Date:         Fri, 6 Aug 2004 16:07:31 -0400
Reply-To:     "Daniel L. Katz" <katzd54@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Daniel L. Katz" <katzd54@YAHOO.COM>
Subject:      Re: Diagnosing a low (8-10 inches) vacuum gauge reading

john:

try measuring with gauge hooked to vacuum advance port, and at part
throttle. much can be learned using a vacuum gauge, both from overall
reading and action of needle.

cited compression numbers suggest a healthy engine.

dan

On Thu, 5 Aug 2004 02:24:26 -0700, jbclem1 <jbclem1@CHARTER.NET> wrote:

>My 1983 water-cooled is getting a lot of pressure in the coolant reservoir
(head gasket or cylinder
>spacer-seal or green o-ring, or cracked head?).  In the process of trying
to pin down which cylinder
>or side the problem was coming from I hooked up a vacuum gauge and
discovered a pretty low reading
>at idle (8-10 inches hg).  I'm not that familiar with the use of a vacuum
gauge and would like to
>hear some ideas about this low reading.  Everything I've read ties a low
reading to things like an
>intake manifold leak, late valve timing, brake booster leak.  A head
gasket leak causes the vacuum
>reading to drop sharply each time the leak occurs...that is not
happening, the low reading is pretty
>steady.
>
>Here is some other information:
>
>Compression test: 140-150 all cylinders
>Timing: set at 0 , if I set it at 5 ATDC the vacuum reading drops even
lower to 5 inches
>Engine rebuilt 10,000 miles ago
>Disconnecting individual plug wires, and also injector wires one cylinder
at a time causes the same
>change in rpm and vacuum reading for each cylinder...it is not evident
that any one cylinder is
>carrying more of a load than  the others.
>Very slight water usage, no steam or vapor coming out at the tail pipe.
>Isolating brake booster vac line doesn't change the vacuum reading (ie,
no leak in booster).
>Spraying Sure-start (ether spray) at all possible vac leak locations
doesn't show any change in rpm.
>
>This pressure problem has been occuring for about 6 months and doesn't
seem to be getting much
>worse, but it is very obvious and there's enough pressure in the coolant
reservoir to keep the level
>below the coolant level sensor, and to keep the overflow bottle full and
bulging a bit.
>
>Does anyone have an idea about this low vacuum gauge reading, and can you
suggest a way to connect
>it to this pressure problem.  I'd like to know more before I start
pulling off the cylinder heads.
>
>John