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Discussion Starter · #1 · (Edited)

As with many I had been swayed by the reasoned arguments on BITOG and other forums that running a grade lighter than OEM could be beneficial - primarily via more rapid flow/lubrication during lower temperature start-up and faster heat removal at operating temp.

The argument has also been made that at operating temp (100C) - the dynamic/kinematic viscosity of a 0W-40 is the same as a 5W-40; or that at 20C (room temp) the viscosity of a 5W-30 is the same as a 5W-40 or a 5W-20.
The latter is categorically untrue, while the former is quite brand dependent.

Whether this supports or negates the primary rationale for running lower grades, I cannot say, but there are clear viscosity differences between similar grades and more critically - between manufacturers.
I do not have the equipment to answer the question as to Min Oil Film Thickness (MOFT) at a given viscosity - but I presume it does correlate monotonically with viscosity - and thus I personally will err towards those weights and oils that preserve as much viscosity as possible at 100C or 150C (HT) - and secondarily have a lower cold temp viscosity where possible.

My primarily motivation for performing this analysis was to examine a sample of Pennzoil Euro Platinum 0W-40 at 1 year and 2K miles to determine if it remained 'in grade'.
As it turned out the answer was no and yes.
No - at room temp (20C) it graded as a 5W-30 (not necessarily a bad thing).
Yes - at 100C - it graded as fresh Amsoil 5W-40 (EFM) or Pz Euro Platinum 0W-40.

Test Setup:
The tests were done at 20C and near 100C using a thermally regulated 100ml Burrette and measuring the time to flow 5,10,15.20, and 25ml of the sample under test (and measurements at 30ml were added for the 100C tests).

Patience is required as at room temp it takes about 80 minutes to flow 25 ml;
compared with about 5 minutes at 100C.
In some cases tests were performed several times to demonstrate repeatability.

Viscosity of these lubricants is extremely temperature sensitive - even 1C variation creates a measurable difference in flow rate.

100C Results:
DT40 5W-40 in Orange at 100,101C
Penn Euro 0W-40 in Blue at 86,98,102 C
Amsoil 5W-40 (EFM) in Green at 99,102C

If 100C Viscosity is what matters - DT40 outperforms the others by maintaining higher viscosity at 100C.
I presume this carries over to High Temps (150C).

My used Penn Euro with 2K miles and 1Yr (taken from 2009 QP-S) graded as fresh Amsoil/Pz Euro.

Penn Ultra Platinum 5W-30 and 0W-20 (Yellow shades) - are - as expected - quite a bit less viscous than the #W-40s at ~100C.

The 'cold' 86C Penn Euro (upper blue trace) is noticeably more viscous than same at higher temps.

For reference:
20C Water is at bottom Dark Blue and 70% IPA in Purple.
20C water has a a Kinematic Viscosity of 1 cSt.

Colorfulness Rectangle Slope Plot Font

Room Temperature 20C Results:
PZ Euro 0W-40 is - as expected - less viscous than its 5W-40 brethren.

Used PZ Euro 0W-40 grades as a 5W-30 at room temp (though not at 100C where it remains 'in grade'.)

Colorfulness Slope Rectangle Plot Font

For my QP-S I have switched to Driven DT40 for its better 100C (and presumed HT) viscosity and Molybdenum-rich additive package.
It rarely freezes where I live so am less concerned with low temp viscosity.

I am really impressed with Pennzoil Euro Platinum 0W-40 holding its 100C grade at 2K miles/1 year.
In a cold climate this is an excellent choice and it is about half the price of DT40 or Amsoil EFM.



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