How Bad is a Rear Main Seal Leak?

rear main seal leakMaybe you’ve gotten the news that your vehicle has a leaking rear main seal.  Or perhaps you’ve started to notice oil dripping from the back of your oil pan and have wondered if you may have a rear main seal leak.  No mater why you’re asking “How bad is a rear main seal leak”, the answer unfortunately is, it’s bad.

A leaking rear main seal leak can cause a lot of problems with your vehicle.  The rear main seal is the seal that goes around your crankshaft at the rear of the engine.  The crankshaft in your engine is held to the bottom of your engine block using main caps at each of the bearings.  The oil pan is then bolted on over that, and a seal has to be placed over the crankshaft in between the block and the oil pan.  This seal helps keep dust and dirt out of your engine and helps hold the oil inside the oil pan.

The reason a rear main seal leak can be so dangerous is due to the nature of the seal.  The inside of your rear main seal is in contact with your crankshaft as it is spinning around thousands of times every minute.  This seal is also right next to one of the main bearings in your engine which needs to be constantly lubricated by oil.  The constant bath of oil combined with the spinning motion of the crankshaft will cause a rear main seal leak to allow a significant amount of oil to leak from your engine as its running.  The gaskets in your engine can also cause leaks, but since there is no relative motion there, the leaks or often slow and more of a weeping or seeping than a drip or stream.

Also, once your rear main seal starts to fail, the rotation of your crank shaft can cause the problem to go from bad to worse extremely quickly.  Rear main seals usually start to leak due to a worn surface or a small crack and the constant stress of rubbing on the spinning crank shaft can make worn surfaces or cracks get much worse very quickly.

rear main seal leakA rear main seal leak can cause problems for your engine quickly because it can allow such a significant amount of oil to leak out very quickly.  Most engine oil leaks will lower your over level to a dangerous point over a matter of weeks or even months.  A rear main seal leak, on the other hand can cause your engine oil level to drop to dangerous levels in a matter of minutes, or perhaps even more quickly.  Your vehicle is equipped with a low oil pressure light which can help alert you to a problem, but if your engine has low oil pressure it may already be too late and damage already be done.

A low oil level in your engine is one of the quickest ways to cause permanent engine damage.  A low oil level will uncover your oil pump pick up screen causing oil to stop flowing through your motor leaving your cam shaft, bearings, and valves to move without lubrication.  Also, a low oil level means your crank shaft is no longer splashing in the oil which helps cool and lubricate your main bearings, rods and piston rings.  Even at normal driving speeds this lack of oil can cause permanent damage to happen in a mater of seconds.

BlueDevil Rear Main Sealer

If you’ve discovered a rear main seal leak in your vehicle, seal the leak today before it’s too late.  Head to your local auto parts stores and pick up BlueDevil Rear Main Sealer.  Simply add BlueDevil Rear Main Sealer to your vehicle’s engine oil and your rear main seal leak will be stopped as your drive your vehicle.  You can pick up 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 Distributer
  • DYK Automotive

You can also purchase BlueDevil Rear Main Sealer Directly from BlueDevil’s website here: Rear Main Sealer

Pictures provided by:

Oil Leak – Bryn Pinzgauer – Licensed by Creative Commons Share Alike 3.0 – Original Link
R
ear Main Seal – Andrew Davldoff in “Cars” – Licensed by Creative Commons Share Alike 3.0 – Original Link

100 responses to “How Bad is a Rear Main Seal Leak?

  1. If your main sealer is poured in at the oil change, can it be left in for 3500 miles or does it need to drained when the leak stops? Also, is there a dange of stopping up internal block oil passages?

    1. Sir-

      It can be left in for the full 3500 miles (life of the oil). The BlueDevil Rear Main Sealer does not harden or thicken in any way so there is no possibility of clogging or any type of flow restriction when using this product.

      Thank You!

