How does fuel dilution affect HTHS viscosity?

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Direct injection + Low tension piston rings in modern engine design is causing fuel dilution to go through the roof. Yes, many blackstone UOA reports seem to indicate a relatively safe 1-2% fuel dilution but looking at the low KV100 & Flashpoint numbers, actual readings are probably closer to 5% or more. People who have resampled with Polaris labs (Using GC testing) reveals fuel levels much higher than blackstone.

Yes I know there have been topics posted before about cST shearing vs HTHS viscosity, but normal VII shearing of motor oil without fuel dilution is different than fuel dilution viscosity loss. My reasoning is that HTHS vis should hold up better with normal VII shearing, because the base oil isn't being diluted with fuel which isn't a lubricant (except for diesel).

For example: a virgin 0w20 sample has a KV100 of 8.7 & HTHS vis of 2.7.

If mechanical shearing from normal usage drops the KV100 down by 20% to 7cST, then you'd expect HTHS to drop 10%, down to 2.43cST.

If fuel dilution caused the same KV100 drop to 7cST, wouldn't the HTHS drop more than 10% since the base oil has been diluted? I doubt the VII polymers are able to bind with raw gasoline?
 
I can't imagine fuel diluted oil have hths issues simply due to physics. 2.5x the temp to boil water would surely force fuel to separate at a lightning fast pace. It would likely not stay diluted a moment after the forces are applied.
I'd like to be corrected if I'm wrong, but fuel (gasoline ) is so volitile.
 
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Fuel dilution will drop HTHS in proportion to how it drops KV40 & KV100, which can be quite a lot.
Yes gasoline is markedly more volatile than oil but because all hydrocarbons have an affinity for each other, the heavy oil molecules tend to 'keep' the light gasoline molecules in the liquid phase. Likewise when the oil gets very hot, the light evaporating gasoline molecules will 'pull' some of the heavy oil into the gas phase (which is why fuel dilution as often as not causes your car to burn oil).
In Europe, where we tend to use low SSI VII's, levels of real life permanent shear tend to be small to nonexistent. Most viscosity loss is attributable to fuel dilution, especially in diesels.
 
HKPolice,
best I've been able to glean, the half of the KV100 % loss (rule of thumb) still applies...been looking for a landing on that subject myself for a year+ m.now, still looking.
 
Originally Posted By: Shannow
HKPolice,
best I've been able to glean, the half of the KV100 % loss (rule of thumb) still applies...been looking for a landing on that subject myself for a year+ m.now, still looking.


Do you still have that paper handy? I'm sort of with sonofJoe with this, that by thinning the oil the kv loss will impact the HTHS much more than the temporary shear of the VII does. It's added on top of the mechanical shearing for a given shear rate.
 
On my DI DD, ~95%+ highway, it calls for 5w-20, normal duty 7.5k OCI's.
So I run 5w-30 and do 5k OCIs.
Maybe gives me an edge for fuel dilution, I dunno, but it makes it easy for me to remember the 5k OCI's and since its 5k, been using PYB.
At 5k, seems to have a hint of fuel smell but the sniffer is get'n old. Seems a little thinner to (the oil).
 
Originally Posted By: Shannow
HKPolice,
best I've been able to glean, the half of the KV100 % loss (rule of thumb) still applies...been looking for a landing on that subject myself for a year+ m.now, still looking.


Wow I guess I'll never find any hard test data if you're still looking
frown.gif
 
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