Jan. 05, 2024
Do you have oil spots in your driveway, or a leaky engine block when you look under your vehicle? Sorry, super bad news: you might have a rear main seal leak. Few words from the mechanic will stop every driver in their tracks quicker than “You have a rear main seal leak!”
A rear main seal leak is among the worst things that can happen to any vehicle because the rear main seal is very hard to reach and it requires much of your engine to be disassembled.
On most modern engines, the seal’s failure is due to a condition inside the engine or a component connected to the back of the engine and is most common in older cars.
For many drivers, news of such a problem means that it could be time to purchase a new vehicle because rear main seal repair typically costs more than the value of vehicles old enough to develop such leaks.
Replacing a rear main seal is one of the most dreaded, labor-intensive, and expensive jobs you can do on your car next to replacing the head gaskets or rebuilding your transmission. It can easily cost you from $800 to $1,200 at a mechanic.
In addition, there are no shortcuts or quick fixes if the seal has expired. A replacement isn’t something you’re going to want to take on yourself and even a seasoned mechanic can struggle with it as it’s in a painfully difficult position.
That said, a correct diagnostic will save you a lot of money by having a mechanic check whether your current oil leak situation is indeed a rear main seal leak. In addition, in certain mild cases, you can spend less than $20 to fix the problem.
Read on to learn everything you need to know about rear main seal leak, including how the rear main seal works, rear main seal leak symptoms, and causes, how to troubleshoot, and what to do.
The rear main seal is designed to prevent oil leaks between the block and the crankshaft. Manufacturers originally intended rear seals to last the life of a vehicle so that no replacement is needed, unlike many other engine components under the hood that require replacement every few years.
It is situated just outside of your rear main bearing, which supports the crankshaft for your motor in your engine. These bearings carry the majority of the load in your engine and play a crucial role in turning the axial motion of your piston into the rotary motion of the crankshaft.
The main bearings do this by absorbing the axial load of the piston being forced down by combustion, all the while still allowing the crankshaft to spin.
To accomplish this task, these bearings have to be incredibly smooth and stay well lubricated by the oil in your engine. In other words, the correct oil for your engine is extremely important in creating the optimal condition for the main bearings to do their job without excessive wear and tear.
This oil also has to be contained within your engine to continuously keep everything lubricated, and this is exactly where the rear main seal comes in. The rear main seal allows the crankshaft to exit the engine case so it can bolt to the flywheel or flex plate and transfer its energy into the transmission.
The rear main seal also holds the engine oil back and keeps it inside your engine where it can keep your main bearings lubricated.
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The average cost to repair a leaky rear main seal is anywhere from $800 – 1,200 dollars. In rare cases, some drivers have reported getting quotes of up to 2,500 dollars on certain vehicles.
Driving with a rear main seal leak is dangerous due to the high possibility of a very fast leak. A fast leak will lower your engine oil level to dangerous levels very quickly, which can lead to permanent engine damage.
The possibility of a fast leak is very likely, as the rear main seal is in a place that gets a lot of oil thrown at it and has the added wear of the crankshaft spinning inside.
If the seal tears or cracks even only slightly, the crankshaft rotation can cause the seal to get torn up very quickly causing a fast leak.
A quick side note is that when a vehicle is parked at an angle, an oil leak is bound to escalate much faster. Therefore, if your driveway is built on an incline, park your car on the level street in front of your house until the problem is fixed.
On vehicles with a manual transmission, the clutch disc can become soaked with oil if you let a leak persist for too long.
Some seals and gaskets in your engine never cause severe leaks because of the design or because they are not subjected to high oil pressure in the engine.
In contrast, the rear main seal is an engine component that is highly likely to develop a leak. This is because it is subject to high oil pressure since it is right by the rear main bearing as well as the spinning crankshaft, which is constantly wearing on the inside of the seal.
No matter how often you change your oil, eventually, the spinning metal crankshaft will wear down the seal enough to cause a leak.
As mentioned before, rear main seal inspection and replacement require much of your engine to be disassembled. Therefore, labor costs would be very expensive and of course, if you are not a professional handyman, this would be a very complicated project.
The problem is the location of the rear main seal. It is at the back of the engine and seals the crankshaft as it exits the engine. Your vehicle’s flywheel or flexplate is then bolted onto the crankshaft flange sandwiching your rear main seal between your engine and transmission.
To replace the seal, either the engine or transmission will have to be removed. Once one of those is removed, the oil pan also has to come out too, so this maintenance job is extremely labor intensive.
