The rear main seal is an essential component that prevents oil leaks. This seal is susceptible to cracks and damage due to normal wear and tear over the course of your vehicle’s life. If you see oil puddling underneath your car or truck, it may indicate a problem with the rear main seal.

What is a Rear Main Seal?

The rear main seal is a gasket (seal) that forms a tight connection to keep oil inside the engine’s rear. These seals are typically made from synthetic rubber, nitrile, silicone, Viton, or PTFE rubber.

The rear main seal is located at the point where the crankshaft connects to the transmission. The seal itself is not big, and it’s quite simple. However, it’s a very important component that does an essential job. 

Over time, the seal can become weakened, damaged, or corroded. With normal wear and tear, or due to harsh conditions, the seal can become compromised and result in a leak. Oil leaking from this area of the engine can cause bigger problems if it goes on too long without being repaired. 

A faulty or damaged rear main seal can lead to oil leaking onto the clutch in vehicles with a manual transmission. This can cause other problems, such as slipping and chattering. No matter where the oil is leaking, it’s important to address it as soon as possible. 

What Causes a Rear Main Seal to Fail? 

The materials that seals are made of leave them vulnerable to damage and wear over time. A vehicle’s age is the primary reason that the rear main seal may eventually fail and leak.

However, running the engine while it’s low on oil can also contribute to the problem. If the seal dries out, it can harden and shrink. Once the seal hardens, it’s very vulnerable to cracks, tears, and other damage. 

Other conditions contributing to a rear main seal leak include excessive heat (overheating engine) if the engine sits for a long time without running or high mileage on the vehicle.

Outside or environmental conditions can also cause the seal to wear out faster. For example, vehicles that frequently drive on roads treated with ice may find more problems with the rear main seal. 

Filling the oil level past the max fill line can also cause a leak. If the PCV (Positive Crankcase Ventilation) system fails, the pressure buildup that may occur inside the engine can cause an oil leak.

In these cases, the leak isn’t due to wear and tear due to the rear main seal failure, but the leak may occur from the same area. 

Diagnosing a Bad Rear Main Seal 

It can be challenging to diagnose a problem with the rear main seal because you won’t be able to see the seal itself. It’s not visible during your standard vehicle inspections. However, there are some common signs that are noticeable which may indicate a faulty rear main seal.

Oil Puddling Underneath Your Car

This is the main indicator that there could be a problem with your rear main seal. Oil puddles in your garage or driveway certainly indicate that oil is leaking from somewhere, but you’ll need to take it to a mechanic to isolate the source of the leak. 

Low Oil Level

Even if you don’t see pools of oil underneath your car, you could still have a leak. If your vehicle runs low on oil and you have to top it off in between your scheduled oil changes, it’s a likely indicator that the oil is leaking out somewhere. 

Sometimes, the oil doesn’t leak fast enough to leave visible pools for the owner to notice. If you have to add oil to your engine or you suspect you may have a leak, try parking your car in the driveway and letting it run for about 15 minutes.

Afterward, move your vehicle and look for signs of oil underneath. Sometimes, letting the car idle can reveal a small oil leak that you wouldn’t otherwise notice. 

How to Replace a Rear Main Seal 

It’s possible to replace the rear main seal yourself if you have the know-how and the right equipment. However, most people will need to leave this one to the professionals. If you decide to give it a try, make sure you at least have a helper to assist with the heavy lifting.

First, disconnect the battery. 

Next, jack up the vehicle. You really need to get the car up on a lift, if possible. You’ll need to inspect for leaks to make sure you’re working in the right area, and then you can start unbolting your vehicle’s transmission. You’ll need to use a transmission jack to safely remove the transmission. 

Remove the torque converter. 

Remove the flywheel. Locate the bolts that hold the flywheel in place and use a hammer to gently release it. 

Locate the rear main seal cover. Remove the bolts holding the cover into place, and then remove the cover. 

Remove the rear main seal. This part can be a little tricky. You may need to use a screwdriver to pry it out or get it loose. Take care not to damage the crankshaft or the housing around the seal. You may want to consider using a lip seal removal tool to make this job easier.  

Install the new seal. Take care not to damage the seal and ensure that it fits exactly. You may need to use a ball-peen hammer or driver to tap the seal into place all the way around. Run your finger around the seal to feel that it’s flush.  

Reinstall the cover. Once you’ve bolted the rear main seal cover back into place, you can follow the steps in reverse to put the flywheel, torque converter, and transmission back. 

Check out this video on YouTube to see a demonstration of how it’s done.

