Mobil 1 oil weight

Tue May 1 22:11:39 EDT 2007

I'll lean toward ensuring remaining film strength, based solely on 
personal experience.  Three I5 turbos that blew or burned oil on the 
light stuff, and one (stock S6 AAN) that fired up with a shrieking turbo 
and valve clatter after sitting five days and thereafter shrieked on 
boost until I got the light oil out and 15W50 in.  The valve clatter in 
the urq (driven rarely) was so bad that I didn't put 100 miles on it 
before I changed the oil out.  The RS2'ed S6 avant just burned oil and 
got the worst mileage it ever had...which the S6 sedan did, too.  I have 
to believe, despite over extended statements of Dr. Haas, that more 
damage/wear was done to all three engines in the time they had that oil 
in them than in all their previous miles.  My guess; the light stuff 
drained out of the hot, turbo'ed engines to completely and there wasn't 
sufficient film protection remaining on the engine and turbo bearings or 
at the head/valves at startup.

Better base stocks are only better based on the tests chosen.  Doesn't 
really say much about real world for a given car and engine, much less a 
particular owners driving characteristics and habits.

I had a 1608 cc Fiat 124 Sport Coupe that I sold with 178k on it that 
had only seen 20W50 GTX...except for the summer when I worked near the 
Salton Sea/Mexican border and ran 60 weight Valvoline racing oil (hey, 
it was 112F at midnight!).  When sold, compression in all cylinders was 
at the top0 of new spec.  The engine had hot street cams, dual dual 40mm 
Webers and a free flow exhaust.  It never burned a drop of oil and 
embarrassed various P-cars with its' power and customized suspension and 
did lots of canyon runs and got 30+ mpg cruising I5 at 75-85 mph during 
many super slab blasts from Stanford to L.A.  All on that much maligned 
dino oil and 3000  mile oil changes.

Find an oil that works and change it when it needs it.  For NA cars, 
unless they are seriously hi performance, I don't see the need for 
synthetics, unless you live down here in the humid gulf where moisture 
finds its' way into everything and do lots of stop and go traffic and 
are lazy about changing oil.  Synthetic, lighter weight, for newer tight 
tolerance turbo engines.  Same rules apply about finding an appropriate one.

FWIW, the modified Alfa 2 liter coupe I had at the same time didn't run 
nearly as well on GTX.  Its' engine preferred the viscosity 
characteristics of Valvoline 20W50 racing, so that's what it got.  Seems 
someone several years ago posted that their S4 (C4) seemed to prefer 
Amsoil 15W40 Diesel oil. Had an Amsoil tech tell me he wasn't surprised 
and that he thought it was one of the best oils they made.  It worked, 
and I hope he's still using it.  I may have to give it a try, since 
ordering it may be just as easy to get an oil I want right now.

If 0W30 works for you, Grant, great..really!  If you do end  up with 
engine problems however, do let us know.  Ameer, whatever you decide to 
run is fine with me.  Again, let us know how it works out.  I have three 
cars and two of them don't see lots of duty anymore, so I will make sure 
they have higher vis synthetic in them as they sit here in Houston 
humidity and will TRY to make sure I fire them up and take them out at 
least once a month.