The majority of older vehicle models use the rope or wick seal, with a small number using the split seals. Meanwhile, newer models use the one-piece seal for improved performance.
Rope seals and split seals are much more universal and can work on almost any engine, while one-piece seals are less prone to leaks.
Named because of its resemblance to rope and lamp wicks, this seal is designed to handle the impacts of intense crankshaft rotations and the friction caused by fluctuations in temperature.
Consequently, a rope/wick seal can fail in two ways: shrinking in cold weather or expanding in hot weather. The seal is lubricated to avoid drying out with a small amount of oil, which also keeps it fitted in its place next to the crankshaft.
In modern cars, the new design of rope seals lacks the strength of the older version when it comes to preventing stray oil.
According to many professionals and specialists, such a change in design is due to stricter environmental regulations, which have restricted the use of materials like asbestos.
Such regulations forced manufacturers to cut corners to lower the cost of producing the rear main seal. As a result, most modern day rope/wick seals are vulnerable to crankshaft contact and engine speed and therefore need to match the RPM requirements of your engine.
To avoid bad replacement rope/wick seals, only buy from reputable parts suppliers, and best to check reviews on Amazon before making a purchase.
Made of rubbery material, the split seal has a lip shape and is fitted in one direction to prevent the passage of oil. Though effective for this purpose, neoprene seals are equally vulnerable to leaks as rope/wick seals.
One-piece seals are the hardest seals to service and lack the universality of rope and split seals. With its unique round design, the one–piece seal only works on specially-made crankshafts.
Therefore, you cannot install one–piece seals in older engines without a crankshaft replacement.
The issue can be hard to identify because the parts in question are relatively unknown to most car owners. The hard-to-reach location of the rear main seal goes to show how this part of the vehicle was never really intended to be replaced during the span of the car’s ownership.
How to tell if rear main seal is leaking? The main symptom of a rear main seal leak is when your car starts leaving black stains on your driveway or parking lot.
Another sign is aggressive oil loss: you find yourself needing to top off your oil more frequently, despite the same routes and driving conditions. At the early stage of a leak, oil loss might not be rapid enough that you would find black stains where the vehicle has parked.
While you might see an oil stain in your driveway overnight, the leak might not be fast enough to leave its mark in the supermarket parking lot on your grocery trip. Therefore, you might need to run tests to determine whether you’re losing oil or not.
>> READ MORE: How To Replace A Rear Main Seal Without Removing The Transmission
There are many rear main seal leak causes. Any of the following conditions can cause your rear main seal to leak because they can deform or deteriorate the seal.
If your vehicle has worn main bearings, the crankshaft is able to move excessively inside the bearings which will stretch and move the rear main seal while the engine is running. This will allow oil to leak past the seal.
It is difficult to tell if your engine has worn main bearings without removing a lot of components.
If this is the cause, you’re most likely in for a full engine rebuild which would include removing the motor and replacing many other components in addition to the rear main seal itself.
Most rear main seals have a lip that rides on the shaft. The pressure inside the crankcase will push the lip onto the shaft. Too much pressure will eventually cause the lip to balloon and allow oil to pass.
Then when will there be too much pressure? If the Positive Crankcase Ventilation (PCV) system is blocked, it will increase the pressures inside the crankshaft and push out the seal.
Otherwise, if the engine is supercharged or turbocharged, excessive blowby due to worn or damaged piston rings can cause increased crankcase pressure that can also damage the rear main seal, causing a leak.
Another common cause could be a low oil level or using the wrong type of oil. Most oils have chemicals in their additive packages that will condition the seals in the engine. If the oil is not changed regularly, it will cause the seal to deteriorate.
The seal conditions are depleted over time along with buffers in the oil. The lip that rides on the crankshaft will become stiff and will not be able to seal itself against the crankshaft.
The rear main seals have a lip that directly rides on the crankshaft. Therefore, the condition of the surfaces that the rear main seal rides on is critical. Any imperfections or wear on the crankshaft can cause a leak. There are sleeve kits that can be installed on the crankshaft to restore the surface.
If there are any alignment problems with the bell housing or input shaft of the transmission, they can cause stress on the rear main seal. Make sure you check the input shaft on a manual transmission. On vehicles with automatic transmissions, check the flex plate for lateral runout or damage.
In rarer cases, some rear main seals need to be installed dry. These seals have a polytetrafluoroethylene (PTFE) coating on the lip seal that needs to be dry and seat to a dry surface on the crankshaft.
