Phosphorus-free engine lubricants are gaining importance for preventing catalyst poisoning which is the major deactivation mechanism that causes the malfunction of 3-way catalysts. The main purpose of this paper is to evaluate the mechanism of surface layer formation on combustion chamber of spark ignition engines with phosphorous-free and phosphorous-containing engine lubricants. An experimental endurance test was conducted for 100 h at equal load conditions for each lubricant. Endurance tests were applied with a laboratory engine test bench. Subsequently, engines dismantled and cylinder liners were cut accurately to obtain specimens for microscopic examination. Optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy methods were used for evaluation.