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Oil mixing...does density matter? #5334723 01/28/20 02:02 PM
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LotI Offline OP
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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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Re: Oil mixing...does density matter? [Re: LotI] #5334728 01/28/20 02:06 PM
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csandste Offline
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Others know more than me but I'd be really surprised if oil separates. If you miss 5w30 with 5w20 it doesn't restratify once you drive it.


2017 Kia Soul Plus-- Valvoline Daily Protection 5w30+ a bit of Harvest King syn 5w30-- 75,000 miles
Re: Oil mixing...does density matter? [Re: LotI] #5334745 01/28/20 02:34 PM
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kschachn Offline
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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.


1994 BMW 530i, 251K
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Re: Oil mixing...does density matter? [Re: LotI] #5334783 01/28/20 03:41 PM
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Imp4 Offline
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Here is an excellent thread discussing the subject.
Thanks to Shannow and TomNJ for the included content.
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3503628/Re:_The_oft_quoted_ASTM_D6922


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Re: Oil mixing...does density matter? [Re: LotI] #5334810 01/28/20 04:37 PM
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Lou_Boyle Offline
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All the distillation and fractionation equipment oil companies use to separate crude oil into different components is proof they won't separate naturally.


Think carefully about what you are doing, but be decisive. The road of life is paved with flat squirrels who couldn't make a decision.
Re: Oil mixing...does density matter? [Re: LotI] #5334823 01/28/20 04:56 PM
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csandste Offline
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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.


2017 Kia Soul Plus-- Valvoline Daily Protection 5w30+ a bit of Harvest King syn 5w30-- 75,000 miles
Re: Oil mixing...does density matter? [Re: LotI] #5334843 01/28/20 05:28 PM
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They make blended oil (different densities) already, don't they?..so you are fine.

Re: Oil mixing...does density matter? [Re: LotI] #5334846 01/28/20 05:35 PM
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I used to mix oil all the time a few years ago. None of the engines I added it to ever died.
Blend to your hearts content! thumbsup


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Re: Oil mixing...does density matter? [Re: LotI] #5334873 01/28/20 06:08 PM
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eljefino Offline
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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.

Re: Oil mixing...does density matter? [Re: LotI] #5334897 01/28/20 06:45 PM
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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.

Last edited by danez_yoda; 01/28/20 06:45 PM.
Re: Oil mixing...does density matter? [Re: LotI] #5334912 01/28/20 07:14 PM
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So if the API says it’s miscible they mean anything, huh?


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17 Mazda6 GT
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Re: Oil mixing...does density matter? [Re: LotI] #5334923 01/28/20 07:32 PM
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Motor oils are a blend of different base stocks and viscositys.


2015 F150 2.7
2018 F350 6.2
Re: Oil mixing...does density matter? [Re: LotI] #5335353 01/29/20 10:52 AM
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kschachn Offline
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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.


1994 BMW 530i, 251K
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