Cost Factors for Rear Main Seal Replacement

Most of the time, it costs between $650 and $850 to replace your rear main seal, but the price could be higher or lower depending on your vehicle and other factors.

The labor charge is the primary factor impacting the cost of replacing your rear main seal. Parts for the job are typically under $35, which means that labor costs around $700 on average. 

Labor costs may vary based on where you take the vehicle (for example, a dealership versus a local mechanic), the make and model, and your geographic location.

Whether your vehicle has a manual or an automatic transmission may also impact the price. The time of year can even influence labor costs. When the shops are very busy, supply and demand can increase the costs of goods and services.

The price for the seal itself may vary slightly depending on your vehicle and the type of seal that you purchase.

While the cost for the parts is a small percentage of the overall price, it can impact your total. For example, certain high-temperature engines may require a premium seal to withstand higher temperatures. As such, those types of premium parts are typically sold at a premium price. 

The best way to estimate how much it will cost to replace the rear main seal in your vehicle is to compare it to sample costs for other similar cars and trucks.

Since the price can vary quite a bit based on the make and model, seeing how much other people have paid for the work can help give you a better idea of what to expect. 

Of course, these costs are just to do the work for replacing the rear main seal itself. Other factors, such as additional repairs and work, may impact your final price. Sometimes, it makes sense to replace other components that are nearing their end of life while doing extensive labor.

Removing the oil pan typically means that you’ll need to replace the oil pan gasket. Other repairs may include replacing the front crank seal or clutch components. 

FAQs On Rear Main Seal Replacement Cost

Is it worthwhile to fix a rear main seal leak?

Whether fixing a rear main seal leak is worth it depends on several factors, such as the extent of the leak, the age and condition of the vehicle, and the cost of the repair.

A rear main seal leak can be a significant issue as it can allow engine oil to leak, which can result in reduced oil levels and potential engine damage.

However, if the leak is minor and the vehicle is in good condition, it may not be necessary to fix it immediately. Ultimately, the decision of whether to fix a rear main seal leak should be based on a careful consideration of the factors mentioned above and a professional mechanic’s assessment of the issue.

Can I drive with a leaking rear main seal?

It’s not recommended to drive with a rear main seal leak as it can lead to reduced engine oil levels and potentially cause significant engine damage. Engine oil provides lubrication and cooling for the engine’s internal components. A significant loss of oil can result in friction and overheating, which can cause serious damage to the engine.

If you’re driving a vehicle with a rear main seal leak, it’s important to monitor the oil level regularly and top it up as needed to prevent the engine from running low on oil. You must remember that this is only a temporary solution and that the leak should still be repaired as soon as possible.

How can the rear main seal be checked?

To check for a rear main seal leak, You must check the following points.
1- Check for oil on the ground
2- Clean the area around the rear of the engine
3- Check the oil level
4- Look for oil seepage

Can a rear main seal leak damage transmission?

Yes, a rear main seal leak can potentially damage the transmission. If engine oil leaks from the rear main seal, it can contaminate the clutch and transmission fluid, leading to slipping and other issues with the transmission. Over time, the oil can cause damage to the transmission’s internal components, leading to a need for costly repairs or even replacement of the transmission.

What causes seal failure the most frequently?

The most common cause of seal failure is age and wear. Over time, seals can become brittle and crack, leading to leaks. This is especially true for the rear main seals, which are subject to high levels of stress and pressure as the crankshaft rotates.

Rear Main Seal Replacement Cost: Final Thoughts

Oil leaking from your vehicle is never a good sign, but it’s typically something that can be repaired at any local garage. If the source is your rear main seal, it will probably need to be replaced.

Replacing the rear main seal usually costs between $650 – $850 but may run as high as $2,000 or more, depending on your vehicle and where you take it. 

Since the bulk of the cost is labor, you may be able to save a few dollars by shopping around. Getting a few quotes before deciding where you’ll take your car is a good idea. It doesn’t hurt to ask if the shop offers any discounts for things like AAA, senior citizens, students, or first responders. 

You can also do a web search to price out the parts before you take your car to the shop so you’ll know what to expect for that part of the estimate. Sometimes, the labor is more negotiable, especially if you have other work done at the same time.

If you need new tires, brakes, or other big jobs like a timing belt or water pump, it might be a good time to ask about adding those items to your estimate.

Be sure to consider the garage’s reputation, quality of work, and what kind of warranty they provide. When you consider these factors along with the price, you’ll be able to make the best decision for your situation and get the best value for your money.

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