The rear main seal is crucial in retaining the oil within the engine and blocking any leakage from the crankshaft into the transmission.
Generally, the transmission has to be taken out first to reach the seal, which can be very expensive.
While the value of a rear main seal alone ranges from $20 to $80, the cost skyrockets if you pay a mechanic to do the work. Rear main seal replacements are difficult and labour-intensive; therefore, most mechanics will charge about $600 to $900 for the service.
If your vehicle suffers a breakdown of the rear main seal, it’s possible to bypass the extensive repair—this is, of course, dependent on the subsequent damage.
Continue reading for details on what a rear main seal consists of, the symptoms of failure, and the various approaches for dealing with rear main seals that have surpassed their useful life.
What Is a Rear Main Seal?
The rear main seal is the seal located at the end of the crankshaft and attached to the transmission, Its purpose is to stop the loss of oil.
A rear main seal is also sometimes referred to as a rear crankshaft seal, for it sits on the rear side of the engine where the crankshaft meets the transmission. The seal ensures the engine oil does not spill out through the crankshaft. The crankshaft is subjected to a significant amount of strain by your vehicle.
It contains the pistons and is linked with the flywheel and the pulleys that drive all the engine accessories. Because of the torque and strain applied to the crankshaft, it has several main bearings to support it.
These main bearings support the crankshaft and allow motion to be performed on it, while also enabling oil flow to the crankshaft.
This ensures lubrication and prevents damage from friction. The rear main seal is positioned externally to the rear main bearing, and its purpose is to retain oil. Typically, the seal is made out of silicone or rubber, and it is abraded as a result of friction between the seal and the crankshaft.
Operating an engine with low oil will prevent adequate lubrication from reaching the rear main seal, which in turn, increases the torque on the crankshaft seal, resulting in weakening the seal, which contributes to causing oil leakage.
What Happens When the Rear Main Seal Fails?
An oil leak is likely to occur from the rear main seal, camshaft oil will gradually leak into the transmission bell housing.
While the rear main seal does not intrinsically cause significant or destructive problems for the engine, the leaks that it does cause can give rise to issues that are much more serious.
Severe damage to the seal can result in rapid oil discharge from the reservoir, which can quickly lead to internal engine breakdown.
In most other cases, there is a slow oil leak from the rear main seal, which tends to worsen over time.
While we strongly advise dealing with a malfunctioning seal, we do understand the reasons behind delaying repairs since they do not pose an immediate threat.
From a favorable point of view, the only requirement when replacing the rear main seal is to detach the transmission. However, depending on the engine’s orientation, it may also be necessary to take out the oil pan or the entire engine.
In this case, the repair can be very expensive and may require considerable time before you are ready to deal with it.
Signs of a Leaking Rear Main Seal
Rear main seal leaks symptoms can be many, some being more obvious than others. Recognizing these symptoms will help you in devising a diagnosis at the earliest, which results in fast repair.
The following are the most popular symptoms of a rear main seal leak.
#1. Puddling of Oil in Driveway.
The level of an oil leak from the rear main seal greatly increases when the engine is hot. In this way, a leaking seal can be noted from several puddles that form at the bottom of the rear cap seal after the engine gets hot.
As a result, oil pooling on the surface of the engine bay also increases while the engine is running.
A sudden emergence of a new crude or refined oil pool mark in the yard can be considered highly suspicious and investigated closely, while an oil pool can develop gradually.
#2 Need For Frequent Top-Offs.
It is well known that a rear main seal leak can result in rapid oil loss. In extreme scenarios, a failed rear main seal can leak up to one quart of oil in a week.
This rapid leakage will require frequent top-offs to prevent the engine’s oil from dangerously depleting.
Should a weekly check of your vehicle’s engine show greater than expected oil consumption (for example, seeing a sudden need to pour oil into the engine at an unexpected quantity), a worn rear main seal is a potential culprit. It is important to allocate more time to examine this unusual situation of rapid oil depletion.
#3. Oil Saturation of Vehicle Underbody.
There are multiple reasons to help aid the claim that oil has leaked to the bottom of the engine and is being trapped inside the bell housing; this is also known as the class caver.” These are the gaps in the rear midshaft that form a triangle when viewed from the side.
Top pleasuring bound rings provide one with the ability to cap a rear seepage interface to restrict oil movement. The top caver binds the cap offer oil which extends between the test that surrounds the caver.
This puts greater emphasis on routinely checking your vehicle’s condition. In most cases, just looking under your vehicle will uncover tell-tale signs of rear main seal failure. This enables you to strategize for appropriate repair before the injurious leak becomes worse.