The seal will transfer a layer of PTFE to the crankshaft surfaces that the lip will ride on. The transfer layer prevents wear while sealing better than a silicone or Viton material. If the seal is installed with a coating of oil, it will start to leak in a few miles.
Since the rear main seal is in a position that you won’t be able to slide under your car and inspect directly, your best course of action upon finding stains in your garage is to go through a process of elimination.
If you seem to be losing oil but you don’t have a noticeable drip when the car is parked you may be in the early stages of a leak.
The first step and a simple way to test if your car is leaking oil is to idle the engine for 15 minutes to see whether any oil appears on the surface underneath. Since the car’s movement and other car parts can tend to hide oil leak symptoms, most evidence of leaks is overlooked.
For example, oil could be getting splashed along chassis components as you drive at highway speeds. By running the car at a standstill, you get a better indicator of how oil is consumed during commutes along roads and highways.
In the case that you’re finding oil stains or experiencing excessive oil loss, it is not necessarily your rear main seal that is leaking.
On most engines, oil leaks can occur above and below the rear main seal. It could be a leaking oil pressure sensor, oil pan gasket or galley plug near the seal that causes oil to come from the bell housing. Adding dye to the oil can help reveal where the oil is actually coming from.
If you have determined that your car is leaking oil, check the transmission and oil pan. If oil appears on the front of the transmission and at the back of the oil pan, it could be due to a rear main seal leak, but there are still other possibilities.
Therefore, it’s important to check further up in the engine compartment for drips. After all, you might discover a critical yet different problem with your vehicle that would ultimately be easier and cheaper to fix.
Other places to inspect for leaks are the valve cover gasket and valley pan. The cover gasket and valley pan are easier and less expensive to replace than the rear main seal.
You’ll need to get under the vehicle with a flashlight to check these parts. For added protection, you’ll probably want to put on grubbies, goggles, and protective gear around your head.
You are extremely lucky if your seals have simply shrunk or are slightly deformed due to a lack of frequent oil changes and thus only need to be reconditioned without having to be replaced.
Very often, engine seals become dry and crack, due to heat, oil acidity, and a host of other maintenance-related results, usually from a lack of maintenance.
In this case, very often simply reconditioning them can bring them back to life for a short period, and they will perform just fine for tens of thousands more miles.
However, of course, you cannot expect to drive a car 500,000 miles and expect the rear main seal to never fail again.
To recondition your rear main seal, look for an oil-stop leak product. These oil-stop leak products can recondition the seals, or at least in some cases prolong the leakage and slow it down long enough for you to either keep driving it the way it is for a while or buy you some time until you can save up enough money to get it fixed by a local mechanic.
Do note that these will not work if your rear main seal has a hole, tear, or a chunk missing out of the gasket seal itself. No product will be able to replace the giant hole in the rubber seal material itself without taking the car apart.
There are a few specific ones from three reputable companies, including BlueDevil Rear Main Sealer ($15/8oz), AT-205 Seal Leak Stopper ($10/8oz), and Bar’s Leaks 1040 Grey Concentrated Rear Main Seal Repair ($5/17oz).
If you notice your car is losing or burning oil at a faster-than-normal rate, but you don’t see oil puddles on the ground; and you’ve noticed billowing exhaust from your tailpipe each time you start the engine, the issue probably isn’t due to a rear main seal leak. Instead, this can be caused by a valve seal leak, a pretty common problem.
Common causes of seal valve leaks include vehicle age and mileage. However, the most likely reason for a seal leak is the prolonged storage of a vehicle.
When you store a vehicle in a garage for weeks or months on end, the seal can dry and harden, which can ultimately lead to cracks and leaks.
How to check for engine oil leak
Looking under the engine hood of a vehicle is usually done at service centers or by mechanics. But an oil patch either under the hood or the vehicle is hard to ignore. Often engine oil leaks are a warning sign from the engine that something is amiss. It’s always advisable to get professional help to look into an engine oil leak but in the meantime, here are a few ideas why your vehicle could be leaking oil and where are the common places to look for one.
Fact:
The main cause of leaks in engines of older vehicles is the excess build up of sludge leading to damaged gasket valves. Sludge buildup can lead to increased engine pressure and cause leaks. A good quality oil helps avoid sludge and keep your engine healthy. #MythvsFact pic.twitter.com/34tUJOboBX— Divyol by Gandhar Oil (@Divyol) October 28, 2020
Common reasons why a vehicle could be leaking oil
The most common reasons for an Engine oil leak are the result of a broken seal or busted gasket. It could also be due to worn-out parts or hoses. If you find your vehicle leaking oil, the source may be one or more of the following:
Signs of an engine oil leak
A few basic signs of an engine oil leak could be as follow;
Consequences of an engine oil leak
An engine oil leak could lead to many problems in your vehicle, some of those could be irreparable damage not just to the components of your engine but also to the multiple parts of the vehicle that the engine connects to such as rubber hoses and seals used in these components and cause them to wear down earlier than expected. Engine oil leaks are a fire and a major safety hazard to you and the environment.
