Rear main seal leak

Rear main seal leak – Sign, symptoms, and repair

A rear main seal leak is one of the common engine problems. It refers to a leak from the main seal on the back of your engine. This seal is under pressure any time the crankshaft is in motion and does what it does best keep oil in the crankcase and not on the ground.

The rear main seal on your vehicle is its most important seal, it protects the crankshaft and internal engine components from oil leaks.

It is important to know that the rear main seal leak is quite common and can be fixed. There are many things you can easily try by yourself. If those steps do not work, then it is time for some professional help. It does not have to be costly and you will be able to enjoy your ride as well as save some money at the same time.

What is the real main seal and its importance?

Rear main seal leak

A rear main seal is a seal located in the engine block of various automobile engines. It prevents oil from escaping the crankcase and is thus part of the larger rear crankcase assembly. The name “rear main seal” is because this component seals the main bearings on the crankshaft in the rear of the timing drive belt or chain. Also, there is a front main seal that seals the main bearings in front of that timing drive belt or chain.

If the rear main seal ever gets damaged, your vehicle is likely to begin leaking lubricating oil. Since this seal is what keeps oil inside of the engine when it’s running, a leak could spell months if not years of expensive engine repairs.

Therefore, you must give all attention to your car once you notice any leaking beneath the car. Once you notice it is the real main seal, you should get the car to the mechanic to get it replaced or fixed.

Types of rear main seal

The rear main seal is an integral part of the torque converter that is required for a smooth drive. There are many types of rear main seal leak, even though it is located inside your vehicle.

  • Rope or Wick Seal

The rope seal is designed to be used on the inner tube and is fitted in from the center of the unit. The rope/wick seal is placed over the inside tube, with the bottom of the seal in contact with a flat surface. The purpose of this seal is to seal any leaks occurring at the bottom of the inner tube.

Rope seals are more effective than wicks when it comes to oil leaking around the crankshaft. Most and not all rope seal is designed to withstand up to 500-degree F temperatures (200 times more than traditional rope seals) and is more effective at sealing than traditional rope seals.

  • Split seal

A split seal is a type of rear main seal used on many trucks and SUVs. It is made up of 2 separate seals that are joined by a vent tube, with the vent tube extending to an opening in the side of the block.

The split type of rear main seal is something that most automotive enthusiasts are very familiar with. It’s a design that dates back to the early version of the Model T Ford and is still in use to this day. The way it functions is by splitting apart during the installation process, which makes it easier when you’re trying to get everything seated properly.

  • One-piece seal

The one-piece rear main seals go inside the engine block and have a one-piece rubber seal that wraps around the perimeter of the block to prevent oil leakage.

The one-piece seal is the most basic and traditional rear main seal. No part of it is ever replaced, buying a replacement gasket would be unnecessary and wasteful. Even with the best seals on the market, there will always be a slight chance of oil leakage.

Rear main seal replacement cost

When the rear main seal on your vehicle becomes worn or damaged, it can cause oil leaks. If you notice an oil leak coming from under the drivetrain of your vehicle, then you probably have a rear main seal leak and will need to replace it. Several different vehicles have rear main seal leaks, so make sure you identify yours correctly before ordering this part.

Also, a rear main seal leak can increase your expenses, because not only will you have lower fuel economy, but you will also be burning more oil past the piston rings and into your crankcase.

Replacing the rear main seal can be an expensive endeavor as the replacement part can cost between $400 to $2500 depending on the car brand and model. You can always get quality parts from reliable auto stores near you or online.

Rear main seal leak repair cost

The rear main seal leak repair can be difficult to do on your own, but fixing it yourself is cheaper than the dealer would charge you. The most important thing to consider when you’re attempting a rear main seal leak is finding the cause.

Rear Main Seal leak repair cost is usually $705.00 to $1,065.00 and sometimes the repair cost depends on the age and makes of your car. The rear main seal is easy to replace and a replacement can take as little as one hour. Once you get it done rightly, the leak will stop when you fix it.

Rear main seal leak symptoms

If your vehicle has a rear main seal leak, you may notice a few different symptoms. You may see puddles of oil under the car. You may also notice an oil stain on your driveway. The check engine light may be flashing, or your engine may make clunking sounds under acceleration.

In addition, it can make hydraulic gurgling sounds and you may smell burning rubber.

Rear main seal leak causes

To ensure your car works optimally once you notice leakage of oil, the first thing is to know What causes a rear main seal to leak? The rear main seal is designed to prevent engine oil from leaking out of the crankcase. Over time, seals can become worn due to the normal wear and tear of components moving against them.

When this happens, oil can leak into the transmission fluid, causing fluid contamination and abnormal wear. Searching for this cause will take quite a bit of time, but it is worth it because if left un-repaired and undetected oil will continue to leak out of your rear main seal daily and burn up the transmission prematurely.

  • Worn main bearings

Rear main seal leak can be caused by worn main bearings. The rear Main seal prevents oil from leaking out of the timing chain cover while preventing contamination of the crankcase. Therefore, replacing a leaking rear main seal can prevent further damage to the crankshaft, connecting rods, pistons, and other engine components.

