I think the idle-down period is necessary after extended high-speed (75 MPH
+) heats up the heads.  Higher revs = more frequent combustion = higher
amount of heat energy to dissipate.  The coolant flows quickly and exchanges
the heat efficiently, at the radiator end,  keeping your water temps down.
When you shut down the engine immediately the engine experiences what's
referred to as 'heat soak' -- the coolant over the heads is no longer
circulating and it begins to expand rapidly as it approaches boiling.  This
increases the pressure and pushes the coolant out into the overflow bottle
which eventually overflows.

You would not necessarily experience this condition in city driving because
you head temps stay lower.  You water temps read higher because of lower
engine revs, slower spinning water pump, and decreased air movement over the
radiator.  So, lower coolant temps at the sensor do not necessarily mean
lower head temps or lower oil temps.  In-town driving is harsher than
highway driving, to a point, because of the constant rev changes and lower
oil pressures while idling -- the engine cooling and oiling system do not
operate at peak efficiency.

So, in highway-driving scenario the heat is not distributed very evenly.  In
town the heat is distributed more evenly because of a less-efficient cooling
system, hence the higher water temp readings.

Does anyone have a head-temp sensor on their WBX motor?

----- Original Message -----
From: (Donna Cassano) <pokeswagon@blazenet.net>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, August 15, 2000 4:05 PM
Subject: idle before shut down [was wasserbox]

> Mark Dorm wrote:
>
> >
> >
> > Isn't city driving the hardest with all its stop and go traffic??? ----
>
> That's when my temp gauge starts to climb.
>
> > How many of you have been idleminuteing?
>
> Never have. Might have to try it.
>
> > >The manual specifies that after hard running you must let the engine
idle
> > >for a minute before shutting down.
>
> Boy, who'd a thunk it? What other little "tips" does VW offer in their
manual?
>
> Peace - donna
> '84 Westy (Pepe)