      -BDP

      1. Vee-

        Thank you for asking about your Infinity QX4. Yes, you are fine to add the product to your existing oil. Typically, you will stat to see improvement after about 100-200 miles of driving. The product can stay in the oil for the life of the oil, so it does not need to be changed out immediately after proper results are achieved.

        Thank you!

        -BDP

    2. Hello I added rear main sealer in my 96 Dodge Ram 1500 only noticed small leak couple drops on drive way maybe for past few months leaked maybe half quart oil but blue devil in and still leaking?

      1. Micki-

        Thank you for asking about your Dodge Ram 1500. Please contact our technical support line at 888-863-0426 so that we can get a better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

        Thank you!

        -BDP

  2. My 1972 challenger takes 5 quarts of oil at every oil change. If I add your rear sealer at
    that time, can I still add the 5 quarts of oil, or will it be over filled ?

    1. Tony-

      It would not be necessary to use both products at the same time. If you have multiple leaks then you will only need to add 1 bottle of the BlueDevil Oil Stop Leak; it would address the rear main leak as well.

      Thanks!

      -BDP

  3. 99 eclipes with a bad rear main seal. ill be doing the work myself. but i need to know. is there any quick fix i can do. so i can get it to the shop i need to work on it at. the shop is around 45 mins away from my place. could i drive it with a quick fix till i get it to the shop, or just get it towed?

    1. Chris-

      We do manufacture a product called the BlueDevil Rear Main Sealer but if you are losing oil so quickly that you are unable to drive the vehicle then the leak is too large for what BlueDevil is intended to fix.

      Feel free to contact our tech support team at 888-863-0426 with any further questions.

      Thank You!

      -BDP

  4. I have a 1992 honda accord lx, it’s leaking I think from the camshaft seal, what is the strongest oil stop leak do you have, this seems to be the only issue with my car, having to keep oil in it.

  5. I have 03 4.3l Chevrolet. I added one bottle of Rear seal leak fix from you guys. It slowed a bit but still leaks. I really dont want to drop the transmission to swap the seal just yet. Will it hurt anything to add another bottle just to see if it works?

    1. Jeff-

      How many miles have you driven since the BlueDevil Rear Main Sealer was added?

      Feel free to contact us at 888-863-0426 to discuss your vehicle further.

      Thank You!

      -BDP

        1. Justin-

          We would like to discuss the leak and your vehicle in a little more detail. Please contact our tech support team at 888-863-0426; we would be happy to help you out!

          -BDP

          1. I have a e 350 van 1999 hade a rear main seal put in cost 1000.oo it still leaks put in 3 blue devil rear main sealer. still leake?

          2. Leonard-

            How many miles have you driven since BlueDevil Rear Main Sealer was added? It can take up to 200 miles of driving before you see the full results of the product.

            Thank you!

            -BDP

    1. Garry-

      We do not currently have any distributors in Australia but the product can be purchased direct through our website (www.gobdp.com) and shipped to your residence. The website will automatically calculate the shipping cost after you enter your mailing address.

      Thank You!

      -BDP

  6. I have an 02 acura rl that has oil leaks from the rear main seal as the mechanics said , can I put the blue devil rear main sealer with the existing oil I have?

  7. I just want to know, if I have replaced the seal, what could cause that there is still a leak,because it’s stressing me realy out.please help

    1. Earl-

      It may be that the leak is coming from elsewhere, ie. oil pan gasket, valve cover seal, etc. We would recommend using the BlueDevil Oil Stop Leak, found here: http://store.gobdp.com/oil-stop-leak-49499/ . The Oil Stop Leak is a universal application and would be able to seal leaks coming from the rubber seals or gaskets in the system. Feel free to contact our technical support line at 888-863-0426 with any questions.

      Thank you!

      -BDP

  8. I added the stop leave to my engine oil and run it for the recommended 1-2 hours. As I drive I was getting a lot of smoke coming from the car is this normal or another problem??

    1. Rich,

      The smoke is not normal for using oil stop leak. If the smoke is coming from your tailpipe, it is an indication that you’ve got a bigger problem like too much oil or internal damage to your engine. If the smoke is coming from your engine bay, it is an indication that you have a bigger leak and should consider replacing the seal or gasket to avoid a fire hazard.

