Replacing a Rear Main Seal

Rear main seal replacementReplacing the rear main seal can be an insurmountable job for a weekend mechanic, and can even be a challenge for a seasoned professional.  The rear main seal is on the rear of the engine and seals the point where the crankshaft extends out of the engine block.

Most of the time, you will discover a rear main seal leak by finding oil drips on the ground since you can’t, or at least should be able to see the rear main seal by looking up under your car.  The rear main seal is sandwiched vertically between your engine block and oil pan, and is in the engine block just inboard of the flywheel.  Many times if it is leaking you will find drips on your back of your oil pan or on the front transmission bell housing.  First, but sure to check that the leak isn’t up higher and just dripping down the back of your motor.  A leaking valve cover gasket or valley pan gasket can easily be confused for a rear main seal leak if you don’t check for a higher leak point.

Replacing a Rear Main SealIf you’ve searched around with your mechanic’s mirror and flashlight and have determined you don’t have a valve cover of valley pan leak, you may have a rear main seal leak.  Even though the rear main seal is a relatively inexpensive and simple oil seal, it’s in a very difficult place to get to service.  To remove the rear main seal, you must remove the transmission from the engine, remove the flywheel from the crank shaft, removed the oil pan and in most motors removed the pistons and crank shaft as well.  Unless you want to get really creative and uncomfortable, this would also include removing the motor from the vehicle as well.  To re install the pistons and crank shaft in an engine requires a good understanding of how a motor works to make sure the correct timing and torque settings are used.  This sort of job should really be left to professionals.

The majority of the cost for a rear main seal replacement is in the labor involved to remove the engine and transmission from your vehicle.  Often times once you’ve paid for that kind of labor, you could have afforded to replace the entire motor, or even your entire car.

When trying to decide if performing an expensive maintenance item on your vehicle is worth it, it helps to understand what your vehicle is worth both in its unrepaired state and what it would be worth after it has been repaired.  To determine the unrepaired value try searching local auto listings for other “mechanic specials” or cars that are in need of repair, asking local garages and repair shops, or check with your local salvage or scrap yard on their rates for whole vehicles.  Another option to consider is donating your car to charities like the Kidney Cars Program ( or Cars for Veterans (  The tax write off may be worth more than you think!  For the repaired value you can use Kelly Blue Book (, Edmonds ( or the National Auto Dealers Association (  I like to check the value on all three sites and find an average.  If the cost to repair your vehicle is more than the difference in the unrepaired and repaired values, you may consider looking for a new vehicle and selling your current vehicle as-is.

The other option is to try and get a second opinion on your leaking rear main seal to see if there is a way to fix the problem without the high price tag.  The guaranteed permanent solution is to add 1 8oz. Bottle of BlueDevil Rear Main Sealer to up to 8 quarts of engine oil.  BlueDevil Rear Main Sealer will mix with your engine oil and recondition the current rear main seal in your car or truck.  BlueDevil Products will not harm any components in your engine and can stay in the engine oil until your next regular oil change.

BlueDevil Rear Main Sealer

You read more about BlueDevil Rear Main Sealer here: Rear Main Sealer

You can also purchase BlueDevil Products at any of our partnering retailers:

  • Bennett Auto Supply
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