13 mondeo valve cover exhaust pipe leaks.

If the exhaust pipe leaks, try to replace the interface pad first, because the leakage may be caused by the aging of the interface pad. However, when several interface pads are changed and they don't work, you need to check them carefully.

Air leakage from the engine exhaust pipe will lead to oil leakage from the engine. The exhaust pipe can reintroduce the exhaust gas from the engine into the intake manifold so that the exhaust gas will enter the combustion chamber. The waste gas is nonflammable. After entering the combustion chamber, it will reduce the temperature of the combustion chamber and reduce the probability of knocking. Exhaust gas will also reduce the combustion rate.