Where is the Rear Main Seal?

Having a problem with the rear main seal in your vehicle can be a scary thing, mostly because many of us don’t entirely know what that seal is or does. We’ve only heard horror stories about friends who had great reliable vehicles that developed a rear main seal leak and suddenly their car was only fit for a junk yard. Here at BlueDevil we’re hoping to change that myth.

The rear main seal is a seal in your engine that is very important and usually difficult to reach. If you pop your hood and start looking around for the rear main seal, you aren’t going to have much luck seeing it. It is buried deep, usually under a lot of protective covers, wires, hoses and unfortunately, the bell housing of your transmission. Let’s first break down the name to see what we can learn about the rear main seal.

First, the rear main seal is at the rear of your engine. This can be confusing today because the rear of the engine isn’t always at the rear of your engine bay. On a rear wheel or 4 wheel drive vehicle the engine is mounted with its front (the side with all the pulleys and belts) towards the front of the car. With modern front wheel drive cars, and some all-wheel drive vehicles the engine can be mounted transversely in the vehicle. This means that the front of the engine can be facing either the passenger or driver’s side of the vehicle. So the “rear” in rear main seal refers to the seal’s location on your engine, and not necessarily relative to your vehicle. The rear main seal is always on the opposite the side of your engine as the pulleys and belts.

Second, the rear main seal is a seal for the main crank shaft bearings in your engine. Since the crank shaft has the piston attached to it, the pulleys with all your accessories connected to it and the flywheel which connects to your transmission on it, it carries all the forces and power your engine creates. Since the crank shaft has the toughest job, it gets the biggest and best bearings to make sure it can stand up to the work load. These bearings are called the main bearings in your engine and carry the majority of the stresses on your crank shaft. The rear main seal is just on the outside of the rear main bearing and it keeps the engine oil from leaking out where your crank shaft exits the engine.

The outside circumference of the rear main seal creates a seal between the engine block and sometimes the oil pan as well. The inside of the rear main seal creates a seal on the crankshaft where it exits your engine to connect to the transmission. As the crank shaft spins, it can wear down the rear main seal, especially if a low oil condition exists in the engine, or the vehicle sits for a long time between uses.

Because of its location in the engine, replacing a rear main seal includes at least removing the transmission from your vehicle, if not completely removing the engine as well. Removing either the engine or the transmission from your vehicle is a difficult and time consuming job, usually making a rear main seal replacement a very costly project. This is why you hear so many horror stories about the unbelievable costs of fixing a leaking rear main seal.

The good news is that BlueDevil has created a way to seal your rear main seal leak easily and permanently without costly maintenance and long projects. BlueDevil Rear Main Sealer is a specially formulated additive that you add directly to your engine oil. BlueDevil Rear Main Sealer is not a petroleum distillate, powder, or hazardous chemical so it will not harm your engine in any way and can stay in your engine oil until your next oil change. Once BlueDevil Rear Main Sealer is in your engine it will revitalize the old seals you have, restoring them to their original size, shape and flexibility permanently sealing your rear main seal leak – guaranteed!