Let's say an oil has a published Noack value of 6% (tested on a virgin sample). At the end of the oil's service interval, say 20,000 miles, would the used oil's Noack value still be 6%? Higher? Lower?
We know that most, if not all, lubricant properties change during use. I haven't see any discussion or data regarding how the evaporation rate changes, though. Just something I'm curious about in an academic/hypothetical sense.
I expect the answer is that there is some difference, but not significant enough to be meaningful.
probably depends on specific application.
if you have one of those honda 1.5turbo engines that can get into double digit fuel dilution..
that could be totally different from a port injected 2L elantra for example.
I had a similar question.
Easy to do an experiment - OUT of Doors on a hot plate. In a graduated beaker.
Its HAS to improve after an initial boll down.
The upper volatile solvents will "off" first.
So an oil may show 10% off in the first hour and then maybe 6% off in the next hour.
I agree that evaporation should decrease over time. But I suppose that the shearing effect over time also has an effect on volatility... shearing causes reduced viscosity / increase in lighter components? Maybe wrong, just a thought.