Rear Main Seal Worthwhile for You to Incur?

You can only decide if you want to spend this much money on your car once you get an estimate of the cost of replacing the rear main seal. Is your automobile in excellent condition and is the cost justified?

Driving while experiencing a rear main seal leak is risky since it quickly causes the oil level to drop. Your engine may suffer serious damage from low oil levels, necessitating future replacement and maintenance that will be more expensive.

What Happens During the Replacement of the Rear Main Seal?

The technician will need to add a dye to the oil to identify the source of the oil leak in your automobile. The rear main seal leak can be located by looking at the oil under a UV light.

Once the problem has been identified, the mechanic may pinpoint the leak’s source and calculate the price of replacing the rear main seal.

To effectively reach the rear main seal and the leak, the mechanic must still remove the gearbox and flywheel. Transmission fluid leaks may occur if the seals have deteriorated.

After removing the housing for the seal, the surfaces on the sides will be cleaned and maintained to eliminate any sludge and dirt. The replacement of the gearbox and other internal components of the engine follows the installation of the new seal.

Is It Possible to Replace a Rear Main Seal Without Removing the Transmission?

A vehicle’s transmission must be taken out to replace a rear main seal conventionally. This is required to obtain access to the actual rear main seal, which is situated inside the bell housing of the gearbox at the rear of an engine.

Unfortunately, removing a car’s transmission is a difficult task that takes some time to execute.

Fortunately, many devices on the market now promise to halt rear main seal leaks in their tracks. These goods are made to hydrate an old seal again, regaining its sealing ability. Unfortunately, people tend to avoid these items since they are known to have inconsistent outcomes.

A rear-hinged clamshell hood by Ballista / CC BY-SA 3.0 Lifting the hood will reveal a strong smell of burning oil, which is rarely detectable within the cabin but will alert you to an issue that’s associated with leaking oil. One of the culprits can be the rear main seal leak.

The enormous favorable feedback that a select few of these stop-leak solutions have gotten, however, makes them stand out above the competition. Customers frequently mention BlueDevil Rear Main Sealer as being a “cure-all” for rear main seal leakage as an example of such a product.

In any case, customers who give a rear main seal stop leak product a try have little to lose. After all, using a single-application sealant is a welcome alternative when the only other option is prolonged vehicle downtime and high repair expenses.

How Serious is the Rear Main Seal Leak?

Because such leaks only frequently get worse with time, a rear main seal leak is typically thought to be highly significant.

A rear main seal leak can occasionally become so serious that it becomes impossible to maintain the oil loss that results. Simply put, it becomes difficult to add enough oil to keep a sufficient supply of lubricant.

Even yet, this situation is still far preferable to what would most certainly happen if a rear main seal leak causes an engine to run out of oil. Any significant loss of lubricating oil carries the danger of damaging the bearings, which might eventually lead to an unexpected engine failure.

Running an engine with insufficient oil can and will, at the very least, result in early internal wear. In any case, a rear main seal leak has to be fixed as soon as possible.

Even while fixing a leak of this kind can be complicated, it is still far less onerous than having to replace an engine after it has suffered from persistent oil loss for an extended period. Make an appointment with a reputable service shop as soon as possible if you are not capable of doing such repairs yourself (the majority won’t be).

What are the Benefits of Replacing a Defective Rear Main Seal?

To reduce the expense of repairs on other components of your car, you must replace your rear main seal for a variety of reasons.

Even if it isn’t urgent, the sooner you replace the rear main seal, the sooner you will have a well-functioning car that won’t create any further issues.

You will be able to prevent overuse from wearing down your engine, gears, and other components. If the leak is not fixed, the components, such as the camshaft, will begin to wear down too soon.

Additionally, you will safeguard your car against oil leaks, which can harm and corrode internal components. The expense of replacing the rear main seal is more and is more important to preserving the longevity of your car since oil leaks might worsen engine problems.

And last, you won’t need to pay close attention to your oil levels. You won’t be wondering when to top up your automobile while driving if you extend the life of the rear main seal and have it changed.

How Do You Replace the Rear Main Seal?

Your car might suffer severe damage from a rear main seal leak. You must act quickly to stop the leak if you notice that you are losing oil there before it can seriously harm your engine.

If the seal has shrunk, has somewhat deteriorated, or has warped as a result of irregular oil changes, you don’t need to spend a lot of time on it. If this is the case, the seal merely has to be reconditioned rather than replaced.

A BMW engine by Kether83 / CC BY 2.5 The rear main seal is located in the back of the car engine. Despite being located at the back of the engine, the seal is not always there. Different engines have various faces.

It is common knowledge that engine seals degrade over time as a result of heat, oil acidity, and some other related factors, typically as a result of poor maintenance. The rear main seal stop leak is required in this situation to recondition the seal and make it functional for a few thousand kilometers.

