Kerry and all, please see responses inserted....
At 03:02 PM 9/12/2002 -0700, you wrote:
>Ok, We need a test case. I hear and understand what
>D2 is saying and actually agree with his words. I am
>struggling with the difference between the theory that
>D2 correctly describes and what I perceive to be the
>real world.
There are cases where the theory and practice differ. Often, this is
because the "theory" does not consider all the facts. There could be cases
that what I said earlier does not always apply.
>In my experience, if you have a car that smokes A
>LITTLE, especially at startup, then running Vavoline
>40 or even 50W racing oil (non detergent) will greatly
>reduce the smoking AND increase oil pressure.
Let's take one by one. I have heard from more than one person that the
single weight could reduce visible smoke. That does not necessarily mean
that it improves the lubrication. In fact, the wear rate could be higher,
even if smoking seased. The lack of smoke could be because the oil does
not burn but it just comes off the exhaust as droplets, or it burns but
more completely with less visible smoke, or that the oil supply to the
ring-pack is reduced, and I may be missing some for sure. We are certainly
dealing with a very complex problem which is hard to explain. The oil
pressure will increase at the lower speeds when cold, because the viscosity
is much higher. But that does not necessarily mean longer bearing
life. The interesting thing with journal bearings is that once oil
pressure is established (within a wide range of the values of pressure)
most of the time they either work without metal-to-metal contact (no wear)
or they seize (load too high or clearance to high), and there is little in
between. The only time they wear is when starting, so its far more
critical to get the oil there fast, than having a bit more oil pressure
when cold, or at low speed before the bypass on the regulator opens.
>The
>downside is that when it is VERY COLD (40 or less) it
>seems a little harder to crank and oil pressure does
>not pop up quite as fast but still pops right up.
That's exactly my point, this is the only time when the journals
wear. This is a very important drawback if engine life is important to you.
>What works for me may be because I have rather sedate
>driving habits but based on what D2 said, my solution
>would actually be better for hard driving except
>possibly for a few seconds at startup. After all,
>it's RACING oil.
Well, actually the straight 50 oil will have a far worse viscosity index or
VI (see prior message) than the 20w50 or Mobil 1 15w50. So, as far as ring
and liner wear are concerned, the 15w50 will do better. The oil pressure
will also establish better for the multi weight, so I really see no
advantage on using 50w (which kind-o looks like honey by the way, wondering
if it also tastes like honey!) except for reduction of visible smoke. Now,
why do they call it "racing"? May be it helps sales...
>A car which smokes probably has extra clearance in the
>journals and the heavier oil seems to take up some of
>the slack hence higher oil pressure. Yep the heavy
>oil can get SLOOW when cold but my thinking is that it
>will also stay in place on the journals while the
>pressure is coming up.
Good point. The main reason you need the oil pressure to build up fast is
the following. When you turn off your car, the bearing clearances are full
of oil that stays there, regardless of the oil. When the engine starts
again, there is a natural "back pumping" of the journal that actually
prevents this oil from coming off the gap, again regardless of the oil
(some machines with plain bearings can operate for years without new oil,
due to this natural back-pumping effect). However, what happens in an
engine is because the bearings rotate fast and are heavily loaded, this
quantity of trapped oil will overheat very rapidly due to shear and loose
its lubricity. Till fresh and cool oil comes from the oil pump, this
quantity of oil will not do very much. This is again where a high VI and
anti-wear additives help.
>Anyway, in 37 years of messing
>with old cars, this has worked for me and saved me
>several rebuilds because I won't drive a smoking car.
As said before, all oils are now so much better than they used to be, that
there is hardly "the wrong oil". If there is a difference between a good
oil and an excellent oil, you can only see it long term. And even then it
would really be hard to establish a difference because there are many other
factors that determine engine wear (like driving habits, climate,
etc). That's where these controlled tests help, and in all these tests,
the multi weights and synthetics are indeed better...
>If
>someone has a car that smokes a little (enough to be
>noticable and be able to tell if it smokes less after
>the test),
My green sedan smokes when started. I am sure it is valve guide seals
since performance is excellent and oil pressure very strong and climbs very
rapidly. I believe you, the smoke might reduce with the 50w. However, I
think its a small price to pay for long term performance and reliability (I
pulled a plug the other day that has been in there since 96, I didn't even
have to clean it. The car smokes at startup since 97). If avoiding smoke
is very important to you, then....
D^2
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