Why is my engine leaking oil on top?

The most likely reason your engine is leaking oil on top is a failing valve cover gasket.

Here's a more detailed breakdown:

Common Causes of Oil Leaks on Top of the Engine

Valve Cover Gasket Failure: This is the most frequent culprit. The valve cover gasket seals the valve cover to the cylinder head. Over time, the gasket material (often rubber or cork) can harden, crack, and lose its ability to create a tight seal. This allows oil to leak out onto the top of the engine. Valve cover gaskets typically need replacing every 20,000 to 50,000 miles, but this depends on the car's make, model, and operating conditions.
Loose Valve Cover Bolts: Sometimes, the bolts that secure the valve cover can loosen over time due to engine vibrations. This can compromise the seal and lead to oil leaks.
PCV Valve Issues: While less common as a direct cause of leaks on top, a clogged or malfunctioning Positive Crankcase Ventilation (PCV) valve can cause excessive pressure inside the engine. This increased pressure can force oil past seals, including the valve cover gasket, leading to leaks.

Visual Inspection: Carefully inspect the valve cover and the surrounding area for signs of oil leaks. Look for oil residue, drips, or a greasy film.
Check Bolt Tightness: Gently try to tighten the valve cover bolts. Be careful not to overtighten them, as this can damage the valve cover or strip the threads. Consult your vehicle's repair manual for the correct torque specifications.
Inspect the PCV Valve: Locate the PCV valve (usually on the valve cover) and check its condition. If it's clogged or damaged, replace it.

Replacing the Valve Cover Gasket: This is usually the best solution if the gasket is old or damaged. The process involves removing the valve cover, cleaning the sealing surfaces, installing a new gasket, and reassembling the valve cover.
Tightening Loose Bolts: If the bolts were simply loose, tightening them to the correct torque specification may resolve the leak.
Replacing the PCV Valve: If a faulty PCV valve is contributing to the problem, replacing it is a relatively simple and inexpensive repair.

Important Note: If you are not comfortable performing these repairs yourself, it's best to take your vehicle to a qualified mechanic.