      Thanks again for your question!
      -BD Auto Pro

      1. Kyle-

        Yes, that is possible. If you are not 100% sure where the leak is coming from, we recommend using the BlueDevil Oil Stop Leak http://store.gobdp.com/oil-stop-leak-49499/. The BlueDevil Oil Stop Leak is a universal application and would treat leaking oil pan gaskets, valve cover seal, rear main seal, etc. Feel free to contact our technical support line at 888-863-0426 with any other questions.

        Thank you!

        -BDP

  9. I have a 88 corvette,bought in April with 49000 miles.Today I found the rear main is leaking.Will your product stop the leak and should I drive it before I store it in Nov? Thank you. Larry aka sick to my stomach.

  10. I have an 88 f150 with the 302. It looses about a quart of oil for every 20 miles i drive it would blue devil be enough or is the leak too severe?

  11. I have a 1991 jeep Cherokee Laredo that is leaking from the rear seal and the front seal, is the rear main seal is enough for this problem or there is another product that i can use

    best regards
    Jose Fuentes

    1. Jose-

      Based on your description, we would recommend using the BlueDevil Oil Stop Leak. The Oil Stop Leak is a universal application so it would treat an oil pan gasket, valve cover seal, rear main seal, etc. Where as the Rear Main Sealer is specifically formulated for the rear main seal, so it would really only be able to seal leaks coming from this area. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  12. I was told having a rear main seal leaking bad. I put in a can and drove over 300 and seems to have slowed down a lot. Seeing a small spot..should I continue to drive and see if stops or drain and refill oil and then add another can to see if it stops completely..what do you recommend.

    d

  13. I have a 2013 ford focus with 28,700 miles; ford announced an extended warranty on these (and other model years)
    ‘Transmission clutch shudder/trans. input shaft seal’ – I just had an oil change (not at the dealer) and a comment
    on the bottom sheet was ‘rear main seal does leak’; I’m thinking this is what ford was talking about (extended warr);
    The drives fine and I haven’t noticed any leak under my car (haven’t looked closely) ; I made an appt. for service
    on the 29th of Dec.; should I wait that long or get it looked at sooner? (I guess that was the earliest possible day
    for the appt) I told the service person about the leak……..

    1. Scott,

      Thanks for your question about your Ford Focus. Based on your and the mechanic’s description of the problem you should be just fine to wait until the 29th to have your car looked at. Unless you’re seeing puddles of oil under your car after parking it your rear main seal isn’t leaking bad enough to cause any immediate problems. Hopefully Ford will honor their extended warranty and get your problem fixed quickly!

      Thanks again for your question!
      -BD Auto Pro

  14. 97 Honda accord se. Has an oil leak coming from the back of the engine somewhere causing the oil burning smell.. Not sure of where its coming from. New head gaskets, valve cover gasket, distributor o-ring, oil pressure switch ect… I think it could be the rear main seal being it wasn’t changed when I had the transmission swapped. What would you suggest using? Rear main sealer or oil stop leak?

    Thanks. Nick

    1. Nick-

      Thank you for asking about your Honda Accord. The BlueDevil Oil Stop Leak is the universal application and will work for oil pan leaks, rear main leaks, valve seal leaks, transmission leaks, power steering leaks, etc. Whereas the Rear Main Sealer is specifically formulated for the rear main seal. If you are not sure where the vehicle is leaking or there seem to be multiple leaks, we would recommend using BlueDevil Oil Stop Leak.

      Thank you!

      -BDP

  15. I have just discovered a leak under my car, while replacing a radiator fan. My dad says it looks like the rear main seal. Without knowing, do i use your RMS leak stopper or go straight to Blue Devil Oil stop? I dont know how long its been leaking, saw a little bit a week ago, no low oil light, but i am at the min level now. Also no noticeable puddles under my car and didnt leak while i was under it. Just wet.

