Will A Rear Main Seal Leak When Not Running

When it comes to car maintenance, understanding how different parts operate can save you a lot of headaches down the road. One common concern among car owners is whether a rear main seal will leak when the vehicle is not running. As a passionate car enthusiast, I’ve delved into this topic to provide you with a comprehensive understanding of rear main seals and their potential for leakage.

Understanding the Rear Main Seal

The rear main seal is a critical component of a vehicle’s engine, located at the back of the crankshaft. Its primary function is to prevent oil from leaking out of the engine and onto the ground. A worn-out or damaged rear main seal can lead to oil leaks, resulting in potential damage to the engine and environment.

Will it Leak When Not Running?

It’s normal for a rear main seal to experience some degree of seepage even when a vehicle is not running. This seepage is often due to the residual oil left on the crankshaft after the engine is turned off. However, if the seepage progresses to a consistent drip or puddle underneath the vehicle when it’s not in use, it’s a clear indication of a leaking rear main seal. This leakage can be attributed to wear and tear, heat cycling, or prolonged periods of inactivity.

Causes of Leakage

Several factors can contribute to rear main seal leakage when a vehicle is not running. Continuous exposure to high temperatures, such as those experienced in heavy traffic or during long drives, can result in the degradation of the rear main seal material over time. Additionally, prolonged periods of inactivity can lead to the drying out and hardening of the seal, increasing the likelihood of leaks.

Preventive Measures

Regular maintenance and inspection are essential for preventing rear main seal leaks. Keeping the engine well-lubricated with high-quality oil and ensuring it operates at optimal temperatures can help prolong the lifespan of the rear main seal. Additionally, driving the vehicle regularly can prevent the seal from drying out and losing its flexibility. If you notice any signs of leakage, addressing the issue promptly can prevent further damage and costly repairs.


It’s important to be mindful of rear main seal leakage, even when your vehicle is not running. Understanding the factors that contribute to such leaks and taking preventive measures can help maintain the integrity of your vehicle’s engine. Regular maintenance, prompt repairs, and keeping a close eye on any signs of leakage are crucial in ensuring the longevity of your rear main seal and the overall health of your vehicle.