  • Clogged or blocked PCV system

A clogged or blocked PCV system is one of the most common causes of a rear main seal leak. PCV stands for positive crankcase ventilation and it is an emission control device in a vehicle. Its system uses a vacuum to force oil vapors back into the engine s crankcase and then vent them through the PCV valve, back into the engine s intake manifold.

When a vehicle’s PCV (positive crankcase ventilation) system or rear main seal becomes clogged or blocked, pressure from the crankcase cannot escape, and oil is forced back into the engine. This can cause several different types of problems in your vehicle.

If a rear main seal leak occurs as a result of a clogged or blocked PCV system, then the rear main seal itself may need to be replaced. Leaks in the engine can allow oil to escape through the gasket on the crankshaft or where the flywheel housing mates with the engine block, causing wear and possibly even damage to other engine components.

  • Crankshaft condition

The rear main seal protects the crankshaft in the engine. It prevents oil leaks. The leak may be caused by a damaged crankshaft, which is produced by improper machining of the crank snout, a worn or broken thrust washer, or damage from internal combustion gasses that have entered the crankcase.

Also, the crankshaft seals the main bearing assembly and allows oil to circulate in the rear main area. The crankshaft seals have been known to leak at the front main bearing due to thrust washers wearing out which can cause excessive oil leaking out of the rear main seal.

  • Seal coating

The engine seal coating consists of a very thin layer of hard plastic called polytetrafluoroethylene or PTFE that acts as a lubricant, preventing parts in the engine from rubbing together and causing excessive heat.

A rear main seal leak indicates that the seal coating on the rear main crankshaft has worn away. This is caused by engine oil entering the water jacket as a result of an insufficient crush on the crankshaft.

Is driving with a rear main seal leak safe?

The rear main seal is a critical part of your engine. If it fails or leaks, you will have serious damage inside your engine in a short time. Unfortunately, some people just ignore the leak hoping they can make it to their destination without a problem.

Sometimes they are lucky and nothing happens. But if the seal leak runs long enough and gets worse, there is no doubt that it can cause significant engine damage. If you are driving around with a Rear Main Seal leak, then a major catastrophe will happen eventually.

Is a rear main seal leak serious?

Yes, a rear main seal leak is serious. A rear main seal leak means that the crankshaft seal in your car engine has failed and is leaking oil out of the crankshaft into your transmission. Without the crankshaft seal, your car will be losing a lot of oil out of the crankshaft which will ultimately cause severe internal engine damage.

Leaking oil from the rear main seal can be an expensive disaster if allowed to continue. So, you must find a lasting solution once you experience leaking which is to fix or get a replacement.

How much does it cost to fix a rear main seal leak?

A rear main seal leak can affect any car and when the leak is not treated. The problem can grow much larger and cause more damages. The typical cost for a rear main seal leak repair is about $1300–$1700 range.

Please take note that the price range for the repair of the rear main seal all depends on several factors. Some of them are the experience of the mechanic, the tools, location, car age, brand and model, and many more.

Is it worth fixing a rear main seal?

This varies from vehicle to vehicle, but yes, it is worth fixing a rear main seal. The engine seals keep the oil inside the engine and prevent oil from leaking out of the engine. Also, it prevents moisture from entering the system. If an engine does not have a seal or if that seal fails, the oil will leak out onto the ground.

Your vehicle must be level when you check this so you can notice if there is any seepage when you check it. If there is, then it’s time to change your rear main seal and replace this vital part of your engine.

However, if you find it hard to do it all by yourself, you should get your car to the mechanic. The mechanic is well experienced and they know the things to do with fixing the engine and ensuring it gets to work optimally again.

How do I stop my rear main seal from leaking?

The use of a sealer is an economical way to stop the real main seal from leaking. To stop a rear main seal from leaking it is important to follow the steps below. First, you need to determine where the leak is coming from, it will most likely be coming from either the flat pan or gasket that fits between the transmission and engine block.

After you have determined which component is leaking behind the rear main seal you need to clean any debris off of it and apply a thick bead of sealer right around the edge of the component that is leaking.

You should get the right sealer from any local store or online store. The Bar’s Leaks Concentrated Rear Main Seal Repair will work perfectly and it thus helps to ensure the leaking stops for most real main seals.

How long can you drive with a rear main seal leak?

The average person can drive about 300 miles before a rear main seal leak makes it essential to pull over, exit the vehicle, and add oil. The seal, located behind the transmission gearbox in most vehicles, is backed by two babbitted surfaces that help reduce vibration. Most often a rear main seal leak appears when one of these surfaces wears out and begins to leak.


The rear main seal leak is one of the major vehicle problems that happen when the rear main seal of the engine fails. The rear seal is located at the bottom of the engine near the transmission. Its main role is to keep oil in the crankcase and flow to the crankshaft, camshaft, and other oil-flush components of the engine when the vehicle is running.