    1. Mike-

      Thank you for asking about your VW Rabbit. Based on your description, we would recommend using the BlueDevil Oil Stop Leak. The BlueDevil Oil Stop Leak is the universal application and will work for oil pan leaks, rear main leaks, valve seal leaks, transmission leaks, power steering leaks, etc. Whereas the Rear Main Sealer is specifically formulated for the rear main seal. If you are not sure where the vehicle is leaking or there seem to be multiple leaks, the Oil Stop Leak would be the best place to start.

      Thank you!

      -BDP

  16. It appears that the rear main sealer is superior to the oil stop leak when the leak is specifically the rear main seal. If not why do you make two products that equally fix a rear main seal leak.

    1. Dave-

      The Oil Stop Leak is the universal application and will work for oil pan leaks, rear main leaks, valve seal leaks, transmission leaks, power steering leaks, etc. Whereas the Rear Main Sealer is specifically formulated for the rear main seal. If you are not sure where the vehicle is leaking or there seem to be multiple leaks, we would recommend using the Oil Stop Leak. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  17. I have 88 Ford f-150 5.0 302 & I just bought ur rear main seal repair cause I’m losing about a little under a half of Cort of oil maybe not that much but longer it sits its alit more, but my question is if I put this in my oil will it leak out with the oil & how long does it take to fix it.

    1. Robert-

      We recommend adding one 8 ounce bottle of BlueDevil Rear Main Sealer. You can expect to start seeing results after about 100 miles of driving.

      We also recommend that you change your transmission fluid and filter; be sure to fill it to the proper level. The rough shifting may be due to old/dirty transmission fluid. If the “jumping” continues after doing so then your best bet may be to have it looked at by a transmission specialist.

      Thanks!

      -BDP

  18. Would this work for 475 hp Cummins isx diesel engine and is it available in Canada? Front accessory seal leaking and oil pan.

    1. Mike-

      Based on your description, we would recommend using the BlueDevil Oil Stop Leak, found here: http://store.gobdp.com/oil-stop-leak-49499/ . The Oil Stop Leak is a universal application and would treat leaks coming from the oil pan gasket, rear main seal, etc. Whereas the Rear Main Sealer is specifically formulated for the rear main seal. We do not currently have any retailers in Canada, however, the product is available for sale on our website and we do ship Internationally.

      Thank you!

      -BDP

    1. Nelly-

      You will not have to replace the rear main seal any time after using BlueDevil Rear Main Sealer. Once the leak has stopped, the seal will have the life of a new seal.

      Thank you!

      -BDP

    1. Jr-

      A leak should not develop when the vehicle has been driven under 10,000 miles. We recommend checking with the dealership to replace the seal as the vehicle should still be under warranty.

      Thank you!

      -BDP

  19. Hi I have noticed in the last week that my rear main seal is leaking. I have a Straight truck Freithliner Business Class 2007 How much do I need to add to help stop the leak one or two bottles? Thanks

  20. Hi,
    I have 96′ Toyota Celica GT, auto/trans, 145,000 miles.
    I have a couple of issues with my motor and I was hopping that I could fix my R.M.S. at the same time while i’m using a Lucas “Stop Smoke” additive?

    Any suggestions would be greatly appreciated!

    Thx.

    Steve B.

    1. Steve-

      Thank you for asking about your Toyota Celica GT. Yes, you can add the BlueDevil Rear Main Sealer to your current engine oil, as it would be compatible with the Lucas additive you are using. You should expect to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

  21. I have an 09 VW CC 2.0L TSI 6-speep turbo in the shop now and the dealer said the rear main seal is leaking a little. If I add the BlueDevil Rear Main Sealer with this cause any harm to a turbo-charged stratified injection engine?

    1. Kirk-

      Thank you for your interest in the BlueDevil Rear Main Sealer. The product does not harden or thicken in any way, so it would not have any adverse affects on your engine. You should expect to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

      1. Marquis-

        Overall, BlueDevil Rear Main Sealer carries a success rate of over 90%. As long as you are not dealing with a severe oil leak you should have no problem sealing it using BlueDevil Rear Main Sealer.

