Mazda 0w20 W/Moly Oil, 2013 I4 Accord, 6651 Miles

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Originally Posted By: MikeySoft
Originally Posted By: CATERHAM
Originally Posted By: MikeySoft
Yes, I refilled with the same MGMO w/Moly 0w20 oil. Do you have a comment about the VI?
Yes the VI drop to 188 is a little disappointing but it's still higher than the virgin VIs of most 0W-20s. We also don't know if it's main competitor, TGMO fairs any better. All we do know is that the latest TGMO version appears quite shear stable in most applications. Of course this is just one UOA under harsh winter conditions. I think the next UOA if it is taken no later than December with the likelihood of less fuel dilution will be more telling.
But the fuel dilution was less then 0.5% ? I'm not sure how useful VI is because most likely viscosity is nonlinear with temperature but only uses 2 points to compute, the lowest one is 40C. I would thing viscosity at 0C and lower would be more important.
You're right viscosity change with temp's is non linear, in fact viscosity has a log relationship with temperature, meaning in effect that the colder the oil gets the greater will be the change in viscosity. Two factors affect this rate of viscosity increase with temperature as temp's drop, the oil's VI and the oil's grade. 20 grade oils thicken less as temp's drop than 30 grade oils even with the same VI and 30 grade oils thiken less than 40 grade oils etc. Of course the higher the VI of the 20 grade oil the less it will thicken vs other 20 grade oils of the same KV. The following Viscosity Graph predicts kinematic viscosity based on the KV40 and KV100 spec's: http://www.widman.biz/English/Calculators/Graph.html Regarding fuel dilution, yes it was only 0.5% when you had the oil tested but fuel does degrade oil. So over the 10 month OCI it could have contributed to the viscosity loss. That's one reason why viscosity lose can be very much application specific. That's why I suggested you're next UOA before next winter sets in to see the affect under more favourable conditions.
 
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I should add that if you plot out the VOA spec's and the UOA you'll see that the viscosity lose almost compensated for the VI loss. At 32F it's KV had increased about 8% but that put it on par with a virgin TGMO.
 

JAG

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Originally Posted By: CATERHAM
I should add that if you plot out the VOA spec's and the UOA you'll see that the viscosity lose almost compensated for the VI loss. At 32F it's KV had increased about 8% but that put it on par with a virgin TGMO.
Polymeric viscosity index improvers affect viscosity more at 100C than they do at 40C. When some are broken apart and permanent shear results, the permanent shear will be more prominent at 100C than at 40C, hence the VI drop.
 

JAG

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Also, keep in mind that every UOA has some fuel in it. Fuel will decrease the viscosity more at 40C than it will at 100C, so fuel added to oil increases the viscosity index of the mixture. The effect is very significant. Check it out quantitatively using Widman's site's mixing viscosities page. Also remember that Blackstone's fuel percentages are underestimated, so don't assume 0.5% or less fuel content. Over 1% is a more reasonable set of numbers to assume.
 
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Anyone have Sulfur PPM for the mazda oil? - I would imagine the high Moly could be an issue for Hybrid use if the Sulfur contribution is high.
 
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