Date:         Fri, 28 Jun 2002 20:32:03 EDT
Reply-To:     FrankGRUN@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Frank Grunthaner <FrankGRUN@AOL.COM>
Subject:      On Gauges, oil coolers and Stan's jaundiced view
Comments: To: wilden1@JUNO.COM
Content-Type: text/plain; charset="US-ASCII"

In a message dated 6/28/02 12:57:21 PM, wilden1@JUNO.COM writes:

<< I've had the VDO after market gauges and a set from an Audi 5000 GT
coupe.
Besides the faces falling off all of them I'd say they are all just
generically sorry.
Gauges are for monitoring and after a little 12v tweaking with a constant
voltage diode i'm satisfied that I can drive in a safe but wide spectrum
of temperatures.
The oil pressure gauge is right on but I can't help but wonder why every
other oil gauge I've ever had swings the needle slowly and the VDO
needles race. >>

Just can't let Stan's curmudgeonoid attack on VDO gauges go unanswered.
Obligation to the youthful and impressionable listees. Of course and
regrettably he's correct that the accuracy of VDO gauges (and any affordable
substitute) is extremely wanting. The precision, however is outstanding. In
this world of affordable, unreliable motoring, good precision is more than
adequate. In point of fact, the indicated temperature will be effected by the
resistance of the path from gauge head to sender, through sender and on to
ground. With moderate care during installation (adequate wire gauge, clean
contacts, sealed contact points) the VDO gauge will reproduce its measurement
of a given temperature within +/- 2 degrees F. The point is that after the
gauge install, you will soon learn the normal range of operation and changes
alert you to problems. If Hubert Listee says that his normal operating
temperature is 90 degrees C, and yours appears to be 80, its probably not
important. But if he sees a change of 20 degrees, then for the same mod, you
should see the same.

Of course a real gaugaholic will calibrate his sensor system to know the
offset between truth and measurement. Stans candy thermometer probably
relates to a poor relationship with his significant other (SWMBO has several
times suggested that her caramel sauces had a certain aliphatic hydrocarbon
flavor - but I had rinsed the GD thing in Brake cleaner several times!) but
it is only a secondary standard. Boiling ASTM type 1 water, pyrex surfaces,
deoxygenated at sea level - 100 C. Of course you all knew that. Generally if
you calibrate at two points, you will find that only an offset is needed to
approach truth.

Now, all reputable gauge makers understand the atrocious variation in voltage
in the automotive electrical system. They will all build in a Zener diode or
equivalent voltage regulator into the input circuit of the gauge. Most
automotive gauges will be regulated to a point between 5 and 10 volts. If the
gauge value dips below this control value, it will go unstable. So Stan's
observations of gauge wiggle with load testify to bad connections such that
the available voltage has dropped below reasonable values (read this as going
below Ford, GM, Chrysler, even Subie voltage performance levels and down to
Vanagon levels). As I have said before, I balanced the refrigerator/stove
mass with 00 gauge wire running from rear to front!

Oh well, back to the Cointreau!

Frank Grunthaner