Date: Wed, 13 Feb 2002 11:14:04 -0600
Reply-To: Stan Wilder <wilden1@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: gauge recommendations
Content-Type: text/plain; charset=us-ascii
This is about air cooled........... sort it out and decide which gauges
you need.
----------------------------
Being somewhat of a cynic I installed two oil temp gauges (just happened
to run a shielded six wire bundle).
The first gauge was to the sender in the oil sump plate with the VDO
gauge and sender from Bus Depot. The second sender was mounted in the oil
pressure bypass port using an Audi 5000 sending unit and OEM Audi gauge.
(second gauge now removed)
Historically I got temperature differentials of ten to twenty degrees
from the two locations.
At highway high temperature operation the oil temperatures about balanced
within ten degrees but after a forty five minute (from cold) town run the
sump plate sender read 20 degrees higher temperatures than the bypass
port sender.
The overall temp was about 200 in city driving. The overall temp for
highway driving got as high as 266 degrees in very heavy loading (70-75
mph and accelerating up hills and fighting head winds). Under normal
highway driving I managed to keep moving at 65-70 mph and maintain a 220
degree reading.
If you just reduce your speed or otherwise un burden the engine cool down
from highway operating temperatures requires about thirty + minutes to
loose 40 degrees of temperature from the oil.
If the vehicle is stopped and the engine is off then the cool down cycle
is shortened to about 20 minutes to loose 40 degrees.
This idiot method of testing was done when outside ambient temperatures
were at about 90 degrees.
I evaluate reducing engine burden just as effective as spinning the fan
faster and in effect fewer explosions in the chamber less heat.
There are certainly times when having the engine at peak torque (4200
rpm) is preferable to slowing down and effective use of the capable
gearbox is dictated to maintain the peak power range required to climb
hills.
You won't be seeing any rocket response from an oil temp gauge since the
oil temperature is slow to build and long to reduce.
Cylinder head temperature reading is more responsive and will give fairly
accurate readings within three to five minutes.
How the two gauge readings truly relate is still somewhat of a mystery to
me. I can run 380 CH and 204 oil temp. Conversely I can run 350 CH and
240 oil temp.
In most of my trips that are 130 miles straight down an Interstate my
gauges all settle in and seldom move; the oil pressure 50-55, oil temp is
220, cylinder head temp 350/360, volts 14.
If the situation changes as in fighting head winds or climbing long
inclines the first reading to change is the CH temp. I may be well past
the hill and starting a new one before the oil temp even wobbles out of
temperature changes that took effect and are currently reversing.
So I've got to go along with Bob Donalds in his statement that Gauges are
mostly toys of a sort and too much dependance on the insignificant
changes in the readings is just unneeded stress.
In the one event in seven years when I blew #3 ring lands and badly
scored the cylinder while running 85 MPH against a head wind, I saw the
oil on my back window five minutes before it showed up on the idiot
light. I didn't have an oil pressure / temp gauge or cylinder head temp
gauge at that time but I'm sure I'd have seen excessive oil temperature
and CH temp before I ever pushed it that extra little bit that blew the
works. I drove 250 miles back home by adding a quart of oil every 35
miles. I lucked out and did not ruin the whole engine.
Stan Wilder
83 Air Cooled Westfalia
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