Oil mixing...does density matter?

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Theoretically. This crossed my mind as I was looking at my oil stash spreadsheet(nerd!). If I were to mix my most dense oil, Valvoline Premium Blue 15w40(.880) with my least dense oil, RGT 0w-20(.833) would they mix homogeneously our would they separate if left sit for a period. Just a thought. I wouldn't mix these oils unless the virus has completely taken over civilization and I had to!
 
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Only if they are immiscible which isn't going to be the case with those two oils. Also ASTM D6922 (part of SAE J300) addresses that, and if the oils pass that standard then they will not separate. Different viscosity motor oils don't have that wide of a density range either.
 
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There was no Bobistheoilguy in the mid sixties. But this is one of the first oil questions I ever asled. Guess I was in my early twenties and I'm mid-seventies now. Put some 10w40, noticed my new used car was full of 10w30 and called the selling dealer panicked. The answer was the same then as it is now.
 
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I rebuilt my saturn engine way back in the day and wanted to break it in with random leftover 1/2 quarts. Put some 10w40 in, 5w30, straight 30, whatever. Drained it 200 miles later. Most of the oil came pouring out in a stream. But there was a dribble of drops coming out concurrently. Was it one of the random ingredients? We'll never know. Filled the engine with all-the-same stuff afterwards and never saw this phenomenon again.
 
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in the interest of science. Pour a could of teaspoons of each in a glass container. Add some food coloring to one so you can see. Lightly mix (dont blend bot lightly mix) put the jar in a old pillow case and swing it around (outside) as hard as you can to make a centrifuge. Then check it after to see if the heavy stuff settled to the bottom or stayed mixed.
 
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Originally Posted by LotI
So if the API says it's miscible they mean anything, huh?
You asked about two specific oils, both of which according to their websites are API SN licensed. Therefore both must pass ASTM D6922 as part of that license and will be miscible. It won't depend on the density however, that is also what you asked about. Miscibility of one liquid hydrocarbon in another is not about density.
 
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