How Did My Car Get a Rear Main Seal Leak?

Rear main seal leaks are one of those dreaded problems with your car that are hard to understand and even harder to fix.  A rear main seal leak can sometimes be the last nail in the coffin for an older car with a few other problems, or an expensive repair that leaves your bank account on “E”.  In this article we’re going to look at what it is that causes a rear main seal leak so you can try to avoid it, but we will also look at your options if you already have a rear main seal leak.rear main seal leak

Your rear main seal is the seal that is just outside of your rear main bearing.  The crankshaft for your motor is supported by the main bearings 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 absorb the axial load of the piston being forced down by combustion while still allowing the crankshaft to spin therefore creating the rotary motion of your engine.

To accomplish the task of absorbing all that load and still allowing rotation, these bearings have to be incredibly smooth and stay well lubricated by the oil in your engine.  The correct oil for your engine is extremely important in creating the right environment for the bearing to do its job without wearing out.  This oil also has to be contained within your engine so it can continue to do its job keeping things lubricated.  This is where your rear main seal comes in.  The rear main seal allows the crankshaft to exit your engine case so it can bolt to your flywheel or flex plate and transfer its energy into your 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.

If you’ve got a rear main seal leak then your rear main seal isn’t doing its job and you’ve got a problem.  Rear main seal leaks can happen for a variety of reason:

  • Low engine oil levels
  • Excessive heat
  • Worn main bearings
  • Old age
  • Infrequent use
  • High mileage

Any of the above conditions can cause your rear main seal to leak because they can deform or deteriorate your rear main seal.  If your vehicle has worn main bearings, the rear main seal can actually leak because the crankshaft is able to move excessively inside the bearings which will stretch and move the rear main seal while the engine is running allowing oil to leak past the seal.  This could be the case from simple wear and tear if your engine has high miles, or it could be due to a low oil level or using the wrong type of oil.  It is difficult to tell if your engine has worn main bearings without removing a lot of equipment, but if this is the case with your car, you’re most likely in for a full engine rebuild which would including removing the motor and replacing a lot of components, including the rear main seal.

rear main bearing leakIf you have a leaking rear main seal due to high mileage, old age, or infrequent use then we have great news!  BlueDevil Rear Main Sealer can bring your rear main seal back to life and seal your leak.  BlueDevil Rear Main Seal is safe to add to your engine oil and can revitalize and restore your rear main seal to its original size, shape and softness so it will again seal around your crankshaft and keep your engine safe and leak free.

BlueDevil Rear Main Sealer

For more information about BlueDevil Rear Main Sealer, check out the product information page here: Rear Main Sealer

When you’re ready to seal your rear main seal leak, visit any of our partnering local auto parts stores to pick up a bottle of BlueDevil Rear Main Sealer today!

  • AutoZone
  • Advance Auto Parts
  • Bennett Auto Supply
  • CarQuest Auto parts
  • NAPA Auto Parts
  • O’Reilly Auto Parts
  • Pep Boys
  • Fast Track
  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributer
  • DYK Automotive


Pictures provided by:

main_bearings.jpg – by VX1NG – Licensed By Creative Commons Via Wikimedia – Original Link
rear_main_bearing.jpg – By Andrew Davidoff – Licensed by Creative Commons via Flickr – Original Link


5 responses to “How Did My Car Get a Rear Main Seal Leak?

  1. Just wanted to let you guys know that I used your blue devil rear main seal stop leak on a 2004 Jeep Grand Cherokee that I bought with 157,000 miles on a 4.0L inline 6 engine. It indeed stopped the leak (about dime to penny size puddles at every stop and oil allover the transmission pan) after about 2 days of driving. I’m going on 6 weeks now running full synthetic without any recurrence of the leak. Thanks for making a great product.

  2. Hi I did your rear main sealer a few weeks ago and I think it may have helped. Would using the regular oil sealer be redundant now? Thanks.

    1. Taylor-

      We are glad to hear of the success you have had with the BlueDevil Rear Main Sealer. If you are no longer seeing a leak, it would not be necessary to use the Oil Stop Leak at this point. If you are still seeing somewhat of a leak, the Oil Stop Leak may be an option for you. Please contact our technical support line at 888-863-0426 so that we can get a better understanding and be able to make any appropriate recommendations.

      Thank you!


  3. Hello, I added Lucas Rear Main Seal stop leak to my Chevy 5.3 (148k miles) and it slowed the leak somewhat, but not too much. I added Blue Devil and am waiting to see what happens. Is mixing the two different stop leaks bad for the seals? Does the seal stop leak hurt the non leaking seals in my engine (as I have read)?

    Thank you..

    1. Jack-

      BlueDevil Rear Main Sealer will not harm and seals, gaskets, or other components of the engine; it is 100% safe to use and the product carries a guarantee. Due to the fact that you have already added a different additive we recommend that you wait until your oil is changed to add BlueDevil Rear Main Sealer. Once the product is added you can expect to start seeing results after about 100 miles of driving.

      Thank you!


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