I just had a 12k service and noticed a rise in the oil pressure in general. Does the oil lose some of its viscosity or body over time?
I did a few track days and drove the car hard most of the rest of the time and now am thinking that maybe i should change the oil around the 6k mark instead. I was surprised by the difference in pressure and also the fact that the engine is definitely less rattly.
Cheers.

 

Multiple factors could be involved.

1 - Are you sure the viscosity of the oil you got
was the same as you had? Same brand?
2 - The viscosity retention additives can degrade over
time, so that could make new oil thicker at operating temps.
3 - If there is any blow-by, gasoline can dilute/thin oil over time.
4 - In the other direction, the more volatile components of oil
can evaporate away over time, making what remains thicker.
5 - Over that period, what did you top off your oil with? The
same as installed?

Joe

 

Are you sure you have the same amount of oil in your car now compared to what was in it before the change. You might have been low before and have the right amnount now, or, as is common practice at the dealer, they mistakenly put in 1 or 2 more quarts than they should have. Check your oil level.

 

A rise in oil pressure would indicate more viscosity, not less. You will notice that old oil is thicker at room temperature than it was when it's new...

 

Oil shears some, the sliding metal parts break the oil molecules into shorter (less viscous) pieces. On the other hand oxidation of the oil causes molecules to cross link and form bigger (more viscous) chains. Sometimes old oil gets thicker and sometimes it gets thinner.