oil is oil right? To a point. (long)

[Dan <dturlik@xxxxxxxxxxxxxxxxxxxx>]

I've always wondered what oil was the best for my cars, I've gone back 
and forth between Amsoil and Mobil 1 as well as some other synthetics and 
non-synthetics.  I have ready all the info on the newsgroups, dejanews, 
the oil faq's floating around.  I did my own research, by fishing through 
many companies web sites, and requesting product data sheets.  Recently I 
decided to throw some money at the problem.  I ran Amsoil and Mobil 1 in 
our BMW.  I had the oil analyised after ~10,000 miles +/- 200 miles.  The 
results were not very astonishing.  The spectrographic analysis revealed 
*very* little diffenernces.  The Mobil 1 did oxidized quicker but it kept 
its viscosity better then the Amsoil.  I was curious about the results so 
I called the lab's technical services dept.  I started milking this guy 
for knowlegde.  We talked for a while about the subject of oil.

Here are some key observations of his (remember, this is not your uncle 
Cecil, but someone whoe looks at the results day after day) :

1.  Up to 5k mile drain intervals, there isn't a whole lot of difference in 
oils, in fact he said you couldn't make a case for any oil in that short 
amount of time.  He said that analysis would indicate very similar rates 
of wear.

2.  After ~5k miles, the regular oils start to break down, they oxidize, 
loose their viscosity, and stop protecting your engine as they were 
designed to do, wear rates increase after this point.

3.  After ~10k most synthetics start to break down, wear increases. Mobil 
1 starts to lose its cool after ~12-15k.  Amsoil at ~15-17k.  After that 
its all down hill.

4.  All oils get dirty from engine pollutants, like dirty air, fuel 
by-products and fuel contamination, but this does not seem to effect the 
rates of wear very much.  Most of the wear causing stuff is caught by the 
filter and the actual wear occurs when the oil starts to break down, NOT 
the pollutants in it.

5.  Mobil 1 is THE superior oil overall with consideration to price.  

6.  If you change at 3-5k intervals you are pouring your money down the 
drain with synthetic oils.

7.  Synthetics pour at lower temperatures, but the wear rates are not 
signifigantly different when compared to regular oils.

Now what I'm wondering is what is BMW thinking, either they don't care 
how much wear occurs, or they are allowing for some signifigant wear with 
their drain intervals because they are pushing the limits.  10k with 
regular oil and 15k with the new long life stuff?  I dunno, but I think 
10k intervals with Mobil and 5k intervals with Castrol GTX (good specs 
for a regular oil) are safe and give you the best bang for the buck, 
anything longer and you run the risk of increased wear.  i'm going to try 
the 5k interval with Castrol GTX and I'll report the results. 

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End of bmw-digest V9 #270
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