High oil shear

[Cefalu]

Blackstone just analyzed my oil and noted my engine was shearing my oil down a little, with a viscosity of SUS 78 and the cSt of 15.01. This oil was Redline 5-40 and there was probably 4,000 miles on the oil. Overall the engine has 73,000 miles on it.

 

How or why can an engine shear oil viscosity down?

Edited November 10, 2016 by Cefalu

[JFP in PA]

Without starting another "oil war", usually because of the starting blend stocks quality and/or the additive package is breaking down prematurely.

[DBJoe996]

Used oil is going to show signs of shearing.  You had 4,000 miles on your oil and it will exhibit loss of viscosity at that point.  Basically, oil loses it's properties over time/use.  That's what oil does and that's why you need to do an oil change.  Oil wears out.

 

Shear stability is a measure of the amount of viscosity an oil may lose during operation. Oil experiences very high stresses in certain areas of the engine such as in the oil pump, cam shaft area , piston rings, and any other areas where two mating surface areas squeeze the oil film out momentarily . Most multigrade engine oils contain special types of additives, called Viscosity Index Improvers, which are composed of very large, viscosity-controlling molecules. As the oil passes through the engine, these molecules are permanently sheared or torn apart over time, causing the additive to lose  its viscosity-contributing advantages which reduces the oils ability to maintain its higher number. ie.. 10w30 , 

Synth Oils do not rely as much on special Viscosity Index Improver additives and  will experience little  permanent viscosity loss. 

 

BTW - a synth 10W/30 has a value of 9.30-12.49 Cst's @ 100 deg C.  I would say your 15.01 Cst for 5W/40 @4,000 miles is nothing to worry about.

Edited November 10, 2016 by DBJoe996

[Cefalu]

I guess I was surprised at the breakdown at 4K miles because redline is supposed to be a premium "real" synthetic oil. My wear metals have been unchanged over the last 20,000 miles so it's not a poor product. But I replaced it with Joe Gibbs since I found it convenient to buy in Amazon. We'll see.

But Blackstone made it sound like my engine was harder on oil than a normal 996 engine, maybe I just misunderstood the way they phrased it.

Are 996 motors in general tough on oil?

[White987S]

20 hours ago, Cefalu said:

Blackstone just analyzed my oil and noted my engine was shearing my oil down a little, with a viscosity of SUS 78 and the cSt of 15.01. This oil was Redline 5-40 and there was probably 4,000 miles on the oil. Overall the engine has 73,000 miles on it.

 

How or why can an engine shear oil viscosity down?

Those are good numbers for shear stability. Red Line is a god product. By comparison, Mobil 0W40 would have been in the low 60's and under 12.

[JFP in PA]

9 hours ago, Cefalu said:

Are 996 motors in general tough on oil?

 

In general, yes.  They tend to run hot, which does not help, and can be generally hard on lubricants, which is why product selection and maintenance timing is critical.

[White987S]

42 minutes ago, JFP in PA said:

 

In general, yes.  They tend to run hot, which does not help, and can be generally hard on lubricants, which is why product selection and maintenance timing is critical.

Agree. And if you run the car in the powerband above the 4,500 rpm's during spirited driving. My cars see a lot of 4,500-6,500 rpm fun.