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Date: Fri, 23 Mar 2012 09:20:09 -0400
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From: Gary Casey <casey.gary@yahoo.com>
Reply-To: Gary Casey <casey.gary@yahoo.com>
Subject: Re: Crankcase "venting" after flight
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My disagreement is, I suppose, more quantitative that qualitative. =A0Yes, =
the vent tube is low compared to the filler tube, so air will rise in the v=
ent tube, be heated and then flow into the engine, presumably purging the "=
bad stuff" out the filler door. =A0This convective action takes place only =
while the engine is hot, so it dissipates rather quickly - as Brent propose=
s, the most effective time is soon after shutting off the engine. =A0But th=
e effectiveness depends on the internal design of the engine, which most ce=
rtainly was not based on this type of venting after shutdown. =A0On many (m=
ost?) Continentals, the vent tube is connected directly to the filler tube,=
 making any purging of the crankcase pretty much impossible. =A0Lycoming en=
gines have the vent at the rear and the filler somewhere else, giving at le=
ast a possibility that some purging could take place. =A0I guess I'm just n=
ot convinced that the benefit is worth the potential risk. =A0As anecdotal
 evidence, I received one private reply from a practitioner that said he fo=
rgot to put the cap back on "only" twice.=0AGary Casey=0A=0AFrom Brent:=0AL=
etting the crankcase vent after a flight is a good idea. It is a better ide=
a after a short flight where the oil has not been hot for long, after low a=
ltitude flights where the vapor pressure is low relative to the crankcase p=
ressure or in humid climates.=0A=0AOpening the oil cap will cause air to fl=
ow in the crankcase vent and out the filler due to convection. Most of the =
crankcase vapors will likely be displaced in the time it takes to secure th=
e airplane. Secure the cap and close the door when ready to leave. If you h=
ave to walk away with the cap off, flag the oil door with a "Remove Before =
Flight" banner.=0A=0ABrent Regan=0A
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<html><body><div style=3D"color:#000; background-color:#fff; font-family:bo=
okman old style, new york, times, serif;font-size:12pt"><div>My disagreemen=
t is, I suppose, more quantitative that qualitative. &nbsp;Yes, the vent tu=
be is low compared to the filler tube, so air will rise in the vent tube, b=
e heated and then flow into the engine, presumably purging the "bad stuff" =
out the filler door. &nbsp;This convective action takes place only while th=
e engine is hot, so it dissipates rather quickly - as Brent proposes, the m=
ost effective time is soon after shutting off the engine. &nbsp;But the eff=
ectiveness depends on the internal design of the engine, which most certain=
ly was not based on this type of venting after shutdown. &nbsp;On many (mos=
t?) Continentals, the vent tube is connected directly to the filler tube, m=
aking any purging of the crankcase pretty much impossible. &nbsp;Lycoming e=
ngines have the vent at the rear and the filler somewhere else, giving
 at least a possibility that some purging could take place. &nbsp;I guess I=
'm just not convinced that the benefit is worth the potential risk. &nbsp;A=
s anecdotal evidence, I received one private reply from a practitioner that=
 said he forgot to put the cap back on "only" twice.</div><div>Gary Casey</=
div><div><br></div><div><span class=3D"Apple-style-span" style=3D"color: rg=
b(69, 69, 69); font-family: arial, helvetica, sans-serif; font-size: 13px; =
">From Brent:</span></div><div><span class=3D"Apple-style-span" style=3D"co=
lor: rgb(69, 69, 69); font-family: arial, helvetica, sans-serif; font-size:=
 13px; ">Letting the crankcase vent after a flight is a good idea. It is a =
better idea after a short flight where the oil has not been hot for long, a=
fter low altitude flights where the vapor pressure is low relative to the c=
rankcase pressure or in humid climates.<br><br>Opening the oil cap will cau=
se air to flow in the crankcase vent and out the filler due to convection.
 Most of the crankcase vapors will likely be displaced in the time it takes=
 to secure the airplane. Secure the cap and close the door when ready to le=
ave. If you have to walk away with the cap off, flag the oil door with a "R=
emove Before Flight" banner.<br><br>Brent Regan</span><br></div>  </div></b=
ody></html>
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