Thicker is not better. It is a necessary evil where needed
when engineering tolerences are gross. Thickness hinders
flow. Formula 1 engines typically use *very* thin oils.

 

That is what I use.

 

Ease of flow is often too much as in the case of Mobil 0W40. Film thickness and shear strength are much more important especially in the lower quality engines Porsche has been producing for the last 9 years. Too fast of a flow will also increase oil temps in these engines as the coolant has less time to absorb heat while the oil passes through the cooler.

Once up to operating temperature and under pressure, the same amount of oil flows whether it is the 5W50 approved by Porsche or the 15W50 or 20W50 which is not.

 

By what criteria are these newer engines lower in quality?
If we presume you mean the engineering tolerences, you
are claiming they have increased. If so, Porshe would
recommend a thicker oil, unless you're suggesting that
Porsche is not only making looser motors, but doesn't
know it.

I think there's a logical fallacy there. The same speed
of flow also exposes that same oil to less time to absorb
heat from the hot parts of the motor, so it is less hot
when it enters the cooler. It is much better to keep oil
relatively cool than to let it get really hot and then cool
it down, however efficiently. And note that viscosity is
liquid friction. It *causes* heat in the oil. One interesting
fact is that thermal breakdown in oils is not linear with
viscosity. All oils burn/become gum above a certain
temperature, and the hottest parts of our motors do stay
in that range, so the only hope for the oil is to pass it
through fast enough so no part of it stays long enough to
get that hot, and thicker oils will be 'hotter-on-arrival'.

Is there no oil pressure relief valve?

 

Mobile 0w40

 

Another aspect of this is that it would be expected,
because all those oils are designated to behave the
same at 100 degrees C. They differ in how they will
behave at lower temperatures. Startup is an important
wear consideration. Some estimates claim a majority of
engine wear/damage occurs then. A cold motor that has
had most of the oil settled down into the pools and galleys
needs a thin oil to flow quickly to the exposed parts. It
has been said that no oil is thin enough for startup. That
is a logical reason why Porsche would recommend 5w50,
but not 20w50.

 

Mobile 1 0w-40. I figure the engineers at Porsche know best.

Adam

 

The greatest contributer to wear at cold startup is NOT oil flow but condensation. Unless you are starting your engine in sub freezing temperatures, a 15W oil will get around the engine just as fast as a 0W will. As a matter of fact, there will be less oil needed to fill the system as more of the 15W oil will have remained where it should be. A 15W oil has less leakdown than does a 0W.

As for tolerences.....I wonder why people would think that the engines are tighter today when Porsche allows up to 38 quarts of oil to burn out of the engine every 15,000 miles before they will say there is a problem. Must be some close tolerances in these engines.

 

I'm intrigued by Protomotive's choice of Valvoline 20W-50, as Todd and Cynthia Knighton clearly know their stuff, but so does Stephen Kaspar who has torn down lots of 996 Turbo motors and says thicker oils cause valve train issues.

Is there a right answer?

 

Tell me how condensation causes wear. (And note that condensation
is independent of oil viscosity) I will try to find the article I read about
Formula 1 engineers having considered using water as a lubricant.
So far as I know, condensation puts water into the oil, and this water
can combine with combustion by-products to produce acids that hurt
motor parts. The best practice is to always run the motor long enough
to reach full operating temperature for several minutes so it boils off any
condensed water, and to change your oil frequently enough that it never
runs out of the base additives that are put there specifically to react
with and neutralize the acids.

The definition and test of viscosity is the rate of flow. By definition
a 15w oil flows more slowly than a 0w oil at 0 deg. C., and the thinner
oil will go into the smaller spaces like plain bearings and valve train
spaces much faster than a cold thicker oil.

So the thick oil *does* flow more slowly, but only when it's beneficial to
do so? And the length of time from motor shutdown till the next morning
is plenty of time for *any* liquid lubricant to have drained away from
elevated parts. 'Leakdown' as far as I know is a term to do with cylinder
compression testing, and certainly to the degree that there are gaps
in rings and cylinder walls, a thicker oil will block leakdown in a stationary
leakdown test, better than a thin one. Epoxy would be even better, but
that does not say which will be better in practice overall in a running motor.

I think it *may* be a matter of safety. Note that the tolerances that
affect oil consumption are a very small subset of the motor's lubrication
areas and tolerances. It may be that Porsche does allow more of a gap
in cylinder wall and some valve guide clearances, so that they avoid the
possibility of siezures, at the cost of higher oil consumption. That might
be a good tradeoff, especially given the low expense of topping off.
However, I would prefer that Porsche was more explicit in that regard,
because I too would be annoyed by a motor that consumed more than a
quart per 1000 miles. If they were more descriptive of this, it would
preclude the impression that some people get, that oil consumption means
the whole motor is a clatter-trap of loose fittings. In fact, given the cont-
inual gain in machining accuracy due to enhanced computer control, I
bet the truth is that the majority of motor tolerances like the various
bearings and valve train components are superior as a whole, and closer
to what is designed, than those in the typical Porsche motor of the 80's
or 90's.
Joe

 

Thought this pic was appropriate for this thread. Took it yesterday of a mechanic friend of mine that pulled this motor to rebuild because of a blown head gasket. Oil was all in the cooling system, the coolant resevior, and all the way to the front radiator. I have no idea why the owner has that specific plate.....its real, not photoshop..

 

There are many published articles detailing the damage at startup caused by condensation in the combustion chamber. The damage happens long before the engine is hot enough to burn it off. The point I was making is that oil flow is such a minute (maybe 15 -20% of engine wear) when compared to the condensation in every engine at cold startup, especially those run in humid climates. Just take a look at your mufflers in the morning. There is as much water in your engine as in your mufflers. This is exactly why you can get triple+ the miles on any engine if you never shut it down compared to allowng it to cool and then starting it up again. I think it was Hot Rod back in the 60's that demonstrated this fact using a preoiler to eliminate oil flow concerns. Engine tear downs clearly showed the damged to the piston, cylinders and valves from the water and steam.

Oil flow under pressure is far different from flow by gravity which is how viscosity is measured. Just because something flows more slowly when you pour it does not mean it will flow at the slower rate when pressure is applied.

 

The tooth fairy say 0-40 (does not have to be Mobil 1)

 

Why does Porsche say to not use 20w-50 then? (my take on the article in Excellence and the sum of oils on the "ok" list at present)

 

Interesting! I'll look that up. A separate issue from oil, but interesting...


Can you point me to anything to document this? I will do some
researching myself too , but all I was taught indicates that as oil
is functionally incompressible, it's flow is precisely determined by
pressure, divided by viscosity.