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Date:         Fri, 27 Jul 2001 23:18:44 -0700
Reply-To:     Leon Korkin <korkwood@SURFREE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Leon Korkin <korkwood@SURFREE.COM>
Subject:      Re: Coolant resistance thru coolant level probe
Content-Type: text/plain; charset=koi8-r

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? Why then some people had it blinking with tanks full of coolant? Perhaps the sensor is capacitive? Being more sensitive than resistance? Just guessing. 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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