Date: Wed, 21 Jul 1999 19:54:47 -0700
Reply-To: Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Young <young@SHERLOCK.SIMS.BERKELEY.EDU>
Subject: Re: "Smoke in the Cockpit!!!"... Vanagon Drama in Real-life,
Part , Deux
In-Reply-To: <01BED3A3.323DE640@ip70.raleigh10.nc.pub-ip.psi.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII
It sounds like you've had two Great Adventures with this motor, which is
two too many; the panic attack alone probably takes a year off your life
each time. Glad to see that everything worked out OK in the end.
However, I don't agree with some of the things you said about the EGR system:
On Wed, 21 Jul 1999, Bulley wrote:
> What is relevant is that when functioning correctly, the EGR system
> includes a burning hot pipe running through the motor compartment to the
> intake manifold. That pipe can be hotter than the muffler of the van.
I've had my '81 since it was new and it's always had a functioning EGR
setup. I've grabbed that pipe many times and, while it certainly could
be warmish, no way was it close to being as hot as any part of the
exhaust system. (Just to make sure of that, I went out on a 15 or so
mile jaunt and then grabbed the EGR pipe; I could hold it easily.) In
fact, my FI harness has ALWAYS touched the EGR pipe on its way over to
the left side of the engine, and hasn't (as far as I can tell) affected
it a bit.
That makes sense to me because very little exhaust is actually passing
through the pipe (none at all at idle and WOT) because of the metering
gasket that sits between the pipe and valve. That gasket has an opening
of something like 1mm, so the most exhaust by volume that could pass on an
intake stroke is something like 55 or 56 cubic millimeters, vs. the
492724 cubic millimeters a stock piston will draw. Also, that exhaust is
passing through an expansion chamber (EGR filter) sitting out in the
ambient air, so it has to take a pretty big temperature drop from its
entry into the EGR pipe to its exit out the EGR valve.
Also, none of my manuals make any mention that I can recall right now
about the "danger" of the heated EGR pipe.
Are you sure the EGR pipe got that hot, and it wasn't simply a case of
chaffing of the insulation of your wire?
> While the EGR system is important for environmental reasons, it is
> also essential for cooling the motor. Yes, that's right, by
> introducing exhaust into the intake mixture, the overall combustion
> temperature inside the cylinders is lowered significantly.
I don't have the science behind me to challange this in any quantitative
way, but my instinct is that this is not exactly right. Yes, I know the
EGR lowers combustion temperature, but I don't know by how much and by
how much (if any) the overall heat of the engine is affected. (There's a
certain amount of energy in a given quantitly of gas and as far as I
know, the same quantity of gas is burned by an EGR-equiped vehicle as one
that's not so equiped).
I guess my reasoning on this (such as it is) is that the Type IV motor was
originally designed without and EGR valve and the original motor had a
cooling system that was deemed adequate to the purpose. The impetus
behind adding the EGR valve was pollution, not engine cooling. Ergo, the
EGR is not an essential component for cooling the motor.
> Malfunctioning EGRs tend to cause dropped or burned valves and burned
> pistons, particularly #3 and #1 in the type 4 motors. These were the exact
> cylinders that had dropped valves in ours...
Well, I guess if I'm going to take the position that the EGR setup is not
an essential cooling component, then I have to take issue with this too.
The EGR empties exhaust gases into the air distribution box where it
mixes with all the other air drawn in via the AFM, so I don't know why it
would have some particular affect on #3 and #1. Yes, the EGR valve
empties into the air distribution box closer to #3 and #1 then to #4 and
#2, but my instinct (not science) is that the mixing is pretty
thorough. I would guess, however, that #3 and #1 might be more prone to
heat-related problems just because they are further away from the intake
fan than #2 and #4.
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Tom Young young@sherlock.SIMS.Berkeley.EDU
Lafayette, CA 94549 '81 Vanagon
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