What Is A Rear Main Seal?

By Adrianna | August 12, 2014

Some people never make an attempt to understand how their car works. Poker prodigy Stu Ungar reportedly bought a BMW with his World Series of Poker winnings and never once changed the oil. When the car ceased up, he had no idea why. For many car owners, learning about your car and how it works is a lifelong journey. Having gone through my fair share of costly trials and tribulations with vehicles (only being saved later by an extended warranty on my Ford Explorer – thanks Warrick!).

Anyhow, one issue I ran into on an old beater was a leaking rear main seal. These can be bad news if they happen to your car. But before I get into what happens, I’ll fill you in on what a rear main seal is so you’re not living in the sea of ignorance I once inhabited.

rear main sealHere is a rear main seal

The rear main seal’s job is to seal the back of the car’s crankshaft. This is an extremely important job, as it must handle these responsibilities:

1. Keeping the oil in your engine (if this isn’t happening, welcome to Stu Ungar land)

2. Handle the crankshaft’s rotation and heat expansion (no small feat, either)

As you might imagine, if this is leaking, your car can be in big trouble. No oil means no go. ┬áThe problem when these start to leak, though, is that they’re usually in a nearly impossible place to get to in your vehicle. So, if you do have a leak, the likelihood of a cheap, easy repair is next to nothing. If your seal’s going, someone’s going to have to basically take your engine apart to get to it and make a fix. On an older car this might not even be worth it. Though, as this good article on diagnosing a leak points out, there are some products out there that might be able to fix some smaller leaks for free.

Looking for more info on rear main seals? Check out these video resources:


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