When do differences in the numbers become meaningful?

South Carolina
I'm new to the site, so I hope this post makes sense. Say if oil A has a VI of 140 and oil B has 135, is this enough of a spread to make a difference? Or does it take a wider margin? Then how about other numbers such as pour point, flash point etc. I THOUGHT I knew a lot about oil until I found this forum.....man I'm just crawling while you guys are Olympic sprinters! [bowdown]


Staff member
Iowegia - USA
Let's take a 5W50 oil. It will probably have a large VI number, but that doesn't make it better. In fact, it probably has too many VII's to shear back and sludge up. The Borderline pumping temperature is the temp that determines just how low a temperature the oil can be pumped in the engine; the minimum BPT rating you will need is determined by the coldest temperature you will see in your area. I am not so interested in the pour point as I am in how low a temp the oil can be pumped. Too much has been made of flash point in my view. When dinos were the only thing around the flash point determined the source and quality of the base stocks. Flash point is determined by the base stocks AND the chemicals in the additive package, and higher isn't necessarily better. Search on "flashpoint" for the technical definition.