Date:         Sun, 3 Feb 2002 22:40:52 EST
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      Re: Coolant pressure gauge mounting
Comments: To: hilltech@netins.net
Content-Type: text/plain; charset="US-ASCII"

In a message dated 2/3/02 6:47:06 PM, hilltech@NETINS.NET writes:

<< In a closed hydraulic system, such as the cooling system in our
Vanagons, the pressure everywhere in the system is very, very, nearly
equal.   >>

A note of disagreement here. As I just indicated in a reply to the question
posted, there is a difference in magnitude of signal (pressure change) and
rate of response. As indicated in Chuck Hill's response, the pressure should
be constant in a closed hydraulic system ... except for compliant systems
(hoses), pressure drops (across radiator, small channel tubing) and flow
restrictors (heater circuit).

As I was searching for the right location, I tested three areas ('82 Diesel
Vanagon configuration), to wit the coolant reservoir tank, the radiator bleed
valve and the heater inlet line just before the flow control valve. As I
recall (age damaged neurons and the general passage of several years since
the event). The heater line response was poor and sluggish, and only behaved
intelligently when the flow valve was open. All the same high pressure
responses were seen on the radiator tap, but they were muted (several psi
less than the recovery tank. Never did see the 1 to 2 inch negative pressure
at the radiator over night.

Remember, the system shows many transient phenomena. The pressure at the
water pump inlet is lower than the pressure at the outlet. Etc, etc.

I'm tired! A pressure gauge anywhere is good. Far better than none. If you
are disturbed by rapid gauge movements (thinking that they distract you from
the formidable process of driving) then mount it in the heater loop. If you
enjoy the excitement and thrills of rapid gauge response mount it in the
coolant reservoir. If you want to diagnose the state of the cooling system
instead of concentrating on SWMBO's latest diatribe about attention paid to
oncoming traffic, mount three! Than is, one in the reservoir, one on the
radiator bleed screw and a differential one to monitor the real time
differences in front to back pressure.

Frank Grunthaner