Just when you thought this thread was dead ...
Fired up the BJ8 for a short hop to pick up my uncle on Sunday. Was curious,
so with the engine running at a fast idle
(1,000RPM or so) I took the oil filler cap off the valve cover and put my hand
over the filler hole. I was a bit
surprised to find there was fairly significant vacuum, enough to seal the palm
of my hand over the hole. I've always
assumed there was enough air leakage to keep the crankcase pressure near
atmospheric, even with the PCV valve. I'd
guess several inches of vacuum (if I get ambitious maybe I'll try to get an
accurate reading with a gauge). There was
no difference in idle speed or otherwise with my hand over the hole or not.
So, the pseudo-PCV 'system'--with no deliberate fresh air source--maintains
vacuum in the crankcase and valve cover,
instead of circulating much air like a true system would (there may be
significant leakage through the filler cap,
though). This is good in that the PCV isn't causing the rear cylinders to run
lean--would probably have burnt a valve
by now if it had--and the vacuum probably helps reduce oil consumption and
leaks.
Can't think of a downside to this, except maybe that not circulating fresh air
isn't helping control pollution, but then
again maybe it is. My oil doesn't get very dark, even after 5K miles or so.
Bob
--
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Bob Spidell San Jose, CA bspidell@comcast.net
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