Where is the Rear Main Seal?

Rear Main Seal LeakHaving a problem with the rear main seal in your vehicle can be a scary thing, mostly because many of us don’t entirely know what that seal is or does.  We’ve only heard horror stories about friends who had great reliable vehicles that developed a rear main seal leak and suddenly their car was only fit for a junk yard.  Here at BlueDevil we’re hoping to change that myth.

The rear main seal is a seal in your engine that is very important and usually difficult to reach.  If you pop your hood and start looking around for the rear main seal, you aren’t going to have much luck seeing it.  It is buried deep, usually under a lot of protective covers, wires, hoses and unfortunately, the bell housing of your transmission.  Let’s first break down the name to see what we can learn about the rear main seal.

First, the rear main seal is at the rear of your engine.  This can be confusing today because the rear of the engine isn’t always at the rear of your engine bay.  On a rear wheel or 4 wheel drive vehicle the engine is mounted with its front (the side with all the pulleys and belts) towards the front of the car.  With modern front wheel drive cars, and some all-wheel drive vehicles the engine can be mounted transversely in the vehicle.  This means that the front of the engine can be facing either the passenger or driver’s side of the vehicle.  So the “rear” in rear main seal refers to the seal’s location on your engine, and not necessarily relative to your vehicle.  The rear main seal is always on the opposite the side of your engine as the pulleys and belts.

Rear Main LeakSecond, the rear main seal is a seal for the main crank shaft bearings in your engine.  Since the crank shaft has the piston attached to it, the pulleys with all your accessories connected to it and the flywheel which connects to your transmission on it, it carries all the forces and power your engine creates.  Since the crank shaft has the toughest job, it gets the biggest and best bearings to make sure it can stand up to the work load.  These bearings are called the main bearings in your engine and carry the majority of the stresses on your crank shaft.  The rear main seal is just on the outside of the rear main bearing and it keeps the engine oil from leaking out where your crank shaft exits the engine.

The outside circumference of the rear main seal creates a seal between the engine block and sometimes the oil pan as well.  The inside of the rear main seal creates a seal on the crankshaft where it exits your engine to connect to the transmission.  As the crank shaft spins, it can wear down the rear main seal, especially if a low oil condition exists in the engine, or the vehicle sits for a long time between uses.

Because of its location in the engine, replacing a rear main seal includes at least removing the transmission from your vehicle, if not completely removing the engine as well.  Removing either the engine or the transmission from your vehicle is a difficult and time consuming job, usually making a rear main seal replacement a very costly project. This is why you hear so many horror stories about the unbelievable costs of fixing a leaking rear main seal.

The good news is that BlueDevil has created a way to seal your rear main seal leak easily and permanently without costly maintenance and long projects.  BlueDevil Rear Main Sealer is a specially formulated additive that you add directly to your engine oil.  BlueDevil Rear Main Sealer is not a petroleum distillate, powder, or hazardous chemical so it will not harm your engine in any way and can stay in your engine oil until your next oil change.  Once BlueDevil Rear Main Sealer is in your engine it will revitalize the old seals you have, restoring them to their original size, shape and flexibility permanently sealing your rear main seal leak – guaranteed!

BlueDevil Rear Main Sealer

Pick up a bottle of BlueDevil Rear Main Sealer at your favorite local auto parts stores like:

  • Pep Boys
  • CarQuest Auto Parts
  • Bennett Auto Supply
  • Prime Automotive Warehouse
  • NAPA
  • Advance Auto Parts
  • O’Reilly Auto Parts
  • AutoZone

You can also purchase BlueDevil Rear Main Sealer directly from BlueDevil.

Pictures courtesy of: www.lowridermagazine.com and www.precisionenginetech.com


33 responses to “Where is the Rear Main Seal?

    1. Where is the rear main seal at on a 1982 f250 auto with a 400 and do you have to remove the tryanny or the motor or both?