Well, this is embarrassing. You’ve just pulled out of the driveway after having parked your vehicle for a while, and there it is–a puddle of brown, greasy-looking liquid. In some cases, it may be pretty easy to identify when your car is leaking oil when parked, but quite difficult to know for sure what the cause is. Oil leaks aren’t just unsightly, they could indicate some major issues within the engine. So, what causes a car to start leaking oil and how can it be fixed?
In the past, the most obvious sign of an oil leak was evidenced by a brown, greasy spot found in your garage, parking spot, or driveway. Today, though, many modern vehicles have protective shielding that often catches the oil long before it hits the ground. That may be good for your driveway, but not so good for you when trying to identify a possible major leak. Low levels of oil are most certainly a sign of leakage. For that reason, it is recommended you check your oil levels often.
An oily engine is a pretty good sign your engine is leaking oil, so open the hood and get a closer look. Excess greasy components could indicate seepage from several areas within the engine. The last and final indication that your car is leaking oil is the smell of burning oil. Because the engine gets so hot, when oil leaks onto various surfaces of the engine it burns and emits an unpleasant odor.
The severity of an oil leak can depend on the size and location of the leak. A serious leak will deplete your oil levels faster and possibly lead to serious engine troubles. Even smaller leaks can prove detrimental depending on their location. A leak at the front crank seal or timing cover will reduce the vitality of the timing or engine drive belts. A leak at the valve cover gasket will cause oil to fall onto the scalding exhaust manifold, which increases the possibility of smoke or fire.
Items located underneath your car are vulnerable to road debris and can be easily damaged. The oil pan, for example, is located at the bottom of the engine and is used as the reservoir for cleaning, lubricating, and cooling the engine. Punctures from rough roads or debris can cause the oil pan to leak. Often, the pan’s gasket that seals the pan succumbs to leaks due to wear and tear, cold and heat, and other road damage. These kinds of leaks are often difficult to locate and repair.
Valve covers are meant to keep the oil inside the engine and are secured with rubber or cork-like gaskets. Rubber products, especially in severe climates, wear out and become dry and brittle, preventing them from creating a proper seal, which results in leaks.
Located at the bottom of your vehicle’s oil pan is the drain plug. An essential component, this apparatus is removed hundreds of times throughout your car’s life in order to perform oil changes. A drain plug that isn’t properly aligned, overtightened, or that’s too loose at install can also cause leaks.
The oil filler cap is the area that has direct access to your engine for adding oil. To see if your car is leaking oil, remove the cap to check your oil levels. If the seal from the cap wears out, is loose, damaged, or missing, it will cause significant leakage. Inspect the condition of the seal when you check your oil and replace the cap if it is broken or shows signs of wear.
Over time, oil filters can wear out, loosen, or become misaligned. Going too long between oil changes can cause oil to become contaminated. Contaminated oil breaks down and causes degradation of seals and gaskets, which may also cause oil leaks. The oil filter is made to trap contaminants from the engine oil. Replace the oil filter with every oil change to ensure your engine is protected.
Leaking or worn-out engine valve seals or rings can deplete your vehicle’s oil level. The seals are engineered to prevent oil from leaking out as it travels around the camshafts and valves. Often unseen, these leaks can result in engine misfires or other serious engine troubles.
In order to fix an oil leak, the leak must first be identified. Though there are several items on the market to help resolve oil leaks, the best way to ensure the issue is resolved is by taking your vehicle to your local service center.
Identifying the primary cause of the leak is crucial to your engine. However, not all oil leaks are visible. For that reason, it’s imperative that you check your engine’s oil levels often between oil changes:
No matter the cause, it is imperative to fix an oil leak as soon as one is identified. If you notice your car is leaking oil when parked, see oil on the engine itself, notice a smell of burnt oil or smoke, or notice falling oil levels, bring your vehicle to the nearest Sun Devil Auto. By being proactive and repairing the leaks sooner rather than later, you may be able to prevent major engine damages.
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FOUNDED IN 1993
China SBT Oil Seal is an international company integrating design, research and development, production and processing.
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Won many honorary certificates through a number of patented inventions
