My car corolla gli 2010 is almost 120k driven , engine seem in good condition, I had this car for almost 2 years now and always change the engine oil on 3k intervals ,using 10w40 mobil super 1000 oil. Recently my car is driven almost 2k after the last oil change and now when I opened the engine oil cap its full of dark oil sludge, where as the dip stick indicator shows the oil is clean enough. How did the engine sludge builtup inside oil cap and surrounding please help is this something to worry about.?