#4. Illumination of Oil Light.
When you are driving and suddenly the low oil light comes on, there are two crucial actions you need to take.
The first is to get your vehicle to the side of the road and switch off the engine immediately. The second key action is to determine where the oil in your engine has evaporated. A scenario like this would have a rear main seal as a likely culprit.
Severe leakage from a rear main seal results in exorbitant loss of oil, particularly when the engine runs at optimal temperature and the vehicle is in motion. There is a threshold limit that, if surpassed, oil loss will trigger a low oil warning light on the dashboard of the vehicle.
Simultaneously, surges in oil loss can turn on the low oil pressure indicator for some vehicles.
Causes of Rear Main Seal Oil Leaks
Usual rear seal issues and other activities can lead to an oil leak or failure. While some failures are natural, others are not.
Natural Wear and Tear
Wear and tear usually increase due to the constant movement of the crankshaft. Thus, seals begin to leak.
This will lead to fractures, which will start to leak and then worsen with time.
Individuals with gradual and slow fractures are most likely to be suffering from consistent grinding over the years.
A small seal yet expands is gushing due to the continuous rotational movement is most likely caused by a passive approach.
Efficient planning is the finest approach to postponing the product-specified period.
In most cases, it resolves upon completing an oil or filter change, or engine oil refill.
Worn Main Bearings
A main bearing not only helps position the crankshaft but also enables it to rotate in a certain direction.
Not only do main bearings, but also beefy support imposed and supple forces on a crankshaft that can wear the central section of the bearings down.
Once these bearings start wearing, some slop is created in the crankshaft, along with the ability for it to move or wiggle ever so slightly.
This causes additional force on the main seal, putting stress that causes rapid failure.
Unfortunately, the wearing of the main bearings resulting from this would also lead to multiple issues about performance and would, in turn, require a new bearing alongside a potential new crankshaft.
Because of this bearing’s position, it would need an entire disassembled engine, turning the repair into a pricey endeavor.
Low Oil Levels
When oil is at a low level, different parts of the engine are deprived of lubrication and oil.
At low oil levels, it results in excess friction and heat within the engine, which has a greater cost on the rubber seal, causing it to loosen and break.
Lack of oil is not recommended because of the multitude of issues that arise with worn main bearings.
Clogged PCV Valve or Failure
During normal operations, the engine produces blow-by gases, which occur when oil, gas, or exhaust can get past the piston rings and enter the crankcase.
Responsible for venting said gas is the PCV valve, which sends the bad gas back into the intake for mixture to be combusted.
This releases some of the pressure that is built up in the crankcase and reduces emissions.
A building pressure in the engine results when a bad PCV valve stops the blow-by gas from escaping the crankcase.
The excess pressure forces the rear main seal outward, which may result in it jettisoning from its position. This breaks the seal formed between the crankshaft and the transmission.
Eventually, this will cause an oil leak.
Crankshaft or Transmission Misalignment
If the crankshaft is not properly aligned, it will not rotate in a circular motion, causing excessive wear on the rear main seal.
Furthermore, the input shaft for manual transmissions and flex plates for automatic transmissions may also be misaligned or broken, causing undue strain on the seal, which makes the seal fail.
These problems arise less frequently unless recently one had a transmission or crankshaft altered, posing the risk for misalignment during the installation.
Is a Rear Main Seal Leak Serious?
All put together, rear main seal leak is considered serious because such leaks are known to exacerbate over time.
In critical instances, a rear main seal can leak to such an extent that attempts to contain the resultant oil loss become challenging. In other words, it becomes difficult to add oil to ensure the lubrication system functions adequately.
Nonetheless, this remains a better situation than what will likely happen if an engine becomes neglected and runs out of oil because of a rear main seal leak. Considerable and uncontrolled loss of lubricating oil poses bearing damage, include spun bearings, which can result in catastrophic engine failure.
Essentially, running an engine on a low oil reserve results in unnecessary internal wear. Equally important, a rear main seal leak needs to be fixed at the earliest opportunity is given.
While this type of leak can require extensive work to fix, it is nowhere near the degree of difficulty as dealing with an engine that has been drastically damaged after suffering from a lack of oil over extended periods.
If performing such repairs is not in your skill set, which will be the case for many people, reach out to your local service center for an appointment or a trusted place to take your vehicle to.
Can You Replace the Rear Main Seal Without Removing the Transmission?