        Thank you!

        -BDP

    1. Lukas-

      For proper results, you would need to drive the vehicle in order for the product to seal. Typically, you should start to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

  22. i have a 86 camaro with the 2.8 the underneath is coated with oil and i lose about a quart every week to two weeks

    1. William-

      Thank you for asking about your Camaro. If you are positive the leak is coming from the rear main seal, then the BlueDevil Rear Main Sealer would be able to treat the leak. If you are not completely sure or if you have multiple leaks, I would recommend using the BlueDevil Oil Stop Leak. The Oil Stop Leak is a universal application and would treat a leaking oil pan gasket, valve cover seal, rear main seal, etc. where as the Rear Main Sealer is specifically formulated for the rear main seal. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  23. I have a 6.0 Cadillac motor with a hundred and twenty thousand miles a small leak on the main seal but it does cause me to put a quart of oil every 3 months should I change my oil now what fresh oil in it is that okay after using Blue Devil

    1. Frank-

      Yes, you may add BlueDevil Rear Main Sealer on a fresh oil change. The product can be left in for the life of the oil. Once it has been added you can expect to start seeing results after about 100 miles of driving.

      Thank you!

      -BDP

  24. I have a 1981 corvette that is leaking oil from the rear main seal.will blue devil main seal sealer take care of this problem ? Also do you have to use it every time you change the oil?

    1. Bobby-

      Thank you for asking about your Corvette. The BlueDevil Rear Main Sealer is compatible in your vehicle. As long as you are not losing oil too quickly, you would be a good candidate for the product. Typically, you should expect to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

  25. I have a Hyundai/Kia Epsilon G4HE(1.0L) engine which is notorious for developing rear main seal leaks. While mine is still leak free, I was wondering if adding a can of BlueDevil Rear Main Sealer as a preventative measure would be effective or not in stopping or prolonging a leak from developing?

    1. Yes, you may use BlueDevil Rear Main Sealer as a preventative measure. The product will rejuvenate and recondition the rubber seals & gaskets within your fluid oil system.

      Thank you!

      -BDP

  26. One more question, on my 6.0 diesel ford engine should I use 1 treatment of blue devil rear main seal or 2 because of the amount of oil needed per oil change?

  27. I have serviced my car today. The mechanic said there is rear main oil seal leak in the car. But I have not found any oil coming out in the rear side of the car. However, I find very small amount of oil at front of the car. What does this mean? He also said there is leak in engine oil pan. Is it really dangerous?

    1. Pasha-

      Thank you for your question. Based on your description, it sounds like you are experiencing multiple leaks. We recommend using the BlueDevil Oil Stop leak to treat the leaks in your vehicle. The Oil Stop Leak is a universal application and would treat leaks coming from the oil pan gasket, valve cover seal, rear main seal, etc. You should expect to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

  28. I have a 1962 Ford Falcon with 170ci 6 cylinder. I have replaced the rear seal ( two piece seal) with a rubber seal…actually changed it three times. Each time it seems to take thirty minutes…last time it took one hour before it starts a very slow drip. It is definantly coming from the rear main seal. Will Blue Devil take care of this issue?

    1. John-

      Thank you for asking about your Ford Falcon. As long as you are not losing oil too quickly, you would be a good candidate for the BlueDevil Rear Main Sealer. Typically, you will start to see results after about 100-200 miles of driving.

      Thank you!

