Oil expert required

[DougR]

Hi folks, just running oil through the engine to check oil pressure etc., why is cheapo semi synthetic 5w40 denser than Duckhams 20w50? Surely it should be the other way around? Or are the components of the 20w50 separating? Any thoughts?
Doug.

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[Oneball]

I don’t know how viscosity relates to density but looking at the pic I’d suggest the difference between the two is because the one is full of heavy carbon and metallic particles or there’s a temperature difference

[Oneball]

Ps I hope you’re not thinking of putting that glass in the dishwasher

[Peter Laidler]

Ah, it's a chemist you need to speak to. The first part is the WEIGHT of the oil and one of the oils weighs more than the other, hence sinks to the bottom while the lighter oil (by density - not colour) remains on the top.

If you shake the contents, they'll mix and not separate.

Yoi can get the same effect with silicon and normal brake fluids in a small jar. But they will ALWAYS separate because one will not absorb the other.

[DougR]

This makes interesting reading....

https://totalenergies-eng.prowly.com/15 ... to%20water

Basically the density is not proportional to the viscosity. It depends on lots of different things like chemical composition, additives, age, moisture content, temperature, and it's arbitrary and nobody cares about it and that's why it's not written on the tin.

Now let's see how good this dishwasher really is.

[hanlminiman]

Way back in the 1960s we would call that a light & bitter in that glass served by the Phylis the "short" measure bar maid every time!

[DougR]

yeah over here it was known as a black and tan with the historical connotation - half Guinness half Ale, but it never got time to settle. . Must leave one sitting and see if they separate. .

[Hipwell]

The ‘weights’ of the oil is a measure of their resistance to flow at a set temperature.