      1. Eric,

        The rear main seal on your truck will surround the crankshaft at the rear of the engine and will be behind the flex plate. If you have a 1 piece rear main seal (found on most new 351 motors) you will have to remove the transmission to replace the rear main seal. If your motor has a 2 piece rear main seal (found on older 351 and 460 motors) you should be able to replace it by simply removing the oil pan and the last main bearing cap.

        Thanks for your question!
        -BD Auto Pro

  1. I have a 2001 Jeep Cherokee with the 4.0 in-line six cylinder engine. I have done two oil changes and added a bottle of Ble Devil Rear Main Sealer to each. After driving the vehicle for longer periods it doesn’t seem to leak, but on short trips it still drips a little on the exhaust manifold (I can smell it) and leaves about a dime size spot overnight on the driveway. My question is would it do any good or better to use “two” bottles possibly to correct the problem? Thank You!

    1. You still only want to use the recommended amount, 1 bottle, with each application. We do not recommend adding 2 bottles at the same time; you would be better off simply retreating it with 1 bottle.

  2. I wanted to thank blue devil for there commitment and dedication to not only perfecting a great product, but for helping those in need. I have a family of 5 and only one working vehicle – a 2001 Toyota Sienna. With only one income, another vehicle is just not possible at the moment. My rear main seal went out in August 2014 and with almost 200,000 miles, I couldn’t find a mechanic willing to replace my rear main seal. Then, I heard about Blue Devils Rear Main Seal Stop Leak. After two weeks the leak stopped and the Toyota is doing fine. I’m so thankful that for just $15.00 my vehicle is ruuning just fine.


    Jason Cheek

  3. Any guidance with your product and a 1999 Toyota 4 Runner – V6?
    My concern is a non standard oil cooling system that utilizes coolant and can become blocked with sealers.

    1. Brad-

      The BlueDevil Rear Main Sealer does not thicken or harden so there is no risk at restricting flow or causing any type of clogging. The BlueDevil will react specifically with the rubber seals and gaskets by rejuvenating and slightly expanding them.

      Thank You!


  4. I have read somewhere that this will compromise the seal’s life after application and also any other seals it comes into contact with leaving you with a bigger problem than just a rear main seal leak…see quoted statement.
    “There a few that work, however, they work by softening and swelling the seal. The softened seal doesn’t last very long and the unfortunate side effect is that this happens to all your seals, leaving you with a bigger problem than you started with.”
    Is there any truth to that statement

    1. Ronnie,

      Thanks for your question. There is truth to this statement if you use products that contain petroleum distillates. Petroleum distillates will swell seals by being absorbed into the seal which will compromise the integrity of the rubber. BlueDevil products do not sue any petroleum distillates to recondition seals so our product creates a permanent seal.

      Thanks again for your question!
      -BD Auto Pro

  5. Hello, I strongly believe the real main seal is leaking from an early, rebuilt, 1950’s 8BA Ford Flathead engine. Have you had any experiences with this application? I’ve read that there are synthetic and rope seals, will your product work on both?

    1. Ken-

      The BlueDevil Rear Main Sealer would only be intended for the rubber seals. It would not have any effect on rope, cork or any other type of material that may have been used. If it is indeed a rubber seal, and you are not losing oil too quickly, you would be a good candidate for the product. You can expect to see results after about 100-200 miles of driving.

      Thank you!


  6. I have a 2010 Kia Soul. I’m at the shop now and they found a cam seal leak. What’s the difference between that and a main seal?

    1. Rebecca-

      Thank you for asking about your Kia Soul. The difference would be in the location of the seal. The cam seal is located by the timing chain cover and the rear main seal would be at the back end of the engine. Feel free to contact us at 888-863-0426 with any other questions.

      thank you!


  7. i have a 2008 Chevy Malibu and have a really bad oil leak coming straight off of the oil filter we have tightened the filter numerous times and it keeps coming loose . Could it have something to do with rear seal ?