Steve

Grant Lenahan wrote:
> I saw this earlier, but didn't have time to respond intelligently - you 
> raise important issues, although you dont sway my conviction. let me 
> explain why.
>
> Most people agree with you.
>
> Historically, oil and motor manufacturers agreed with you.
>
> But 3 things have changed:
>
> 1.) think oils can be made from much better base stocks. Most 
> synthetics begin with the higher weight base (eg: 40), and flow well 
> naturally. Most dino oils  started with the lower weight (e.g.: 0) and 
> then added VI improvers to meet higher temp demands.  These VI 
> improvers dont work all that well (low VIs) and wear out, leaving you 
> with thin oil.  Synthetics dont.
>   
Which means that they last longer and don't have to be replaced as 
often.  But, 'improvers" with dino oil can still meet most hi temp 
demands  at a much lower cost point than synthetics.
> 2.) Research has shown that to maintain oil flow, and thus good 
> lubrication, almost all oils are too thick until operating temperature, 
> at least, is reached. read Dr. Haas' articles (all 10 of them) before 
> countering this.
>   
Counter what?  That's why multi-vis oils were developed.  Nothing new or 
shocking at that.  Technology advances and we get better at addressing 
that point as time moves on.
> 3.) Further research has proven the old farmers' tale true. A paper 
> from the last SAE conference in fact.  >90% of all engine wear occurs 
> during startup and cold running. Not just "dry cranking", but 
> insufficient flow to meet the demands of rpms above idle.  This can 
> occur very, very low.
>   
Again, the reason for multi vis oils.  Your premise is that you will 
always have better flow/fluid transport with lower vis oils.  That isn't 
true.  There has to be a balance, which is addressed for a particular 
engine and oil passage dimensions by a particular viscosity.  We are not 
pumping in a completely filled and closed system.  The oil pump as to 
effectively pick up and move that fluid.  It's a whole lot easier to 
pick up a fluid with some minimal/substantial viscosity than to pick up 
and move something with a viscosity like water.  Unless the oil in use 
has the properties necessary to maintain a minimal film strength for the 
time period the engine is expected to be shut down, after operating 
under the conditions and temperatures under which it is shut down, it 
will cause more damage to the engine than a short transient oil 
starvation before pressure comes up.  Again, it's related to the design 
of passages and tolerances in a given engine.  Tests with laboratory 
standards, or on one particular type of engine don't necessarily relate 
to another given engine and (although I hate absolutes and think that 
this whole discussion is caught in trying to apply results globally in 
absolute terms) I would venture to say, ABSOLUTELY do not apply to all 
engines.  That doesn't mean the findings aren't valid; it just means 
that there are other factors modifying their validity for a particularly 
case.
> The last two say the industry was always wrong, if well intentioned.  
> Long held beliefs change slowly.
>
>   
It doesn't say the industry was wrong!  It just said they addressed the 
problems by a different means with the technology of the times.  We knew 
that 95% or engine wear occurred at start-up when I was a kid...and I'm 52!
> You are very right that older motors have larger tolerances. You are 
> also right that they require a thicker film to fill this void, maintain 
> pressure and protect. But this can happen two ways:  1) higher flow, 2) 
> thicker oil.  With insufficient pressure and pump volume, thicker oil 
> wont solve the problem.  Dr. Haas shows this is often true below 100 
> degC.
>   
Look at what you said, "with insufficient pressure and pump 
volume"...There are the proviso's...do you think Porsche, Audi, Ferrari, 
MB ensured that there oil pumps were designed to provide the pressure 
and flow requirements for the oils specified?
> I dont know where the line is drawn. The only way to end this 
> conclusively is to monitor both temperature, and flow, and pressure 
> simultaneously on various motors. That would be a very worthwhile 
> research project.  It might even cut list volume by 80% :-)
>   
Agreed, but you have to include the aforementioned shut down temperature 
and static time and measure film strength and thickness, too.
> Would I go a bit thicker in an older I5? yep. But I used 5W30 (M1) in 
> my I5s with great results.  Dr. Hass' research and calculations show 
> that these oi;ld (5w30, ow40) are too thick for modern motors ( at 
> least above idal),. So, using your own logic, they may in fact be 
> perfect for older ones. Without data its just speculation.
>   
Got my data...3 out of 3!  Not a coincidence, in my experience.
> Bottom line is more damage is done by thick oil in cold engines than 
> thin oil in hot ones.
>   
Again, depends on what's left on the engine surfaces and how well it 
protects relative to initial oil 'starvation'.  Just 'cause you got thin 
oil doesn't mean it will pump efficiently through the engine at startup.

I just remembered a screw-up of mine with the Fiat after the summer down 
near the border.  I hadn't changed the oil back to 20W50 after heading 
back up to school in the fall.  And time just kept slipping, because I 
rode my bike and the car basically sat there with only occasional 
use...for three months.  Just didn't get around to changing it because, 
heck, it only had 1500 miles on it.  Came Thanksgiving and a spur of the 
minute ski trip to Mammoth and an unexpected blizzard.  After four days, 
dug the car out, remembering the race oil as we dug.  I was sure it 
wouldn't turn over.  But it did...and fired each cylinder so that you 
could hear it and see the engine turn with each pulse.  The damn thing 
just kept going and eventually started to run faster and faster and 
warmed up and we were off, everyone shaking their heads in disbelief at 
what had happened...and at how the car nut could be so stupid.  That 
racing oil had helacious film strength, but still a low enough viscosity 
to allow the engine to turn at about 20F.  Granted, that's not at -5F, 
but it was enough so that, starved as the engine was for circulating 
oil, it was able to function.

Boy, that was a ramble.  That's what happens after listening to a Jr. 
High School band concert....

Steve

Ol' Fart ex-Engineering Prof and some kinds of fluid flow specialist