the  stock temp gauge sender is pretty close to the thermostat.
so when that comes off the peg...........
it's starting to close off the bypass circuit flow in the engine, and
starting to send coolant toward the radiator.
And the sender shows the temp of the radiator circuit coolant .........
they'd want to read the hottest coolant as it comes out of the engine.
< shoot, come to think of it........
has anyone ever bothered to figure out if a water boxer thermostat is on the
return side from the radiator , or on the 'feed to the radiator' side. Most
newer engines have the t-stat on the return side to the engine........
like all vw inline fours gas and diesel since the 1975 Rabbit, like Subaru
engines etc.  I never bother to check that out )

The thermostat in a waterboxer engine is  a 'two door' thermostat
........two cirucits ............one is 'bypass'. around and around through
the engine.......
bypassing the radiator circuit. The other circuit is the radiator circuit.
The t-stat switches gradually over from one circuit to the other. The Heater
circuit is something else of course, and not termostated in any way.

That might even take 10 minutes...........as as it blends from the bypass
circuit to the radiator circuit.
so the change over is gradual. My guess is that at 25 % gauge defelction (
halfway from zero reading to mid-defliction, by the LED ) is about half
split between bybass circuit, and radiator circuit.

You won't see 'full thermostated' temp at the radiator until after it's been
in the radiator only portion for a short while. Like fully up to temp, plus
a few more minutes, depending on rpm ( water pump speed ) .  In town at
lower speeds, lower load, it takes longer to get fully up to temp. Sometimes
it won't even get up to full temp, in town, at low load and rpm ......even
with a good new german t-stat IF ..........
you have the heater on from the begging ( a bad thing in cold temps ) and
it's very cold.

the best deal is a new german, OE quaility thermostat in the higher of two
temps offered. Warmer is better, cooler is not.
And shortish in town trips in very cold temps..............is really rough
on a waterboxer.
It would bee worth it to cruise out of town on the highway for 5 miles, turn
around, then go about your town errands, in very cold temps.........like 20
degrees F and below.
I just pulled this inline 110Volt AC 'house power' electric heater out of a
parts van of mine. I gotta put that in my heater circuit of my van and plug
it in overnight while it's still cold. Sure would be nice if the engine
coolant was partially warmed up, and all the coolant in the heater circuit
was already warm, soon as I start 'er up !

scott
www.turbovans.com

----- Original Message -----
From: "neil N" <musomuso@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, March 11, 2009 1:57 PM
Subject: Re: Takes a darn long time for the heater to come up to speed

> On Wed, Mar 11, 2009 at 1:35 PM, Rocket J Squirrel
> <camping.elliott@gmail.com> wrote:
>> What's the easy way to tell whether the thermostat stays properly shut
>> until the engine reaches temperature? I was thinking of starting the
>> engine, take the temp of the radiator with an infrared thermometer,
>> watching the temp gauge, and, according to my theory, when the gauge
>> starts to indicate operating temperature the radiator should suddenly
>> start warming up. That should work, right?
>>
>>
>
>
> Short of removing the thermostat, boiling it in a pot of water and
> watching/measuring with a thermometer, I would suggest aiming your IR
> gun at the thermostat housing. See when the temp goes up there.
>
> I would imaging that measuring at the rad would take longer.
>
> Neil.
>
>
> --
> Neil Nicholson '81 VanaJetta 2.0 "Jaco"
>
> http://tubaneil.googlepages.com/
>
> http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines