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The engine's primary driving force is the crankshaft, which is positioned low inside the engine block, typically just above the oil pan (also known as the sump). The crankshaft features counterweights that facilitate oil splashing to lubricate the main bearings.
To drive the transmission and crankshaft pulley, the crankshaft requires front and rear oil seals to prevent oil from escaping and to keep dirt and debris out. Over time, these seals can degrade, leading to oil leaks.
The replacement interval for these seals is not fixed, as they should only be replaced when they start leaking. The cost of replacing the rear main seal varies depending on the vehicle's make and model, ranging from $400 to over $1500.
The main factor contributing to the expense is usually the labor involved, as accessing the rear main seal requires removing the transmission from the vehicle.
What is a crankshaft rear main seal?
A crankshaft rear main seal serves an essential role in your engine. Located at the bottom of the engine, the crankshaft collaborates with pistons and connecting rods to harness the power generated from combustion. This rotational energy from the crankshaft drives the transmission, ultimately propelling the wheels.
Since the transmission's flywheel or flex plate is connected to the crankshaft, it protrudes beyond the rear of the engine. To prevent engine oil from seeping out through this gap and to shield the engine from dust and dirt contamination, a meticulously fitted rear oil seal is utilized.
Usually composed of natural or synthetic rubber, this seal is reinforced by a metal ring on the exterior. A slender spring maintains tension on the rubber against the end of the crankshaft, securing the seal in its place.
Over time, factors such as heat, poor engine oil quality, and the passage of time can contribute to rear main seal deterioration, leading to oil leakage. When this happens, the seal must be replaced to ensure the engine's optimal performance and prevent further issues.
