Oily stuff - 5W20

[Grant Lenahan]

This is why i began my original post as i did.  At say, 100 degC a 5w40 and a 30w40 should have identical viscosity. The difference is that at 0 degC the 5w will flow and the 30w will, well, flow slowly.  I won’t get into the gory detail of how theory and reality differ, but start there.

5w50 is the “dc to light” oil.  Its thin when you need it thin, and thick when you need it thick. The problem is, in making such oils, even with modern synthetic base stock, you compromise other qualities. Let’s not go there.

Here’s a reference:  for most common synthetic 5w40 oils, at 40 degC they have a (kinematic viscosity) of around 70 cst.  At 100 degC they have a viscosity of around 15 cst.  M1 10w40 by comparison has a 40 deg cst of ~100 and 100 degC cst of ~15

Note only the cold measure moved drastically.  note also that when cold both are VASTLY thicker than either at 100 degC (operating temperature).

Ergo, one must think about the curve they form, the consequent viscosity at the temperature you expect them at, and the viscosity that you motor needs.

or, as has been said, follow the manufacturer’s latest recommendations. They did this for you.  in most cases running a good A3 rated 5w40 meets all needs, except track use. For track use i throw it all away an go thick.

Grant

On Dec 4, 2014, at 1:24 PM, Mike Claire <mike.claire at gmail.com> wrote:

> Huw, I thought I was following you until you said you run 5W50 in your
> 90Q.  I thought your argument would be that anything less than "10" is too
> thin for cars of our vintage.
> 
> If Rotella T6 5W40 for my S4 AAN is good, I'll do it as I already stock it
> for my '01 S8 4.2 V8.  My oil shelf's running out of room - different oils
> for all 5 cars and a tractor!
> 
> 
> 
> Mike
> 
> On Thu, Dec 4, 2014 at 9:23 AM, Huw Powell <audi at humanspeakers.com> wrote:
> 
>> John is correct.
>> 
>> The idea of looking at the numbers on oil and "deciding" whether or not to
>> use it makes no sense.
>> 
>> Engines are built to certain tolerances and require certain fluids to
>> function properly.
>> 
>> In the case of oil, there is a viscosity range recommended (which may vary
>> slightly depending on conditions), from a "cold" end that allows sufficient
>> flow for lubrication at start up to a "hot" end that maintains enough
>> viscosity for adequate pressure to be developed at "running" temps.  Keep
>> in mind that "running" temps are pretty much the same no matter how
>> (reasonably, like >= -40 deg) cold the ambients are.
>> 
>> Just because a new weight range turns up on the shelf doesn't mean it's a
>> new good thing for your engine.
>> 
>> The "standard" used to be 10W40, with a few deviations, and a few
>> requirements for synthetics.
>> 
>> The standard for the last couple of decades has run towards 5W30, with
>> many calls for 5W20, 0W20, etc., often requiring OEM/dealer sourced oil
>> coming in the last decade.  These engines have far tighter tolerances and
>> thus build plenty of pressure with the thinner oil, saving energy - and
>> also, well, having tighter tolerances.
>> 
>> These simply are not correct for our cars.  If you aren't sure, check your
>> owner's manual and use either what it says, or try something slightly
>> thicker if you are consuming a lot (> 1 qt/1000 mi, or even >1 qt/tankful
>> of fuel).
>> 
>> I like 5W50 synthetic for my 90Q - easy cold starts, no fears of it
>> getting too thin when I am in "oil-cooled" mode.
>> 
>> - Huw
>> 
>> 
>> On 12/3/2014 11:46 PM, John Larson wrote:
>> 
>>> On 12/3/2014 2:32 PM, Tihol Tiholov wrote:
>>> 
>>>> To keep list traffic going, here's a general question. Anyone with
>>>> thoughts, experience, etc. re: this oil? Isn't it too narrow a temp.
>>>> range,
>>>> esp. for the Graet White North? I don't, nor intend to use it, just
>>>> curious, since it's taking over the shelves at FLAPS.
>>>> 
>>>> Tihol
>>>> 
>>>> It's important to remember that modern "thin" oils are required for use
>>> in modern engines.  Tolerances are tighter, oil passages are smaller,
>>> and the engines are designed to utilize thinner oils to aid in fuel
>>> economy.  Older designs, such as all the I5 engines and nearly all their
>>> contemporaries don't do well with thinner oils because the passages are
>>> relatively large and clearances are loose. The results of using oils
>>> made for the newer designs are lowered oil pressure, and most likely
>>> increased oil consumption.  Porsche, as well as Mercedes, use 0w20 as a
>>> factory fill.  Scary, huh? Knowledgeable techs and shops put 5w20 in 'em
>>> ...
>>> 
>>> John
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