What is mean by 15w40 , 20w40 grade in Lubricant oils. how can we choose lub oil for our vechile.?

how lubricant oil has classified. how we choose correct. diff between 15w40 - 20 w 40.





what differance for same grade oil for Differents. shall we use all brand oil ( like Shell, Castrol, Mak, K-Oil) for our engine in same grade.???What is mean by 15w40 , 20w40 grade in Lubricant oils. how can we choose lub oil for our vechile.?
15w-40 has a cold cranking wieght of 15... (w for winter) and is a 40 weight at operating temp, so it'll flow a little better then the 20w-40. Synthetic oils usually come in a wider range of viscositys like 0w-30, 5w-40 and such. Takes alot... too much volume index improvers and such for conventional, that the oil would go out of grade in no time... different manufacturers have a small difference in wieghts... one may be a high 40 wieght, the other a low 40 weight at operating temp. Just sticking with name brands insure quality.What is mean by 15w40 , 20w40 grade in Lubricant oils. how can we choose lub oil for our vechile.?
the grades refer to viscosity and composition of the oil. Your vehicle manual should have instructions on the type to use. make sure you don't mix synthetic and standard oils