Carter Shore wrote:
>
> Seems to me that gap between the the bearings and
> journals provide the only path by which air could
> enter the system. Given the viscosity of oil, it's
> affinity for sticking to metal surfaces, and the
> tortuous path that it must traverse, I wonder how much
> of an issue this is.
A bigger issue than one might imagine. And, because, in fact, oil does
drain from the filter (that's not a notion, but an accepted reality),
one can assume that the oil in the system does not act as a vacuum
break. Air gets in to allow drainage. To illustrate the point, put some
warm oil on your finger. Does the resulting layer remain at several
thousandths thickness, or does it eventually drain and spread to an
exceedingly thin film? So, what happens in the bearings? The film breaks
between surfaces and allows air to enter the system.
And, when the engine is started, that filter must fill before the entire
system is pressurized. It's one of the reasons why most manufacturers
who have designed filter installations, usually due to space
constraints, which allow the oil to drain have specified filters with
anti-drainback valves in them.
What's the effect of the drainage on engine life? Sometimes, a
substantial one--we had a customer a few years back whose mechanics were
not filling the filters before installing them during oil and filter
changes. The projected lifetime before rebuild of the engines in the
service in which they were used was about 350-400K miles. The rate of
failure of engines with less than 100K miles was almost 15% of the
fleet, and this was directly attributable to running the engine without
oil pressure after oil and filter changes, and this was confirmed by
independent oil analysis.
Cheers.
--
Michael D. Porter
Roswell, NM (yes, _that_ Roswell)
[mailto:mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`72 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
`80 TR7 (3.8 liter Buick-powered)
`86 Nissan 300ZX (the minimal-maintenance road car)
`68 VW Type II Camper (Lancia twin-cam powered, but feeling its age....)
Remember: Math and alcohol do not mix... do not drink and derive.
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