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.

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


27 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!


    1. Jose,

      Thanks for your question about your 2000 Silverado. We’re assuming you’re talking about the rear main seal on your engine which is not an easy job. First, we would recommend using BlueDevil Rear Main Sealer (available here: to try and stop that leak first to save yourself the time and money. The basic procedure to replace the rear main seal on your engine will include removing your transmission and flywheel to get to the rear main seal. You may also have to remove the engine oil pan to be able to replace the seal.

      Thanks again for your question!
      -BD Auto Pro

      1. Will blue devil help if its pouring out fast did oil change think wrong oil was used now its pouring out when i start my car didnt have no leaks before this at all

        1. Raymond-

          BlueDevil is intended for leaks that are seeping or lightly dripping. Based on your description, unfortunately, it sounds as though you are losing oil too quickly for the product to be able to seal the leak. Replacing the seal may be your best option.

          Thank you!


  4. My clutch goes to the floor and won’t go In gear. Was told my rear main seal was leaking that caused me to need a clutch flywheel and bearings. Will this product help

  5. I am truly amazed after trying 3 other products claiming to stop my rear seal leak one of them costing over $100.00.None of them worked period.As I was planing a trip of around 800 miles my neighbor who is a mechanic reccomended blue devil.I added it right before my trip along with the gas additive.Got home from my trip and I couldn’t beleive it.NOT ONE DROP ON GARAGE FLOOR.Thank You Blue Devil for saving my precious 2001 Mustang Convertible.

    1. Peter-

      That is excellent to hear! Once the product seals, it would be a permanent seal, so you should be good to go at this point. We appreciate your positive feedback.

      Thank you!


  6. If I dtive at freeway speeds for about 40 miles I’m down about 2 quarts. Will your product help?

    1. Jason-

      Unfortunately, you may be losing oil a little too quickly for the BlueDevil Rear Main Sealer to be successful. Typically, you would expect to see results after approximately 100-200 miles of driving. Based on your description, you may lose the product before it gets a chance to seal. A hard part repair may be your best option.

      Thank you!


  7. Hi…would it be dumb to add a bottle of rear main sealer to a higher mileage vehicle as a preventative measure even though nothing is leaking yet just to maybe help restore the seal before it has a chance to start leaking?

    I’ve used BD head gasket sealer for head gasket and once for a heater core so I’m impressed with your products. Thanks

    1. Dave-

      The BlueDevil Oil Stop Leak would be the better choice to use as a preventative maintenance, as the Rear Main Sealer would only be treating the rear main seal. Either way, the product does not harden or thicken in anyway, so it would not cause any adverse effects on the engine.
      The product would revitalize and recondition the rubber seals/gaskets and keep them from becoming brittle, so it would be a good idea to utilize the Oil Stop Leak as a preventative measure.

      Thank you!


  8. my care is 2011 with 81,000 miles and suppose to have a rear seal leak…nothing on the garage floor—but the engine is using to much oil now and in the garage getting fix …..should I have them fix it now while having the engine torn apart or wait? thanks

    1. Betty-

      What is the work you are having performed? Are you having the rear main seal replaced? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


  9. I have a 97 dodge ram 5.9 L with almost 350k miles. Everytime I return to my truck after driving it I notice about a quarter size drop of oil on the ground and there is a thin layer of oil on the bottom of my oil pan and where my trans meets up to my engine. I usually have to add about a quart of oil once a month to the engine. I have replaced the rear main seal 3 times myself due to it being a fairly easy job in this particular truck. My question would be if I use blue devil is it going to gunk up my engine cooling holes, heater core lines, or other lines in the cooling system or engine. This is the only reason I have not used any type of stop leak additives as of yet. Even though it only takes about an hour for me to replace the rear main seal I have grown tired of doing that job only to have it become a problem again within a few months. Also what does the guarentee cover.

    1. Joseph-

      Thank you for asking about your Dodge Ram. The BlueDevil Rear Main Sealer does not contain any solid or particulate matter, it is purely a liquid. The product does not harden or thicken in any way, so it would not cause any adverse affects on the engine or the system itself. There is a money-back guarantee on the product. If it is unable to seal for whatever reason, you are able to contact us and be refunded for your purchase. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


  10. Good day.

    I have changed my rear main seal 3 times now in the last 2 years and its still leaking. I even had the crank measured and inspected for smoothness or any grooves that might have been made by the oil seal. And still oil is leaking…. I’m at a loss for options. The leak is about the size of my Palm overnight. Would ‘BlueDevil help or is there a different problem I might be missing?
    I’m desperate to find a fix, its embarrassing to mess oil onto someone else’s drive every time. Plus I can’t afford to change it again, the cost at time is killing me…..

    Please Help.
    Wessel van Niekerk

    1. Wessel-

      Based on your description, it would be worth trying the BlueDevil Oil Stop Leak. The product is 100% safe to use. It does not harden or thicken in anyway, and would not cause any adverse affects. You should expect to start seeing results after 100-200 miles of driving.

      Thank you!


  11. Hi, I took my Jaguar XF for an oil change a few weeks ago and they said they noticed my rear crankshaft seal needed to be replaced since oil had leaked all over. It’s a diesel car. Is it okay to try the blue devil oil stop leak before I consider changing the rear crankshaft seal. The car only has about 50k miles

    1. Asha-

      Thank you for asking about your Jaguar XF. Yes, the BlueDevil Oil Stop Leak would be safe and compatible to use on your vehicle and would be able to treat a leaking crankshaft seal. You should expect to start seeing results after 100-200 miles of driving.

      Thank you!


    1. Sammy-

      BlueDevil Oil Stop Leak is more concentrated and is the universal application that will work for various leaks such as oil pan leaks, rear main leaks, valve cover gasket leaks, etc. Whereas the Rear Main Sealer is less concentrated and specifically formulated exclusively for leaking rear main seals. If you are not 100% sure where the vehicle is leaking or there seem to be multiple leaks then we recommend using BlueDevil Oil Stop Leak. It is not necessary to add both products simultaneously.

      Thank you!


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