Symptoms
- Oil accumulates near where the engine and transmission meet, underneath the car
- Oil may drip onto the transmission bell housing or starter
- Puddle location is further back than a typical oil pan leak
- Oil level drops steadily over time
Likely causes
- CommonWorn or hardened rear main sealThis rubber seal around the crankshaft wears with age and mileage, eventually letting oil seep past into the bell housing area.
- PossibleExcessive crankcase pressure pushing oil past the sealA clogged PCV valve or system can increase internal pressure, accelerating seal leaks.
- Less commonWorn crankshaft surface where the seal ridesIn higher-mileage engines, wear on the crankshaft itself can prevent even a new seal from sealing properly.
What to do
- Clean the area between the engine and transmission with degreaser and inspect after driving to confirm the leak location matches the rear main seal rather than a transmission pan gasket.
- Check the PCV valve and system for proper function, since excess crankcase pressure can worsen a marginal rear main seal leak.
- Distinguish oil (usually amber to dark brown, thinner) from transmission fluid (often reddish, sometimes with a distinct smell) at the leak point to confirm it's engine oil.
- Understand that this repair usually requires removing the transmission (or at least significant disassembly) to access the seal, making it a bigger job than most other oil leaks.
- Have the seal replaced by a shop, since incorrect installation can cause a repeat leak or other issues.
Tools and parts
- Degreaser
Rear main seal for your engineSearch: “rear main seal”
When to call a pro
See a mechanic for rear main seal replacement, since it typically requires transmission removal and is not a practical DIY job for most people.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.