Usually, a rear main seal’s replacement entails the disassembly of the vehicle’s transmission. This step is key in order to access the rear main seal which is located at the back of the engine, within the bell housing of the transmission.
Sadly, transmission removal is a complicated and lengthy procedure.
Fortunately, several products claim to immediately stop a rear main seal leak. These products literally attempt to ‘rehydrate’ an aging seal, thus enhancing the sealing capabilities instead of reducing them.
Unfortunately, this category of products is associated with varying levels of success, which is why many consumers choose to avoid them.
While a majority of these products prove to be unhelpful, a few tend to stand out due to the overwhelming positivity they receive from consumers. One such product is BlueDevil Rear Main Sealer, which is often cited by consumers as being a “cure-all” for rear main seal leaks.
In any case, the consumers do not have much to lose by trying a rear main seal stop leak product. After all, when other options include excessive downtime for the vehicle and exorbitant costs associated with repairs, the use of a single-application sealant is a breath of fresh air.
Cost of Replacing Rear Main Seal
There is no sugar-coating the fact that a rear main seal leak will turn out to be repair-worthy in terms of costing you quite a bit. The additional hassle is that the rear main seals themselves are quite inexpensive. However, the associated costs of labor in carrying out the repairs is often very high.
In any case, there is valid justification for these labor costs. Replacing an engine’s rear main seal is no cakewalk. It involves a lot of time, which is costly for most.
To repair this nature, you will require the removal of the vehicle’s transmission. Otherwise, there is no way to access the rear main seal of an engine. In the case of four-wheel drive vehicles, the transfer case will have to be removed too.
Rear main seal replacement pricing differs among vehicles and is based on a manufacturer’s suggested labor time for the repair. Furthermore, pricing for rear main seal replacements also varies depending on the drive configuration of the vehicle.
The cost for rear main seal replacement is somewhere between $650 and $1800, however, most repairs typically cost between $800 and $1200.
Will Thicker Oil Help a Rear Main Seal Leak?
In some cases, using thicker engine oil may reduce the rate of oil loss through the rear main seal. This may be because oil becomes less viscous when it is heated during normal engine operation.
Consequently, oil tends to flow more freely through aging, worn, or damaged seals. This is one reason why the leaking rear main seal seems to get worse when an engine is at operating temperature.
Given this, one can assume that oil that is of greater warmth would be less likely to leak from such a seal and would remain in the cavity. It is safe to say that most people have heard from someone who would claim that their oil leak was reduced by changing the oil from 10w30 to 10w40.
It has become customary to come across claims suggesting the use of heavier diesel engine oils, like 15W40, in gasoline engines to mitigate a misfire.
Also, the consequences of straying from the manufacturer’s guidelines on mileage and oil viscosity should be weighed. Several reasons justify the use of a particular viscosity of oil, and one includes the measurement of an engine’s bearing tolerances.
Oil selection with certain changes, although highly unusual, could result in issues with oil delivery. Altering the viscosity of oils from their recommendations, regardless of the vehicle, evokes hesitation.
Rear Main Seal Replacement Options
To effectively fix a leak, the rear main seal needs to be replaced. That would be the ideal option.
As we’ve discussed, replacing the part can be quite inconvenient.
If your invaluable vehicle needs a quick temporary fix until you can afford a comprehensive solution, consider the alternatives that don’t break the bank.
We recommend not touching the DIY solutions below until you get professional advice and a thorough assessment done at a garage for the issue.
Use an Oil Additive
Oil additives like BlueDevil’s Rear Main Sealer directly fix gaskets and seals by adding them to the oil of your vehicle’s engine.
The Hydraulic Pump Sealant expands the seal, which causes an internal seal to burst, so the leak would get sealed off.
This method applies to all rubber seals, regardless of whether they are fractured, desiccated, or misshapen and warped.
If the seal continues to deteriorate and leak further, additional application is possible. While it is a short-term remedy, it does not provide a long-lasting solution.
For less precious, and dilapidated cars, other means would be more expensive compared to a seal replacement. For these cars, this $20 fix is ingenious.
Use a Thicker Engine Oil
With age, slimmer oil leaks may slacken, but switching to thicker oil such as 10w-30 could slow down the leaks significantly when substituting from 5w-20.
Of note, using seal repair and multi-purpose additives mentioned previously warrants better results alongside these alternatives.
In a wider perspective, these acts can only help postpone the need to fix the rear main seal. Consider visiting your local garage after carefully contemplating these measures in advance.
A professional garage will inspect the vehicle to locate the problem. In case of a rear main seal change, they will provide a clear quote for the replacement.