Oil viscosity after usage

[UNC038]

We've all seen how some oils will thicken during the OCI due to oxidation in some engines. While other thin due to shearing or fuel dilution.

My questions are
1) If an oil (10w30) thickens does it also raise the winter number? If so, by how much generally.

2)If a 10w30 shears or get diluted does this effect the viscosity at 40 deg C.

 

[Bill]

97 GTP,

Review some of the used oil analysis (Used Oil Analysis),
I think most if not all Oil Analysis Labs test for viscosity at 100°C (212°F) but there may be some labs that test at 40°C (100°F).
If you find a used oil analysis with the oil thickening or shearing and the lab tested at 40°C you will be able to see how the oil changed viscosity wise.

I think an oil with fuel dilution will be thinner at 40°C (*W) and 100°C, the whole mixture of oil is diluted,
shearing of an oil is the VII (Viscosity Index Inprovers - additive) VII breaking down, coming apart,
so, the oil will not be as thick as new lube at 100°C,
I do not know if the actual lubricant is sheared, I would think NO, and the lubricant would still be in grade at 40°C.

Maybe someone with more insight can chime in

Hope this helps.

Bill

 

[UNC038]

Bill,

I know you can test the viscosity at 40°C for an additional charge. But I was wondering how time effected the viscosity at at 40°C in the two ways listed above, as this varies in different engines.

Since most engine wear occurs at startup, how does extended OCI effect the cold startup wear?

 

[Bill]

You would have to test the oil at 40°C during the OCI, when oil has to be added because of consumption, I would then test the oil then to see how much the oil has thickened.
The types of thickening I can think are Oxidation, boil off of lighter components of the lubricant, Soot? Insolubles?

I think Oxidation and boil off of the lubricant would make the lubricant thicker at 40°C, which would take the oil longer to pump through the engine but lubricants have Anti-Waer additives to counter act the wear at start-up.
If you look at the UOA area, you will find used oil analysis of oils that thickened with the interval but the wear is not high.

quote:

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Since most engine wear occurs at startup, how does extended OCI effect the cold startup wear?

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There are used oil analysis with oils that where used for long OCI, the oil thickened and the wear is fine.

 

[Bill]

97 GTP,

Here is a link to a question about the lube pour point changing after being used:

Pour Point Change

Hope the link above gives some info

 

[UNC038]

Thanks Bill, most interesting