    1. Jennifer-

      Thank you for asking about your Chevy Malibu. Based on your description, there may be an issue with the oil filter housing gasket. We recommend having the oil filter housing gasket replaced to stop the oil loss.

      Thank you!


    1. Ken-

      Based on your description, we recommend using the BlueDevil Oil Stop Leak (http://store.gobdp.com/oil-stop-leak-49499/) for your front engine seal leak. The BlueDevil Oil Stop Leak is a universal application, and will treat leaking oil pan gaskets, valve cover seals, rear main seals, etc. where as the Rear Main Sealer is specifically formulated for the rear main seal.

      Thank you!


  8. I have a leak on my rear main seal in my hyundai tucson, where do you check the oil level? is it same as the engine oil level?

    1. Andre-

      Thank you for asking about your Hyundai Tucson. You can check the oil level on the dipstick. Based on your description, we recommend using the BlueDevil Rear Main Sealer. You should expect to start seeing results after approximately 100-200 miles of driving.

      Thank you!


  9. Hi, I have 2004 Honda Odyssey. there is a possibility I might have a slow leak in my rear main seal. Is was recommended I get a second opinion on it. Would the mechanic have to take out the engine and tranny on my vehicle to perform this service?
    I just had my oil changed. Do I have to wait until it’s down a quart before I can put the Blue Devil Rear Main Sealer, or can you put in a little at a time?
    Appreciate your feedback.

    thanks, MD

    1. MD-

      Thank you for asking about your Honda Odyssey. The best way to prove that you’ve got a rear main seal leak is to check if the engine side of the flexplate or flywheel is oily. If the rear main seal is leaking on your engine it will drip oil onto the flexplate or flywheel and sling oil around the bellhousing. No, you would not have to wait until the oil was down before adding the BlueDevil Rear Main Sealer. If you are low on oil, add the product and top it off with oil to get it to the proper level.

      Thank you!


  10. I have a 2003 GMC Sierra with 240,000 miles. About a month ago I noticed a very small oil leak… 2 drops smaller than golf balls but larger than quarters… after the truck sat in the garage over night. I used Blue Devil Rear Main Sealer as prescribed (8 oz per 6 quarts of oil), drove the truck a couple days, and the leak stopped! I was very pleased. However, after 3 weeks and 800 miles with no apparent leaks, the oil drops have reappeared, the same as before.

    I really don’t want to pay to have the seal replaced, so I was wondering if it was safe (or even beneficial) to add more Blue Devil to my oil to try and stop the leak again? I have not changed the oil since the first time I added the product.

    Obviously I don’t want to do any damage to my engine, but would reapply Blue Devil if it was absolutely safe to do so.

    Thank you.

    1. Will-

      Thank you for asking about your GMC Sierra. Based on your description, we recommend using the BlueDevil Oil Stop Leak. 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.

      Thank you!


  11. I have a 2005 Dodge magnum that my son drove once and overheated it and ever since I cannot get it to start and stay on and at first I would fill the radiator reservoir and it was draining and then milky chocolate looking oil started spilling out on the ground I later discovered the old from the dip stick was also milk chocolate colored so I drained it and replaced it and it still won’t start it was leaking from the rear of the engine is this the rear main seal and would ur sealer work for this possibly

    1. Ashley-

      Thank you for asking about your Dodge Magnum. Based on your description, it sounds as though water/coolant is getting into the engine oil, creating the milky oil you are seeing. Unfortunately, water/coolant getting into the oil would be a tell-tale sign of a blown head gasket. If the oil is then spilling on the ground, you may be leaking an extreme amount of coolant, which is then overfilling the system and the excess is running out. If the vehicle was run for too long with water in the oil, it may have damaged the engine bearings to the point where the engine will no longer crank. This would mean that the engine needs to be replaced.

      Thank you!


    1. Holly-

      Thank you for asking about your Mazda. Replacing the rear main seal is a very labor intensive job, and will typically take about 8 hours to complete. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!


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