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  #1  
Old 11-05-2002, 01:12 AM
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Location: Vienna, WV
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Roll your own oil

I recognize that there is a risk associated with starting another oil
thread but I think I can add something to the subject rather than
rehashing the same old info. I got to thinking - "If Mobil can blend up
oil, why can't I?" That led to further wonderings along the lines of
"How close to 0W-40 or 5W-40 can I get mixing 15W-50 and xW-30?" Here's
what I've learned.

There is a well known rule that says if you mix oils of different
viscosities the log(Vis mix) = Frac A*log(Vis A) + Frac B*log(Vis B).
It's well known but tough to find references for on the web.

You can calculate viscosity at another temp if you know the viscosity at
2 temps using the equation
log(log(Vis+0.7)) = A - B*log(T-273).
You have to solve for A and B using known reference points such as the
40 and 100 deg C data published on the Mobil 1 web site. See referenced
spreadsheet. I'm sure there is more elegant solution than my trial and
error method.

You can calculate the Viscosity Index of a blend if you know the
visosity index, viscosity at 100 deg C, and viscosity at 40 C of an oil
with the same 100C viscosity as your blend. See the spreadsheet for
details. The formulas don't lend themselves to text.

You can get an exact viscosity match for Delvac 5W-40 using 28% Mobil 1
10W-30 and 72% Mobil 1 15W-50. I make no claims about TBN, HTHS or other
properties.

You can get reasonably close to 0W-40 using about 33% or xW-30 and 67%
of 15W-50. The 150 deg C viscosity is within 0.3 cP when the 100 deg C
viscosity matches exactly. See spreadsheet referenced below for details.
I didn't project cold weather properties of the blend but it will
certainly be better than 15W-50 and worse than 0w-40.

There is some interesting references to SuperSyn on the Exxonmobil
Chemicals website. Seems that they sell SuperSyn blending stocks. They
appear to be higher molecular weight versions of the standard synthetic
building blocks.

Here's a link that has a lot of basic info on viscosity. It's the only
reference I found with useful formulas for ASTM D 2270 Viscosity Index
calculation for V.I.s over 100.

Viscosity Principles

Here's a link to the spreadsheet I worked up.
Oil Blending Spreadsheet

Anyone see a downside to blending?
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1984 300D Euro
1995 S320
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  #2  
Old 11-05-2002, 02:55 AM
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The only thought that occurs to me are the additives per volume. How does one measure or actually know the additive ratios?

Or ... in the worst-case scenario, would a "blend" contain too much of a particular agent causing problems.

Very interesting idea never-the-less ..
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Old 11-05-2002, 02:57 AM
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Very clever and well thought out. You definitely got your money's worth in your CE program, but you do know what happens to guys that start new "oil" threads, don't you?
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Old 11-05-2002, 09:59 AM
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jbaj007, I thought the risk was worth taking. So far the responses haven't been too brutal.

haasman, I think it is a very good assumption that the various Mobil 1 grades have similar additive packages. I assume that Delvac 1 has additional detergents and TBN additives.

A blend of 2 materials, one with more additives and one with less, you will come out with something somewhere in the middle.
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  #5  
Old 11-05-2002, 11:55 AM
Bud
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Mobil 1 claim that their 15W-50 has more anti-wear additives than their other viscosities. Also, there is now some concern that Mobil/Exxon are now using a petroleum base for their 30 weight oils rather than the type 4 base used with the other ones.

Note that the Mobil 1 30 weight oils do not meet either of the Mercedes oil standards.

There have been debates about people doing their own blending of synthetic and non-synthetic oils and it's generally considered a dumb idea for more than one reason.
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Old 11-05-2002, 04:08 PM
PaulC
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I'm lost here. What advantage would mixing your own oils provide?
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  #7  
Old 11-05-2002, 06:52 PM
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PaulC, I started the project because I liked the idea of 40 weight synthetic and Delvac was 50 miles away and I didn't want to pay the dealer price for 0W40.

To be perfectly honest, any of the Mobil 1 synthetic oils will probably work fine if changed at reasonable intervals. When my S320 was new, 5W-30 to 10W40 conventenial oils where acceptable for 7500 mile changes. It seems that MB has since decided 40 weight oils are better for whatever reason. Probably because of warranty issues on the FSS vehicles with extended changes.
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  #8  
Old 11-05-2002, 07:53 PM
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Guess what Mobil 1 sells 0W-40 SuperSyn called European car formula which I will probably buy this weekend. I have heard that it is only available in quarts but Ill look for a case.
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  #9  
Old 11-05-2002, 08:51 PM
Bud
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Supposedly, you can now buy 0W-40 Mobil 1 at Autozone. This is the oil that was developed for Porsche and is now the oil recommended for any Mercedes with the FSS system. If you don't buy into the Mercedes extended change periods governed by the FSS system, you can now get the correct oil for interim changes outside of dealerships.
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  #10  
Old 11-05-2002, 09:50 PM
JetForeman
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Tom,

I tried mixing different weight synthetic oils in my old pickup and noticed that because of the different specific gravities, or the actual weght of the oil, that they would seperate over the course of a few days. So at startup my truck would be sucking in 20W-50 Amsoil which is not what I wanted.

I new that the oils were seperating after sitting a while because the Amsoil 20W-50 Series 2000 oil is red in color. I usually change my vehicles oil when cold so when I went out to drain the oil, bright red was the first to come out the drain, then it turned to a more brownish color. It also made a racket at startup too, so I had an idea that the oils were seperating after sitting.

Just my .02

Dale
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  #11  
Old 11-05-2002, 10:24 PM
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Dale, I'm not sure what was going on in your truck but I can assure you that the base ingredients in Mobil 1 grades are fully miscible. When 2 fluids are miscible they will not separate on sitting. A good analogy would be a bottle of Bourbon. The alcohol and water will not separate no matter how long the bottle sits.

On the other hand, I have observed that in a 1 gallon jug of Delvac 1, the last material out of the jug can be a little cloudy. I attribute this to some of the additives separating.

You may be interested to know that Mobil1 10W-30 has a higher specific gravity than 15W-50 (0.872 vs 0.863 respectivley.) the specific gravity of 5W-30 (0.862) is almost exactly the same as 15W-50. It's only a guess but I think that specific gravity decreases as the level of additives increases.
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