Rear Main Seal Leak – Symptoms, Reasons & Repair Costs
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If you’re driving and notice a strange noise, it’s probably best to take your car to a mechanic and get it checked out. One common issue that mechanics see is a rear main seal leak. A rear main seal is a gasket that seals the engine block and the transmission. If this seal leaks, oil can leak onto the ground.
This blog post will explain what causes an oil leak from the rear main seal and how it can be fixed. We’ll also discuss some of the symptoms of a rear main seal leak so that you can know when to take your car in for repair.
What is a Rear Main Seal Leak?
A rear main seal is a rubber gasket between the engine block and the transmission. Most cars have a rear main seal because it prevents oil from leaking out of either location. Losing oil from the engine is always bad, and in a worst case can lead to engine damage.
When an engine starts, it creates a vacuum effect as air rushes to fill the cylinders. This suction can make oil move outside towards other parts of the engine. A rear main seal – or rear crankshaft seal – prevents oil from leaking past the crankshaft, which might drip onto the ground and in some cases also end up in the clutch.
If oil leaks out of an engine, it cannot be very good for a car with manual transmission. If you have ever driven down a dirt road, you know that oil on the ground can create some slippery conditions. It can be hazardous if you are on the road. If oil leaks out onto the road, it can reduce traction and cause your car to lose control. Additionally, rear main leaks can damage the engine, if too much oil is leaked from the engine.
If your car has a rear main seal, you will most likely notice an oil spot underneath where you park it. This oil spot might increase over time depending upon how often you drive your car. If you see an oil spot underneath your car, it’s a good idea to take it in for repair as soon as possible.
Oil leak on a car doesn’t always mean the rear main seal is leaking – it’s also possible the engine oil pan or valve cover gasket is leaking – but nevertheless, oil leak is never a good thing and should be checked as soon as possible.
Symptoms
There are several symptoms of a rear main seal leak, and they can vary depending upon the severity. The most common symptoms are explained below.
Oil Puddles
If you notice an oil puddle under your car, it could indicate a rear main seal leak. If the rear main seal leaks, oil might drip out of the engine and the leaking oil can create a puddle below it. Sometimes this oil is dripping directly onto the ground. However, other times it will wick onto nearby objects like your tires or even your driveway.
Puddles will typically form right where your car is parked. If you notice an oil puddle under your vehicle, it’s possible that the rear main seal has failed and needs to be replaced.
Oil Burning
If your car smells like burning oil, it could indicate a problem with the rear main seal. The burning smell will become more apparent when you start driving your car. If the rear main seal fails, it can cause oil to enter your exhaust system. As you go, oil could burn onto hot exhaust components, which will increase the smell.
Oil leaking out of an engine can be problematic for a manual transmission vehicle. Manual transmissions have many moving parts that are exposed underneath the car. If oil drips down and soaks into these parts, it can cause them to fail. If your manual transmission has a rear main seal leak, it will eventually destroy the clutch and the differential. The oil that leaks onto the clutch or differential can cause components to slip and even break completely.
Therefore, even though rear main seal repair can be expensive, it’s usually worth the price. If you don’t fix it on time, you might end up paying for a much higher price on other repairs later on.
Rough Driving
If you notice that your car makes unusual noises, it could indicate a main seal leak. Depending upon how bad the problem is, your car might vibrate and make odd noises while you drive.
The loudest noises will come when your car idles in gear. Oil may be dripping onto hot engine components if you hear grinding, popping, clicking, or other sounds while idling. These sounds can become more noticeable as you accelerate your car above 20 miles per hour.
If you hear any strange noises from your car, don’t drive any longer. Get your vehicle checked immediately.
Smoke From the Vehicle
If you notice dark smoke coming from your exhaust, it could indicate a rear main seal leak. Since oil leaks are pervasive in older cars, many mechanics tell customers that they’re smelling burning oil when their car leaks smoke. However, this isn’t always the case.
