There are two oils of the same SAE grade 15w40,out of which one has a viscosity of 110 cSt at 40°c and other has a viscosity of 115 cSt at 40°c.Which would be better to select.

not possible to answer.
If you want to base your choice on the viscosity you should check the VI (Viscosity index) where you get an idea on how much the viscosity changes vs. temperature.

Hi Mr.Hughes,

There is a concept that higher viscosity at 40°c oils will resist dilution problems rather better than low viscosity at 40°c oils.Is there any truth behind this concept.

never heard that before. Personally I would belive that is not true, because evt. dilution of other fluids would acure because of each fluids specific gravity (sg). Fuel and oil has approx. the same sg and therefore would mix easyly, nomather what viscosity.

- I might be wrong..

Hallo Krishnakumar,

I agree with mr. Hughes, even higher viscosity oils will lose their inherent functionality with regard to viscosity if continuously diluted and this can not be remedied with selecting a higher viscosity.

Assuming the application is an engine, by the oil grade referred to, you should perhaps approach your OEM and speak to them about a something like the CUMMINS Centinel. It extracts a certain volume of oil from the sump and dispenses it into the fuel while "sweetening" the oil by topping it up. Rely on simple timer system and replenish oil at a fixed rate regardless of engine’s duty cycle.

It will definitely not solve major fuel dilution problems BUT it prolongs your oil drain intervals, reduce maintenance costs and convert used oil to productive energy - it is not a sales pitch but mere information sharing and I hope it does not add to confusion.

Have a great day.

Krishnakumar,

Multigrade Engine oils tends to get VI shearing
due to the oil molecules gets squeezed at loaded bearing zones.Inadequate Base oil/Polymer
formulation results in permanent shear and subsequent drop in viscosity,eventually results
in premature wear of Engine components.

Hope this helps....

Regards

Bala.

It depends on the components/ package that go into the product. The base oil quality , Viscosity Index Improver, and additive content and performance.

Normally you should consider the viscosity@ 100'C for engine oils and even further Viscosity shear values@ 150'C