Russ Wilson writes :
>It's not a question of waiting long enough - a liquid just can't run out of
>a thin gap. Surface tension would, in fact, draw oil *into* an initially
>dry bearing.
>Has anyone ever known an oily surface to clean itself? When I
>What gives? Is this one of those myths that lives long enough to become
>"fact" or am I missing something? What does our oil expert say on this?
***
Hey there Russ,
Am I the "oil expert" you are refering to? If so, I appreciate the
compliment, but I must say that I don't receive compliments
such as this very often. I guess if I have to be an expert on
something, there are worse things than lubrication.
OK - now my opinion
Although I have no test results to back you up, I am inclined to
agree with your statements - at least mostly.
You are correct that surface tension, viscosity, and
probably dozens of other factors that only a physicist could
understand keep at least a layer of oil on previously oiled
surfaces. It takes quite some work to remove all of the oil from an
oiled layer. The forces holding the oil in place are normally
strong enough to fight gravity, and even time (to a point).
As to whether surface tension would draw oil into a dry area - that
is possible but not automatic. This depends on the geometry of the
situation, and I would imagine on other factors.
The major problem is that we are talking about engines - engines that
create heat and friction almost instantanously upon starting. Apply
a layer of oil to a piece of metal - no problem. Apply a layer oil
to an engine and then run it - another story.
Before you crank your engine, that thin film of oil will be there -
sitting and protecting. 5 years, 10 years, most likely even longer -
the oil will be there. However, crank that engine and that layer is
almost instantly wiped / pushed / pulled away leaving your engine
under-lubricated.
The persons (how's that for politically correct) talking about
waiting for oil pressure before starting are on the right track.
With pressure in the system, the thin layer of oil is quickly
replenished with new oil. This is especially important after storage
when all of the oil - except the thin film that will stick on the
metal - has had time to drain into the oil pan.
Actually, we've all seen the commercials and read the ads for these
oil additives that protect your engine even when your oil can't.
These compounds simply stick to the engine components better than
oil. Simple to understand - if they can stay on the metal and keep
lubricating, oil is not really needed. Do these additives /
replacements make sense? Again, that is another article perhaps for
another time - if people are interested.
OK Russ, OK guys and gals - does this answer the question?
BTW - are we always going to be stuck on this oil topic? Grease is
also an interesting subject. Did you know that there is a National
Lubrication and Grease Institute? Look on your grease containers for
the NLGI sign ! Perhaps we can all pile into our MGs and convoy
there sometime.
Ira M. Weinstein, Matawan NJ
'77 MGB
'88 Toyota Celica
'87 Nissan Sentra
'81 Honda CB650 Custom
(I'm the guy personally financing Allstate Insurance)
|