Date:         Thu, 24 Apr 2008 18:40:43 -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---RESOLVED
In-Reply-To:  <4810FD34.10105@cox.net>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes

Reinstalled the previous thermostat this PM.  I had replaced it
because it seemed to run very cold.

Drove down the highway and back and the coolant temp gauge settled
about middle of the LED and stayed.
Left idling upon return, engine warmed up, radiator fan kicked on for
a couple o' minutes then  cycled off.
Drove down the highway again and needle on gauge returned to center of
LED.

I surmise that this thermo had been fine all along but bad connections
in the engine compartment caused  it to read low on the gauge.
Cleaning these connections allowed gauge to get better information.

Thanks to y'all for listening and for help.

Unca Joel, thanks for the ECU loaner.  I will returned your ECU to you
on Saturday.

Dan

On Apr 24, 2008, at 4:35 PM, Mark Drillock wrote:

> The temp gauge circuit uses the output of the 10 volt dash regulator
> as
> it's power source. (fuel gauge does too) This is so the gauges read
> the
> same regardless of battery condition or alternator voltage output. You
> don't have a problem here.
>
> As the resistance of the temp sensor drops the current flow through it
> increases, lowering the voltage across it.
>
> The plumbing analogy is the more water flows out (current) the less
> pressure remains (voltage).
>
> Mark
>
> Dan Hall wrote:
>> 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
>
>