The oil that drips out of the engine can be drawn into the exhaust manifold. If the rear main seal is leaking, it can cause oil vapors to enter the exhaust system. This will cause smoke to come out of your tailpipe even if you don’t have a problem with burning oil.
Other times, oil vapor can build up inside the engine compartment and eventually push through cracks in hoses or gaskets. This is especially common with older cars with rubber hoses that are starting to deteriorate. If you notice smoke coming from your vehicle, it’s possible that the rear main seal has failed, and oil vapors are entering the engine rather than dripping out of it.
Accumulation of Debris
Once the rear end differential has failed, your rear main seal will start to drip onto it. This will cause oil to accumulate underneath your car and eventually lead to debris getting stuck inside the axle.
If you see a lot of rust or other junk under your car, it could indicate that the rear main seal is leaking. It can be challenging to remove all of the debris without taking apart the rear-end assembly when this happens. This is because oil has soaked into the differential, and rusty pieces of metal will stick to it when you pull it out.
Causes of Rear Main Seal Leaks
If you notice any of these problems under your car, it could indicate a main seal leak. Depending upon the severity of the problem, you might be able to get away with fixing just this one part and saving money on labor and parts costs. However, if you ignore these signs and the fluid leaks continue, you may need to replace your transmission or even your engine.
Condition of Engine Oil
The condition of your engine oil can be one of the causes of rear main seal leaks. If the leak is small, you might get lower oil levels than usual. This can result in poor lubrication which can break the engine. However, there are some cases where the rear main seal causes so much oil loss that it creates a gushing waterfall underneath your car.
If your oil is dark and has a burnt smell, you might have a leaking rear main seal – or other problems on your car. If this is the case, you’ll need to fix the problems as soon as possible or risk total engine failure from lack of lubrication.
Main Bearing Is Worn Out
A worn-out main bearing can cause a main seal leak. You can’t see it with your eyes, but a worn-out main bearing can create an excess play that will allow the engine to wiggle under high RPMs. This extra movement is also known as rattling and is very common with older cars.
If this sounds like the case under your car, you need to have the rear bearing replaced immediately, or you may damage other components in the engine. The role of the rear main bearing is to support the crankshaft while it spins. If the bearings are worn out, it will cause a lot of stress on other engine parts, which can damage them and even cause them to fail early. Engine failures are always expensive, so the problems must be fixed on time.
Defective PVC System
A failing or clogged PVC system can also cause a main seal leak. This is especially common with older cars with exhaust gas recirculation valves (EGRVs). When these EGRs fail, they can allow so much pressure to build up inside the engine that it starts to push out around the gasket.
To fix this, you need to have your EGRV professionally repaired. If it isn’t fixed, the excess pressure will continue to build up inside of your engine and can cause permanent damage or even an engine fire.
Bad Design
The design of the rear main seal itself can be one reason for leaks. Depending on your car’s model year, the rear main seal may be located in a very awkward spot. This can make it difficult to replace if you don’t have the right tools or knowledge about your car.
If you find that working on the rear end of your car is difficult, you may need to get an expert involved. It’s possible that someone who knows how to work on older cars could replace the rear main seal in just a few hours.
Crankshaft Condition
A worn or corroded crankshaft is another cause of a main seal leak. This occurs when the oil seals inside the engine wear down from too much movement. If your engine has been making excess noise for a while now, you might want to have it inspected as soon as possible.
In some cases, people will try to get away with just replacing the rear main seal. However, the crankshaft needs to be inspected for you to determine if it is worn too thin. If so, it will need to be replaced instead of just having your seal replaced.
You can identify the leak by adding dye to your oil and checking for oil spots on your garage floor. Another way to check is to remove your oil filler cap while driving (after allowing it to get good and hot) and see if any steam or smoke comes out of there. You will need a special light to identify whether the smoke is blue or white. Any smoke that is not blue means that you leak your engine.
Misalignment Issues
A leaking rear main seal can also be caused by the incorrect alignment of your engine parts. If you hit a large enough bump, it could knock the flange on the crankshaft out of place and misalign the flywheel.
