Why Do I Have a Rear Main Seal Leak?

You may have a rear main seal leak for a variety of reasons. First we will take some time talking through what rear main seals are designed to do, then we will look at the causes for a leak. The rear main seal in your vehicle holds the engine oil in the oil pan while allowing the crank shaft to exit the engine block. The bearings that support the crank shaft are called the main bearings in your engine, so the rear main seal is a seal just outside of the last main bearing at the rear of your engine. The rear of the engine is the side opposite, all of the pulleys and accessories like the power steering pump or alternator. Your rear main seal may be one or two pieces and is likely made out of a special type of rubber or silicone that is designed to handle the temperatures and chemicals in your engine oil. Ideally the outside of the rear main seal will press tightly against the engine block and/or oil pan not allowing engine oil to leak out and the inside of the rear main seal will slide over the crank shaft keeping oil from slipping past it as the shaft spins.

Your rear main seal may develop a leak for a variety of reasons:

Old Age
Lack of use
Outside elements
Corrosion
Extreme operating conditions

Anytime you have a surface rubbing on another, no matter how much lubricant you use or how smooth the surfaces are, overtime one will wear down. In the case of your rear main seal, rubber is softer than metal so the rubber seal will wear down first causing a leak.

A lack of use is one of the silent killers of the seals and gaskets in the engine of your vehicle. Regularly driving your vehicle will keep the oil circulating though the engine and this will help keep all the seals soft and conditioned. Without a regular oil bath, your rear main seal can become dry and hard causing it to not seal properly around the rotating crank shaft. Also, when your vehicle is not running, the crank shaft will sit down on the bearing surfaces they ride in. This very small movement stretches the rear main seal opening just slightly, but if left for a long time, can permanently deform your rear main seal causing a leak around the crank shaft.

Most vehicles have inspection covers or skid plates to keep the elements like water, sand and dirt away from the outside of the rear main seal, but over time, some outside elements can make their way to the seal. Things like sand, salt or road grime can cause premature failure of your rear main seal from the outside in.

There are many reasons you should regularly change your engine oil. Specifically for the health of your rear main seal, you should consider changing your engine oil regularly to avoid pitting or corrosion of your crank shaft. Old oil can become acidic over time as it absorbs water and goes through the heating and cooling cycle of a running motor. This acidic oil sits between the rear main seal and the crank shaft lubricating it, but also corroding and possibly pitting your crank shaft. This corrosion will create a rough surface which will quickly wear out your rear main seal, causing a leak.

Extreme operating conditions like extraordinarily high heat or foreign chemicals can also cause rear main seal failure. High heat can cause seals to get brittle or hard and chemicals can cause reactions with the materials some seals are made from. For example, try leaving a pair of rubber gloves in transmission fluid overnight and they will be brittle and hard in the morning. Be careful to operate your vehicle only with proper coolant temperatures and never put abnormal chemicals in your engine oil.

Some oil leaks can easily be stopped with our Oil Stop Leak, however, if you do find yourself with a rear main leak you can fix it using BlueDevil Rear Main Sealer. BlueDevil Rear Main Sealer will restore your worn, dried, cracked or distorted rear main seal back to its originally shape, size and flexibility sealing your leak and returning your car to reliable operation. We’re so confident in our Rear Main Sealer that it is guaranteed to permanently seal your leak!