MJD running with different spec Oils

[dhans4all]

I guess 5w is low viscosity oil at cold temp than 20W. Lower the viscosity the flow of oil will be better hence its effective than 20w. Its my feel.

Generally lower viscosity oil is better for diesel engines.

Experts can comment here

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[cvanandh]

The first part of the oil grade refers to the oil's viscosity. For example, consider 5W-40. Here 5 refers to the temperature 5 degree centigrade and W refers to winter. The oil with W are tested in cold conditions. This is important in cold places for cold starting wherin oil's with low viscosity are of prime importance.

The above holds only for engine oil's. The concept followed for transmission fluids are different.

So, to put it simple, the advantages of a low W viscosity number is simple. The quicker the oil flows cold, the less dry running. Less dry running means less engine wear and better engine life

Hope this helps!

[jaya1973]

+1 ,

If u want to change engine oil and if the recommended grade for e.g. is 5w40 then the next best oil grade is 0w40 or 5w50

and in any case should not be 10w40 or 5w30

i.e. we cannot go above 5 for the cold grade and less than 40 for hot grade

[V Sunilkumar]

Just want to add few points. Lower the number on left side lower the viscosity at cold start. So the oil reaches all parts of engine compared to higher viscosity oil say 20Wxx.
Here you are focusing on engine wear and tear. On the other hand at high speed or continuous long drive we need a high viscous oil which will provide better lubrication than a thinner oil. So for better life of engine higher viscosity oils are best especially in hot climates. But thinner oils(no on right side of W) give better FE since they flow more freely compared to thicker oils but at the cost of engine wear as thinner oil provide less lubrication. I have read on net that for older cars the thinner oils are not good since it may take the good dirt from engine. The ideal solution will be synthetic oils which generally give better range for both conditions.