This can cause a leak because it changes how well your gasket holds all of that oil inside your engine. You can usually identify this type of leak by seeing if the oil is running down the bell housing, cylinder head, or even the dipstick tube.
If you suspect that your rear main seal is leaking because of misalignment issues, then you need to check with a professional as soon as possible. Especially if you hit that bump somewhat hard, these types of leaks are complicated to repair, so the best thing you can do is get your alignment checked out.
Seal Coating
The seal coating of your car’s rear main seal is also an issue that can cause it to fail early. This usually happens because the factory didn’t use high-quality materials when they coated your gasket.
Some of the most common signs of this are leaks, engine noises, or even excessive oil consumption. You might be able to catch this if you notice oil on your spark plugs and smoke coming out of the exhaust.
Before the seal coating fails, your best bet is to get it replaced as soon as possible. Most people don’t realize that these gaskets can be coated and wait too long because they think that oil leaking from their engine is standard.
Rear Main Seal Repair Costs
Depending upon the year, make, and model of your car, you will end up paying anywhere from $150 – $350 for a replacement rear main engine seal. Some cars require removing or replacing other parts to get to them. For example, if it is located on top of the firewall, you need to either remove the intake manifold or the transmission.
Nissan is known for having rear main seals in awkward places, so you may have to remove a couple of parts to get to the engine block. For example, you may need to take out both your exhaust manifolds and your oil pan before you can even get started removing that seal.
You could end up paying just as much for labor as you do for the actual rear main seal. This is because most mechanics will charge $100-$150 to install it, and then they will tack on another couple of hours if you end up taking out certain parts before getting to it.
If you like the idea of replacing the rear main seal yourself, you will have to buy the part elsewhere. Some places are much cheaper than others. The best thing that you can do is find a mechanic and ask them to see if they think that your rear main seal needs to be replaced or not.
Tell them what symptoms you’ve been experiencing, and then let them check the oil level, crankcase pressure, and any oil on the dipstick. After they tell you what to do, feel free to fight them on it and replace the seal if that is what you want to do.
FAQs
How Serious Is the Rear Main Seal Leak?
The rear main engine seal is usually one of the first parts to go when your car starts having more extensive issues. They are especially dangerous because they cause oil to leak out your engine. This can be very dangerous if you have other serious problems causing the same type of issues.
How Do I Know If I Have a Main Seal Leak?
The first step is to check your oil and see if it looks like it has been leaking. You will usually find oil on the dipstick, exhaust manifolds, or even down by the ground under your car. The next thing you can do is listen for any strange noises that sound like they may be coming from the rear of the engine. Oil leaks are not always caused by failing main seal; for example, leaking oil pan gasket can also cause oil leak from the engine.
How Long Does It Take to Replace a Rear Main Seal?
It takes around 2 hours, on average. You will have to remove both exhaust manifolds and the oil pan before you can even start removing that rear main seal from your engine block. The labor costs for this will add up very quickly because most mechanics charge $150-$350 for this service.
How Do I Get This Fixed?
If you suspect that oil leak is caused by failing main seal, you can check the oil level crankcase pressure or inspect the oil on the dipstick. If it looks like there are any issues with it, then take your car to a mechanic (or try to replace it yourself) as soon as possible.
Where Is The Rear Main Seal Located?
The rear main seal is usually located right around the middle of your car. It can be between the front and back axles on some models, in which case you will have to remove your transmission to get to it partially. Even if they’re easy to access, most cars still require you to take out both exhaust manifolds and the oil pan before you can even get started removing that rear main seal from your engine block.
The rear main seal is usually the first thing to go when your car starts having more prominent issues. The rear main engine seal is especially dangerous because they cause oil to leak out of your engine. This can be very dangerous if you have other serious problems causing the same type of issues.
If you suspect that your rear main seal is leaking, you can check the oil level crankcase pressure or inspect the oil on the dipstick. If it looks like there are any issues with it, then take your car to a mechanic (or try to replace it yourself) as soon as possible.