Get a blue devil rear main sealer to recondition the rear main seal. The purpose of this device is to halt the rear main seal leak. It accomplishes this by repairing rubber gaskets and seals, and it is safe to use on both gas and diesel engines. It is also a great fix for timing cover leaks.

Additionally, it works with both synthetic and regular oils. Remember that if the seal has a chunk missing, a tear in it, or a hole in it, this won’t work. A large hole or chunk on a rubber seal cannot be fixed by any product. So, if the rear crankshaft seal has a huge hole in it, patch it by following the instructions below.

1. Remove the Battery

You must unplug the battery after using a floor jack to lift your automobile. The starter needs to be removed before you can remove the transmission.

Make sure the starter has not sustained any damage. The typical price to replace a starter is between $430 and $700. You should cut the negative connection from the battery to prevent short-circuiting and any other electrical issues.

2. Take Out the Exhaust System

You must tip the engine at a downward angle to make adequate space for the removal of the transmission, which may be done securely. The exhaust system may also need to be partially removed or perhaps fully removed if it is blocking the transmission.

3. Take Out the Driveshaft

Regardless of whether your vehicle has front- or rear-wheel drive, you will need to remove the driveshaft or CV axle to make way for the transmission.

The automatic or stick shift will need to be taken out for the clearance, which calls for you to take out the driveshaft bolts, flange, and inspect the U joints, then put the driveshaft back in and put the bolts back in.

4. Take Out the Transmission

The transmission has to be removed next. Regardless of whether the transmission is an automatic or manual shift, it must be removed. Check to see whether the transmission requires any maintenance, such as a fluid clean or solenoid replacement.

The automatic will have two cooler lines coming up through the radiator, which is the primary distinction between these two. The torque converter must be detached from the flex plate by undoing these two lines with a tool.

Using the 3/8-inch drive socket and ratchet, remove each torque converter bolt one at a time. Turn the crankshaft in the usual direction after removing a bolt. When the subsequent bolt comes, you can repeat this method till then.

5. Uninstall the Flexplate or Flywheel

You will have a clutch and flywheel if your automobile has a conventional gearbox. Before changing the rear main seal, these two components must be taken out of the car. The flexplate must be taken off of an automatic gearbox vehicle. Congratulations, unbolting this mechanism is now simpler.

Crankshaft with four main bearings by Dana60Cummins / CC BY-SA 3.0. The anatomy of the crankshaft is a cylindrical metal component that is situated in the center of the rear main seal.

6. Take Off the Bolts of the Rear Main Seal

You are now getting to the rear main seal after making space for the transmission and removing the extraneous components.

The crankshaft is a cylindrical metal element that is located in the middle of the rear main seal, which is its anatomy. Only rear-wheel-drive manual automobiles have a pilot bearing, the smaller component in the center of the crankshaft.

To reach the rear main seal housing, remove the engine plate using a big screwdriver. Now, you could discover oil pan bolts passing through the oil pan and into the housing of the rear main seal. Take these bolts out.

Bolts will be used to secure the seal housing to the back of the engine block. Turn these bolts in the opposite direction to remove them. You may now remove the seal housing in its entirety. To remove the housing from the engine block, pry it off with a big screwdriver.

7. Uninstall the Crankshaft Seal of the Rear Main Seal

The primary crankshaft seal at the back can sometimes become trapped. You must employ a delicate prying method to get rid of the seal. Now, manually remove the hub’s rear main seal.

8. Fit Your Replacement Rear Crankshaft Seal

If you intend to replace the old rear main seal with a new one, you must ensure that the new option and the old unit are internally compatible.

9. Set Up the Replacement Seal

To remove the old gasket material from the seal housing, use a gasket scraper. You may put the seal in the housing once the area has been cleaned. Hammer the seal into place evenly. Apply a thin coating of sealant once the seal has been fitted.

10. Replace the Rear Main Seal

Before changing the seal, smear a little engine oil over the crankshaft hub. Reposition the block and oil pan bolts, then tighten them after pushing the seal housing into position. To complete, tighten the oil pan bolts. Install the retainer by using a tiny punch and a hammer.

Replace the rear main seal yourself to save money if you are strapped for cash and don’t want to pay a technician to do the job.

The Conclusion

There is no getting around the reality that repairs for a rear main seal leak will be quite expensive. Even more annoying is the fact that the majority of rear main seals can be purchased for not too much money. However, the labor expenses for such repairs are frequently high.

These personnel expenditures are, of course, easily justifiable. It’s not simple to replace the rear main seal on an engine, and it takes a lot of time.

This type of repair necessitates the removal of the vehicle’s gearbox since there is no other way to get access to the engine’s rear main seal. In the case of four-wheel-drive cars, the transfer case must frequently be removed as well.

The precise cost of replacing the rear main seal varies from vehicle to vehicle and is determined by the manufacturer’s stated flag time for such repairs. The drive layout of a certain vehicle affects the cost of replacing the rear main seal.