      -BDP

  29. Had my 09 Escape in for an oil change last week. Using high mileage oil as I’m currently at 328,000km. They informed me that they believe I have a rear main seal leak and there was oil around the oil pan. I found this page after searching another issue. I keep reading your product doesn’t harden. If I bought the BD Oil Stop Leak, how does it repair the seals?
    I don’t have any puddles or marks on the ground beneath the car so I’m guessing the leak is very slow.
    Would using this product be ok with high mileage oil?
    How does it seal without going hard? I’d hate to use it and cause other issues.
    Thanks

    1. Rob-

      The BlueDevil Oil Stop Leak does not harden or thicken in any way, so it would not have any adverse affects on the engine. The product seals leaks by revitalizing and reconditioning the rubbers in the system, and will expand them, or slightly swell them back to their original state. The product is also compatible with synthetic oil. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  30. I have a 1999 Dodge Stratus with 157,000 miles. I have always had the proper maintenance done on time. I have always had an oil spot on my garage floor but noticed the last couple of months that it was getting larger. I took my car to my local mechanic who I have used for many years. He told me that it was a real main seal. I cannot get the work done for a couple of weeks due to personal circumstances and was told it was okay to drive it. He assured me the leak has been occurring for a period of time and not all at once. Will the Blue Devil Rear Sealer work in my car and hopefully stop the leak? Or is this a band-aid approach and the real main seal will have to be replaced anyway?

    1. Linda-

      Thank you for asking about your Dodge Stratus. Based on your description, you would be a great candidate for the BlueDevil Rear Main Sealer. Once the product seals, it would be a permanent seal. Typically, you would start to see results after about 100-200 miles of driving. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  31. Hi there, I just used the blue devil rear main sealer in my truck yesterday. After driving it for 30 minutes and letting it sit over night, I noticed a fluid mark under my truck the same size of the oil marks I was getting from the oil leak, but the fluid was 90℅ blue devil rear main sealer and maybe 10℅ oil. Is it normal for the sealer to leak out without mixing with the oil, or does it not mix together just like water and oil?

    1. Kevin-

      Yes, it is normal to see the product separate from the engine oil when some has leaked out. The product works by reconditioning and rejuvenating the leaking rubber seal or gasket. Expect to start seeing results after about 100 miles of driving; it is still too early to know whether or not the product is going to work after a 30 minute drive.

      Thank you!

      -BDP

  32. My mechanic found a rear main seal leak in my 2002 Acura MDX with 160k miles. There is no oil leaking where we park it overnight, just in the pan under the car. I found your Rear Main Sealer online, and asked my mechanic about it. He said liquid sealers that patch the seals can cause adverse effects on other parts of the engine that you do not want to be sealed, like valves. He said it’s only recommended for older cars to keep them going for longer.

    What are all of the possible side effects of using Rear Main Sealer? Thanks

    1. Jamie-

      BlueDevil Rear Main Sealer does not harden or thicken to stop leaks, therefore there is no risk in using it in your steering unit. It is 100% safe and compatible to use in your Acura. BlueDevil works by slightly expanding the rubber seal or gasket and reconditioning it to bring it back to its original size and condition.

      Thank you!

      -BDP

  33. I have a 2003 Acura MDX and my mechanic said I have an Oil pan leak and he will have to drop the pan which will cost over $800 . Will the blue devil oil stop leak work or will there be side effects if I use it

  34. I have a 2006 Mercedes cls 500 which has a slight leak in my rear main seal. Will this product have any adverse reaction on this engine?

    1. Carantino-

      Thank you for asking about our Mercedes cls 500. The BlueDevil Rear Main Sealer will not harden or thicken in any way, so no, it would not have any adverse affects on the engine. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  35. I own a 2003 Chevy Cavalier. I was told that I have a rear main seal leaking. I put in BlueDevil Rear Main Sealer yet it didn’t stop the leak .Would I be able to add the Bluedevil Oil Stop leak just in case the diagnosis was incorrect or I may have several leaks from different places or would the Oil Stop leak interfere with the Rear Main Sealer ? Thanks Cile

    1. Cecile-

      You should not have to add both products to stop your rear main leak. Keep in mind it usually takes at least 100 miles of driving before you will start to see results after BlueDevil Rear Main Sealer is added. If you haven’t driven more than 200 miles with the product in the system then it may be too early to tell as to whether or not the product is going to work.

      Feel free to contact us at 888-863-0426 with any questions.

      Thank you!

      -BDP

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