<VV> Re: viscosity vs temp

[James Davis]

I reiterate current synthetic motor oil of the SL and SM variety get 
thicker with heat cycles.  Oils I use are Mobil 1, Castrol Syntec, and full 
synthetic Super Tech.  All show more oil pressure at idle (500 rpm) at 230 
degrees F and at cruise 3,400 rpm at 276 degrees F after 500 miles of 
use.  The pressures remain up until the oil change at 7,000 miles.
Jim davis

At 12:46 PM 7/3/2005, djtcz at comcast.net wrote:
> >
> > Anyone with a digital oil pressure gauge, using synthetic oil, can easily
> > verify that, indeed, the oil's viscosity index decreases (oil gets 
> thicker)
> > as the oil cycles over its heat range.
> > Jim Davis
> >
>http://www.mpc-home.com/htmls/viscosity%20chart.jpg
>
>If I understand the question right, I think the answer is >>not<< that 
>synthetic gets thicker when hot, but rather that it does not thin out as much.
>If, at 100C an oil's viscosity is ~15 cst it would be labelled 40 wt.  If 
>at that temp it was ~11 cst it the label should be 30 wt.
>
>At 40 C (not an SAE test temperature) they both would be over 100 cst.
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