By November 7, 2007 2 Comments Read More →

Rear Main Oil Seal Keeps Leaking

I have a Mazda 4 cylinder with manual transmission. I had an engine from a local savage yard put in to replace my bad motor. New seals and timing belt was done. Since having the engine installed, the first time I drove the car a distance, smoke came from under the car.

Lots of smoke. That night I noticed there was an oil spot in my driveway. I took the car back to the shop where the engine was installed. The mechanic replaced the rear main seal and gasket surrounding the main seal. I did not have any more oil leaks.

Now it is approximately a week later, I have been driving the car around town. No oil leaks. I drove to a neighboring city approximately 25 miles away. Used the highway. All gauges were fine. Ran air conditioner, Everything was fine.

My son noticed after I got back home and the car had set for a couple of hours an OIL SPOT. The spot was about the size of your hand not very deep,. I took the car back to the mechanic. Rear main seal is leaking. What is causing the rear main seal to leak? Take into consideration that there is no leaking when driving in town and leaking when I drive a long distance (Highway) .

My mechanic is puzzled also. He will be surfing the internet for answers to. (The mechanic does not want to fix the seal until he knows what is causing the seal to react the way it is.)

Thank you


Why hello there,

I would first TRIPLE check the entire engine AGAIN to make sure the oil leak is really from the rear main and not trickling down the engine from a valve cover gasket or some other seal or gasket. I would spray the engine down with CRC BrakeKleener which you can buy at any parts store…it is non flammable and dries instantly so you don’t have to use water.

Once the engine is completely clean and dry, then check for leaks starting at the top of the engine. They even sell an additive you can put in the oil that will glow green when used with a black light. This can be helpful in locating pesky leaks. The rear main seal usually gets blamed for leaking more times than not, and the problem seal is located higher up on the engine and running down the back and side of the motor dripping off the rear main area.

If you are positive the rear main is leaking again I would TRIPLE check the crankshaft to make sure the shaft is still perfectly round and balanced, does not have a bur or a lip cut into the shaft that the new seal can not seal up. I would also use a genuine MAZDA rear main seal if you have to do the job over again.


Austin Davis

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Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."
  • Austin Davis

    Hi TC,

    Do you think this jerking you are feeling is from the engine, like an engine miss or is it more of a suspension type of problem under the vehicle? Check engine light on?, any other engine related issues happening?

    Any tire wear, or front end issues like pulling to one side that might be related?

  • Tracey Copeland

    Hi, my name is TC. Im having a problem with my 2001 dodge seems to jerck slightly when im driving slowly with my foot on the peddle .And lately the jercking is getting worse I went over a.dip and the truck jerked a little harder .Please help I am disabled and cant afford another vehicle right now please give feedback on what could be the problem.