How to Tell If Your Rear Main Seal Is Leaking

mechanic looking for a leak, How to Tell if Your Rear Main Seal is leakingIf you’re wondering how to tell if your rear main seal is leaking, then your vehicle must be leaking something.  Before we get into the technical details of determining if you’ve got a rear main seal leak versus another type of oil leak, we need to be sure that it is indeed oil that your vehicle is leaking, not power steering fluid or transmission fluid or some other type of lubricant.  To be sure you’ve got an oil leak, try checking out our article on how to determine what your car is leaking.

Once you’re sure you’ve got an oil leak, we can help you figure out whether it is the rear main seal that is leaking or some other oil seal or gasket in your engine.

How to Tell If Your Rear Main Seal Is Leaking

  • Are there any higher oil leaks?
  • Are there drips from the bell housing?
  • Is the oil pan gasket leaking?
  • Is the flywheel or flexplate oily?

Since rear main seal leaks are uncommon on most vehicles it’s very possible that you’ve got another leak higher up on the motor that is dripping down and just looks like a rear main seal leak.  The most common leaks that can masquerade as a rear main seal leak is a valve cover gasket leak, intake manifold gasket leak or a distributor gasket leak.  If you find oil on your engine above the bellhousing, check for leaks at these locations.  If you find one, repair it, clean the engine and check for leaks again in a few hundred miles.

A rear main seal leak will cause oil to drip from the bottom of the bellhousing at the front of the transmission.  If you have drips coming from in front of the bellhousing, locate those leaks, stop them and clean the engine. After a few hundred miles you can check again for leaks to see if you still have any.

The most common leak that is confused as a rear main seal leak is an oil pan gasket leak at the rear of the engine.  The oil pan gasket is just below the rear main seal. An oil pan gasket is also usually much less expensive to replace so it’s important to check for leaks in your oil pan gasket before you jump to any conclusions.

The best way to prove that you’ve got a rear main seal leak is the 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. Most engines have an inspection cover in the bellhousing the allow you to check for this.  If you find oil on your flywheel or flexplate, use BlueDevil Rear Main Sealer to restore your rear main seal and stop your leak.
BlueDevil Rear Main Sealer


You can find BlueDevil Rear Main Sealer at any of our partnering local auto parts stores like:

  • 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 Distributor
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
  • Hovis Auto & Truck Supply stores
  • Salvo Auto Parts
  • Advantage Auto Stores
  • Genuine Auto Parts stores
  • Bond Auto Parts stores
  • Tidewater Fleet Supply
  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

Pictures Provided By:

leak_repair,jpg – By Welcomia – Licensed by Getty Images – Original Link

8 responses to “How to Tell If Your Rear Main Seal Is Leaking

  1. I notice my car has small leak after driving it but does not continue to leak when it just sits for days, does the rear main only leak when crankshaft is spinning or will it drip when car is not run also..although I did not get car on a lift but I can see it dripping down between bellhousing and flywheel inspection plate area.

    1. Al-

      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 specifically formulated for only a leaking rear main seal. 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. You should expect to start seeing results after approximately 100-200 miles of driving.

      Thank you!


  2. I have a duramax diesel leaking it holds 10 qts of oil I put 2 bottles of rear main seal still leaking can I add the oil stop leak on top of that

    1. John-

      Roughly how many miles have you driven since adding the Rear Main Sealer? Is the leak coming from the rear main seal or are you unsure? 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!


  3. Will injector cleaner damage what blue devil has already fixed I didn’t want to put injector cleaner in there until I asked. It’s been months since I put the blue devil on I just want to put the injector cleaner in now

    1. Hunter-

      Using the injector cleaner will not undo the seal that BlueDevil created. Once the product seals, it would be a permanent seal, so you should be good to go at this point.

      Thank you!


  4. Hi, I have a 2006 Impala. I had a small leak. Oil was on my oil pain, and when my car set, I had a few small oil spots on the passenger side, under the oil pan. The blue devil sealer, actually sealed whatever seal was worn because I no longer see oil spots under my car, on the passenger side. However, I still have oil leaking out. Oil, be leaking on my oil pan and my oil level will decrease over time, gradually. Now, does this mean I need to change the oil pan, along with oil pan gasket? Basically, is that the problem I am experiencing, now?

    1. Conrad-

      Thank you for asking about your Chevy Impala. Based on your description, it is possible you were dealing with multiple leaks. The fact that you noticed some kind of improvement is definitely a good sign. When was the BlueDevil added? Please contact our technical support line at 888-863-0426 so that we can get a little more information about the vehicle and be able to further assist you.

      Thank you!


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