Date: Sun, 5 Dec 1999 14:27:18 -0600
Reply-To: John Rodgers <inua@SCOTT.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@SCOTT.NET>
Subject: Re: Heat gauge
Content-Type: text/plain; charset=us-ascii
Way back when....I was was involved with the aviation industry. Many airplanes had
and still do...use aircooled piston engines. In the beginning the configuration of
the cylinders were radial, or in a circle around the crankcase. Later they were
built opposed much like the aircooled engines of the VW Beetles, the 411's, and the
various VW Vans, even unto this day. There were two cylinder, four cylinder, six
cylinder and eight cylinder versions. All, flat, all opposed.
To keep up with the temperature situation on the engines, cylinder head temperature
guages were installed, and the temp sensor was a washer and wire of disimilar metals
that went to the guage. The guage washer replaced the normal spark plug washer. As
the washer got hot the dissimilar metals produced a current that could be presented
on the guage as a representation of temperature. This gave some idea as to
temperature but it really measured only the temperature of the specific cylinder to
which it was attached.
As time passed, the desire to have more specific information on the engines pushed
the temp sensor idea into multiple sensor mode. A washer and wire setup was put on
each cylinder at the spark plug, with a switch, so that each cylinder could be
selected, individually. The entire engine could be monitored that way, and when
recorded, over time could be used as a diagnostic tool if there were problems.
The washer wire setup was slow however, and a better system, the Exhaust Gas
Temperature Guage, or EGT, was developed. This involved having a high temp probe
installed in the exhaust manifold just a few inches from the exhaust port of the
engine, With this sensitive probe, the temperature and any tiny changes could be
monitorted. It could be used to determine if the engine was running lean, or rich or
right at peak temperature. Typically for best power the fuel air mixture would be
adjusted by the pilot until the engine ran at peak temperature ---he would lean and
the needle would rise.....peak, then as he continued to lean the mixture, it would
begin to drop back Right at peak temp, he would enrich the mixture until the exhaust
gas temperature cooled by 50 degrees. There the mixture would be set. That allowed
best power with out heat damage. This was a tremendous improvement over the old
washer/wire/guage arrangement. But in the biginning it was applied downstream far
enough in the exhaust to sample gasses from several cylinders after it was all
mixed together.
This was an improvement. But still there was the need to sample all cylinders. As
time passed these systems evolved into full sampling systems, and would have a probe
for each individual cylinder. It is the ultimate temperature guage.
Recently I blew a cylinder in my 2.1L. It hasn't been torn down yet to see the
actual insides, but "0"compression on #3 cyl plus welded aluminum on the spark plug
indicate a meltdown and a hole in the piston. That means internally that cylinder
was running at or hotter than peak temperature....something that points to an
overlean condition.
If there was an aircraft type EGT probe in the exhaust manifold a couple of inches
from the exhaust port, I would have been able to see on a guage there was someting
wrong. If I had all four cylinders wired with probes, I could have made comparisons,
and the spread would have certainly caught my attention. and perhaps I could have
done something before I had and engine failure.
I am about to rebuild my engine. I am looking into the EGT situation. If I install a
system such as an EGT I will post the list as to the progress.
This may be something you might like to look into.
Would appreciate comments from the list.
John Rodgers
"88GL Driver
Zoltan Kuthy wrote:
> I hope someone of the upper echelons will read your question and will answer it
> professionally and not in the all knowing male ego style. Guessing and brain
> storming welcome too. I use oil temperature gauge but I guess that is not quite
> enough. Let us see if there is someone who knows.
>
> ZOLTAN
>
> Samuel Chimento wrote:
>
> > Question??
> >
> > Since the valve seats drop out by over heating the air cooled engines in the
> > Vanagons then
> > what heat gauge is the best to install so that you can keep a close eye on it
> > and prevent the
> > problem.
> >
> > Thanks
> >
> > Sam
