TECH - Coolant Level Warning Circuit

[pbureau@attbi.com (ATS - Patrick Bureau)]

I would like to add that this only applies to 16v engine, as no 8v engine
has a sensor on the coolant tank.
it is actually located on the oil flange :)

-------------------------------------------------------
    __  __________
   /  |/_ __/ ___/ Patrick Bureau
  //| | / / \__ \  1985 8v Prowler Orange "Beatrice"
 / _  |/ / ___/ /  1985 8v Titian Red "Lucky"
/_/ |_/_/ /____/   http://www.longcoeur.com/scirocco

=>-----Original Message-----
=>From: scirocco-l-admin@scirocco.org
=>[mailto:scirocco-l-admin@scirocco.org]On Behalf Of John Erickson
=>Sent: Thursday, August 22, 2002 12:21 PM
=>To: scirocco-l@scirocco.org
=>Subject: TECH - Coolant Level Warning Circuit
=>
=>
=>Flashing Low Coolant Light Circuit Description.
=>
=>The trigger for the warning circuit is the sensor in the
=>top of the coolant expansion tank.  Make sure you have the
=>proper level of coolant and the electrical connection on
=>top is clean.  Assuming that there is electrical
=>continuity everywhere in the circuit (no broken wires or
=>dirty electrical connections), there can only be two
=>things that cause the light to flash when there is the
=>proper amount of coolant in the expansion tank: a faulty
=>sensor and/or relay.
=>
=>If you look at the sensor, it consists of two small metal
=>rods (probes) that extend into the coolant.  If current
=>can't pass between the probes (low coolant condition),
=>then the relay will activate the warning light in the
=>temperature gauge.  I really don’t know how the sensor
=>could fail, but perhaps if the cooling system was
=>neglected for a very long time, corrosion might be an
=>issue or perhaps there might be a build up of crud on the
=>probes inhibiting current flow.  You can remove the sensor
=>and clean off the probes.  You can also test it via a
=>simple continuity check (probe-to-connector).  New sensors
=>cost US$10.
=>
=>The relay is in position #18: third row (top) far right
=>hand side. There is a "43" on the old relays (new ones are
=>blank).  Its only function is to pass current through the
=>sensor and to trigger the light if it can't.  Its not a
=>standard electro-mechanical relay, by the way.  You cannot
=>take it apart and clean any contacts.  It has a small
=>printed circuit board inside with some sort of silicone
=>device (chip) on it, a few resistors and perhaps a diode
=>or two.  I'm pretty sure its an electronic relay, but it
=>may be slightly more complicated than that.  If you remove
=>the relay, you will still get the flashing coolant level
=>light when you start the car.  That's a bulb test function
=>not associated with the relay or the sensor.  New relays
=>cost US$30.
=>
=>Continuity issues:  Before you start replacing parts,
=>clean the relay contacts and the connector on the sensor.
=>  The connector on the sensor is terribly susceptible to
=>corrosion due occasional baths in coolant.  The connection
=>also tends to get loose from frequent use.  If you spend
=>much time in that corner of the engine compartment, the
=>expansion tank gets moved a lot.  As a result, the
=>connector gets yanked a lot.
=>
=>There is very little information about the low coolant
=>warning light in the Bentley manual.  The circuit is not
=>covered in the electrical schematics.  I found the relay
=>in the manual, but, according to the book, my car doesn't
=>have one.  It's called the "low coolant indicator/idle
=>boost control relay."  Perhaps on some cars it's the low
=>coolant indicator relay and on others it's the idle boost
=>control relay.
=>
=>
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