How to Stop Engine Oil Leaks — Causes and Solutions
Finding oil spots under your car is a common problem, especially in vehicles with over 100,000 km. While oil leaks can seem alarming, many can be fixed with a simple pour-in additive — no mechanic needed. This guide explains the most common causes and the best solutions.
Common Causes of Engine Oil Leaks
1. Valve Cover Gasket
The most common source of oil leaks. The rubber gasket between the valve cover and cylinder head hardens and shrinks with age and heat exposure, allowing oil to seep out. You will notice oil dripping onto the exhaust manifold, causing a burning oil smell.
2. Oil Pan Gasket
The oil pan sits at the bottom of the engine and holds the engine oil. The gasket between the oil pan and engine block can deteriorate, leaving oil spots directly under the car.
3. Rear Main Seal
The rear main seal prevents oil from leaking where the crankshaft exits the engine to connect to the transmission. This is the most expensive seal to replace mechanically — often €800–€1,500 in labour because the transmission must be removed.
4. Front Crankshaft Seal and Camshaft Seals
These seals can dry out and shrink over time, causing oil leaks from the front of the engine, often near the timing belt or chain area.
5. Oil Filter Housing
Common on many European vehicles (BMW, Mercedes, VW), the oil filter housing gasket can leak, causing oil to drip down the engine block.
How Oil Stop Leak Additives Work
Oil stop leak additives contain seal conditioning agents that are absorbed by the rubber seals and gaskets in your engine. These agents cause the hardened rubber to swell back to its original size and flexibility, restoring the seal and stopping the leak.
What oil stop leak can fix:
- Valve cover gasket leaks
- Oil pan gasket seepage
- Rear main seal leaks
- Camshaft and crankshaft seal leaks
- Oil filter housing gasket leaks
- Any rubber seal or gasket leak caused by age and heat
What oil stop leak cannot fix:
- Cracked engine blocks or oil pans
- Stripped or damaged drain plug threads
- Corroded metal surfaces
- Missing or improperly installed gaskets
How to Use Oil Stop Leak
- Clean the engine first — Use an oil system cleaner to remove sludge that may be blocking or contaminating the seals
- Change the oil — Fresh oil allows the stop leak to work more effectively
- Add the stop leak — Pour the oil stop leak additive into the engine through the oil filler cap
- Drive normally — The product begins working within 100–200 km of driving
- Monitor — Most leaks stop within 200–500 km. Some stubborn leaks may require a second treatment at the next oil change
Finding the Leak Source
Not sure where the oil is leaking from? UV leak detection dye can help. Add the fluorescent dye to your engine oil, drive for a short time, then use a UV lamp to inspect the engine. The dye glows brightly at the exact leak point, making even tiny leaks visible.