The rear main seal seals the crankshaft where it exits the back of the engine. Because replacing it usually requires removing the transmission, it pays to confirm the diagnosis and install the new seal correctly the first time.
Confirm the Leak Source
Oil at the bottom of the bell housing is not always the rear main seal. Valve cover gaskets, oil pan gaskets, oil galley plugs, the oil filter adapter and the camshaft plug can all drip into the same area. Clean the area, add UV dye to the oil and use a UV light to find the actual source.
Common Causes of Rear Main Seal Leaks
- Age and heat hardening the seal lip.
- High crankcase pressure from a restricted PCV system or worn piston rings.
- A grooved or damaged crankshaft sealing surface.
- Excessive crankshaft end play or main bearing wear.
- Incorrect installation, such as a cocked seal or a lip that was rolled over during installation.
Installation Tips
- Inspect the crankshaft sealing surface. Light marks can be polished, while a deep groove may require a repair sleeve where available.
- Clean the seal bore and housing completely, and replace the seal housing or retainer gasket if equipped.
- Install the seal square, using the correct installer, to the specified depth. Do not hammer it in at an angle.
- Follow the instructions about lubrication. Some modern seals, including PTFE types, must be installed dry.
- Check the PCV system so excessive crankcase pressure does not push oil past the new seal.
Evergreen Rear Main Seals
Evergreen offers rear main seals and seal covers in gasket sets and seals. Many Evergreen full gasket sets also include a rear main seal. Use the Evergreen eCatalog to confirm the right part for the engine.
