Date:         Thu, 24 Apr 2008 16:03:36 -0500
Reply-To:     Dan Hall <elektro@WESTAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dan Hall <elektro@WESTAL.NET>
Subject:      Re: 86 hot temp gauge---was  '86 Westy cranking trouble
In-Reply-To:  <4810CC73.7010800@cox.net>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes

Borrowed three meat thermometers out of the kitchen drawer and opened
up the expansion tank and stuck 'em in, catching the overflow in a tin
pan.
Van had been sitting overnight, so temp was ambient and not yet
registering on the thermometers.
Voltage on the yellow/red wire from the coolant temp sender shows 9.6
volts.  Should it have shown 12 volts?

Cranked the van and allowed to idle.

The needle on the coolant temp gauge began moving after a couple of
minutes.
  All 3 gauges were in rough agreement, margin of error a degree or
two. after a few mintues. Results below:

Volts                   Gauge                                                   Temperature
8.0                     bottom of big white stripe                                       140 degrees F
7.1                          top of big white stripe                                    158 degrees F
6.2                         center of LED on gauge                                  185 degrees F
5.2                     halfway between LED and top hash
210 degrees F-------1st stage radiator fan came on seconds after I
took the reading. Ran a minute or two then cycled off.
                                     mark on gauge

I'd expected the voltage to rise as the sensor heated and resistance
dropped and needle moved warmer on the gauge.

Or is it that as the resistance drops, more of a load is on the sensor
so voltage drops?

If I am supposed to have 12 volts when I start the van cold, and
voltage drops as engine warms, then does it not stand to reason that
since my voltage is only 9.6 at start up the gauge is not getting
proper voltage throughout the range and thusly is indicating
abnormally high?

Is there a normal operating temperature to look for when driving on
flat/rolling ground with outside air temps in the low 80's(today in
West Alabama)?

And since the brown wire travels over to meet brown wires on the
license plate lite, I wonder if cleaning up those contacts/grounds
might resolve this.

Dan




On Apr 24, 2008, at 1:07 PM, Mark Drillock wrote:

> That brown is always ground. The voltage comes from the yellow/red
> wire
> and the gauge. The gauge measures current flow through the wire and
> sensor. As the sensor heats up it's resistance drops and more current
> flows through it and the wire, so the needle moves higher on the
> gauge.
>
>
> Mark
>
>
>
> Dan Hall wrote:
>> I"ve on the van since 1993.  In all that time, the temp gauge, after
>> warming up would settle in around the center of the LED during
>> highway
>> driving.  Some thermostats would run a needle width warmer, some a
>> needle with cooler.
>> The current situation has the needle 2-3 needle widths past center of
>> LED, almost to where the radiator fan would kick in.  I"ve never seen
>> that before.
>>
>> Will endeavor to get a true temp reading.
>>
>> The coolant temp sender has two wires.  I red/yellow and a brown.
>> On
>> page 97.92 fo Bentley the red/yellow goes to D29 connector on the
>> fuse/relay panel.   The brown connects into the brown wire going to
>> the
>> license plate lite on current track 96, page 97.94 of the Bentley.
>>
>> Can someone tell me how the coolant temp sender operates?  Is it
>> actually getting 12 volts off the license plate circuit and the
>> red/yellow wire sends what voltage it gets through the sensor to
>> the gauge?
>> Or is brown wire always a ground?   And the the gauge is reading
>> continuity to ground?
>>
>> Please forgive my ignorance on the operation of these electrical
>> gizmos.
>>
>> Dan
>>
>>
>