Date: Thu, 24 Apr 2008 14:33:59 -0700
Reply-To: Mark Drillock <drillock@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Drillock <drillock@EARTHLINK.NET>
Subject: Re: 86 hot temp gauge---was '86 Westy cranking trouble
In-Reply-To: <C6E5C392-4295-4659-87F8-7AF0723F5BE9@westal.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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
>
>
>
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