quattro digest, Vol 1 #4654 - Correction for - Confused about synthetic gear oil-

[Larry C Leung]

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Windchill is a perceived effect based on the cooling rate of
an object that is above the air temperature. Warmer objects
will cool quicker in a higher wind situation than they would
in still air, that is until they reach the actual air temperature.

Since we are humans, whom are (hopefully) above room temp,
we experience the quicker cooling than normal, so we feel as
if the air were colder, thus called the windchill effect. Also note,
a warm shut off engine will cool more rapidly to the air temp
if the wind is sufficiently fast. Thus, windchill is NOT limited
to humans, but could be determined for the car by comparing
the cooling rate in the wind to cooling rate in still air. Find the
still air temp that would cool the engine as rapidly as the windy
air, and that would be the "wind chill" effect for the engine.

The factor was developed (and it is still being refined) using the
cooling of a standard amount of, I think water. I can check and
verify this later if anyone really cares, I'm not near any resources
right now.

BUT, once an object reaches the air temp, that is it, it will cool
no further, still air or not. This is the example of Louis-Alain
Richard's
post, the thermometer was already at air temp, the hand, well....

Now as far as the gear oils, in the tranny, use GL4, which protects
synchros. In the diffs, you may use GL5, whose additives are designed
for such high pressure apps. Different oils for different applications.
GL4 is
NOT OLDER OR NOT AS GOOD as GL5, it is a rating that allows it
to be used in synchromesh transmissions by having the appropriate
friction modifiers. Thus, ANY GL4 gear oil is appropriate for the
gearbox,
and is thus specified in our owners manuals and the Bentleys.

Just to be clear, Mobil 1 GL5 synthetic gear oil IS NOT for the
transmission!
It's great in the diffies, but it will eventually destroy your synchros.
This will
apply to ANY GL5 oil.

BTW, synthetic oils have better flow characteristics when cold than dino
juice. They will have the same viscosities (i.e. fluid shear strength,
which
many would percieve as "thickness") but they will pour better at the same
cold temp, thus shift better when cold.

FINALLY, if you read your owner's manual, at least the later T44 quattro
gearboxes (such as my '89) SPECIFY synthetic gear oil, GL4 variety. It
does NOT specify dino GL4 fluid.

LL - NY



> Reply-To: <larichard at compagnonderoute.ca>
> From: "Louis-Alain Richard" <larichard at compagnonderoute.ca>
> To: "Robert Deutsch" <rdeutsch at sk.sympatico.ca>
> Cc: "Quattro" <quattro at audifans.com>
> Subject: Correction for - Confused about synthetic gear oil-
> Date: Tue, 25 Feb 2003 11:45:43 -0500
>
> Windchill is a factor only for humans; don't use this when talking
> about th=
> ings. A home thermometer will prove this very fast; try sticking it
> through=
>  the side window and accelerate; it will always show the same temp
> no matte=
> r how fast you drive but your hand will feel colder as speed rise.
>
> Louis-Alain
> Born in Sept-Iles PQ, where -40C is also unspectacular.
>
> <SNIP>
> For those who do not know what cold is, here in the province of
> Saskatchewa=
> n, Canada, we
> hit temperatures of -40 C (-40 F) and -55 C (-67 F) with windchill
> this pas=
> t week.
> <SNIP>
>
> Rob Deutsch
> '90 CQ20v
> '01 Beetle Turbo S
>
>
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> End of quattro Digest
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