Date: Sat, 28 Jul 2001 21:19:49 -0600
Reply-To: Rachel Cogent <Gnarlodious@EARTHLINK.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Rachel Cogent <Gnarlodious@EARTHLINK.NET>
Subject: Re: Coolant resistance thru coolant level probe
In-Reply-To: <3B637EC6.AE92E6DE@charter.net>
Content-type: text/plain; charset="US-ASCII"
I don't get it...
Entity John Rodgers spoke thus:
> All this reminds me of the story of the Ancients who had gathered in
> the front of a barn and engaged in a debate about how many teeth a
> horse had. The debate raged on long into the night, each expressing his
> superior logic and knowledge as to the dental capacity of the horse.
> Intrigued by all this, but intimidated by the presence of the Great
> Ones, the stable boy remained in the shadows, reluctant to disturb the
> debaters. Quietly, he stole out to the horse stall, and gently pulled
> back the lips of the horse and counted the ivory.
>
> That night in the barn loft, as the debaters continued towards the dawn,
> he settled into the straw to sleep. He pulled up his blanket, closed his
> eyes, and a large smile crept across his face.
>
> John Rodgers
> 88 GL Driver
>
>
>
> Larry Alofs wrote:
>>
>> Leon Korkin wrote:
>>
>>> Larry,
>>> That's scientific approach! Valuable results too.
>>> My question is, if trigger point is at 42K than using ordnary tap water will
>>> not cause that blinking light to blink, would it?
>>
>> Right. Although I hope that some other people will try to check the trigger
>> point because my van has been flakey in the past and it is very possible that
>> this value is not typical.
>>
>>> Why then some people had
>>> it blinking with tanks full of coolant?
>>
>> That is the main question. In the past mine has blinked for weeks at a time
>> with the tank completely full of a reasonable mixture, and then healed itself
>> again. David's statement about a marginal capacitor on the circuit in the
>> dash
>> being affected by humidity seems to make sense. I guess I should go into
>> that
>> or learn to ignore the flashing or replace level sensor part with a different
>> circuit.
>>
>>>
>>> Perhaps the sensor is capacitive? Being more sensitive than resistance? Just
>>> guessing.
>>
>> I don't think it could be capacitive. The capacitive between probes that
>> small
>> and that far apart even with liquid between them would be so small that it
>> would
>> be comparable to the capacitance between the two wires leading to the probe
>> or
>> between the wires and any nearby metal. The change in resistance would be
>> much
>> easier to measure.
>>
>>>
>>> Leon
>>> 85 Subwagen Westy
>>>
>>> Larry Alofs wrote:
>>>
>>>> Volks,
>>>> I finally tracked down a coolant leak that had been bothering me for a
>>>> month. Had a small crack in the pressure tank between the pressure cap
>>>> and the coolant level sensor. Since I had to disassemble things anyway,
>>>> I decided to take the coolant level sensor and attempt the definitive
>>>> study of the resistance of various coolant mixtures and then see how
>>>> these values compare to the resistance needed to trigger that &%#*
>>>> blinking light.
>>>> The coolant level sensor was placed in each liquid sample about 1/2 in
>>>> deep in a clean plastic cup. Initially as removed from the van the
>>>> probes looked mostly clean and shiny with a few particles of dirt
>>>> covering less than 20% of the surface. After the first measurement, the
>>>> probes were rinsed between measurements.
>>>> Note that the resistance of liquids generally cannot be measured
>>>> accurately with a typical ohmmeter using a DC test current because
>>>> chemical reactions occur which quickly coat the electrodes and change
>>>> the readings drastically. These measurements were made by using 14 V AC
>>>> applied to a series circuit consisting of the coolant probe and an
>>>> adjustable resistance as a voltage divider. When the voltage at the
>>>> junction was half of the total voltage, I assumed that the adjustable
>>>> resistor had a value matching the resistance of the liquid sample
>>>> between probes of that size and shape. For each sample, I then
>>>> disconnected the circuit and measured the resistance of the adjustable
>>>> resistor using a DVM.
>>>> The coolant from the van only tested to be good to about -10 F with a
>>>> hydrometer,. so it was not the recommended 50/50 mixture.
>>>>
>>>> 1. coolant from van, probes "dirty"------------ 333 ohms
>>>> 2. coolant from van, probes wiped off--------- 356 ohms
>>>> 3. same coolant, probes sanded lightly, rinsed, wiped--- 365 ohms
>>>>
>>>> 4. 100% Prestone extended life (silicate & phosphate free) --- 1667 ohms
>>>>
>>>> 5. 50-50 mixture Prestone & distilled water from grocery store--- 387
>>>> ohms
>>>> 6. Tap water (Chicago)------------------------------------------3603
>>>> ohms
>>>> 7. 50-50 tap water & Prestone ---------------------------------- 384
>>>> ohms
>>>> 8. distilled water, two different brands, same reading
>>>> ------------47000 ohms
>>>>
>>>> Since I wanted to investigate the statements I had read about the wrong
>>>> mixture triggering the coolant level warning, I wanted to see how high
>>>> the resistance had to be to start the light flashing. Got the digiwife
>>>> to sit up front to report on the flashing and reset periodically by
>>>> turning off the ignition. This test was done with the engine not
>>>> running. I adjusted various potentiometers which I had attached to the
>>>> connector for the level sensor probe until I found that the circuit
>>>> triggered at a resistance of about 42000 ohms.
>>>> This circuitry in my van has been acting correctly for the past month
>>>> or so, although it has had bouts of random unexplained flashing over the
>>>> past year (hence the motivation to gather more info).
>>>>
>>>> My conclusion is that most any mixture of water and antifreeze should be
>>>> sufficient to keep the light from flashing, assuming the rest of the
>>>> bizarre circuitry is working.
>>>>
>>>> Whew. Sorry this is so long.
>>>>
>>>> Larry A.
>>>> 91 GL (no coolant leaks and no flashing...today)
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