I normally use 20w50 in the summer " actually year round before knowing better " and wanted to try something different this winter as temps won't go higher than 20 celsius unlike summer days which will go above 40 celsius easily, can i use 15w40 or 10w40 or the car will eat the oil up like the cookie monster? People in my country " Egypt " advice against it they say " if you switch to a lighter grade the car will be damaged as the tolerance is used to the thick grades and any lighter grades won't give enough protection plus it will burn oil at much higher rate even if its not an oil burner " so is that statement true or just a myth? Can i change 1 grade lower in winter as ambient temperature is much lower