I replaced the coolant tank on my 87 Vanagon about a year ago.  I  arrived
with a new coolant level sensor.  When I flushed the cooling system  and
replaced tank/sensor combo the low coolant level warning light would blink
until the coolant warmed to operating temperature.  I replaced the low  coolant
sensor control unit and checked the wiring for continuity and excessive
resistance.  There was none.  All of the grounds were cleaned.   Still, the
light continued to blink until the coolant warmed to operating  temperature.
I replaced the female spade connectors on the sensor.   Still, the coolant
light blinked until the coolant warmed to operating  temperature.  By
eliminating all other causes I reasoned that there must be  excessive resistance at
the probes immersed in the coolant.  I further  reasoned that increasing
the surface area of the probe ends would overcome this  increased resistance.
I took two very small gauge spade connectors and cut  off the cylindrical
portion which is intended to be crimped around the  wire.  I took those two
cylinders which were about 1/4" in length and  slipped them over the ends of
the probes making sure that they were just long  enough to cover the probe
ends but did not extend further.  I tightened  them against the probes with a
crimping tool and soldered them to the ends of  the probes.  When I
returned the sensor to the tank and turned the key to  the "on" position the low
coolant indicator light functioned as it was  intended.  It blinked for a few
seconds and then was dark.  It has  continued to function properly for
months.

By increasing the surface area of the probes slightly I was able to
overcome the resistance problem which caused the indicator to continue to  blink.
I checked the condition of the probes recently and found them to be  in
pristine condition.  This was an inexpensive fix for a problem which  defied
solution.

Rico Dagastino
Memphis, TN

In a message dated 2/13/2011 11:32:53 P.M. Central Standard Time,
gfs@GREGORYFSMITH.COM writes:

The past  couple (ok, few) days I've had a blinking coolant light despite
having a  full pressure tank and good level in the reservoir.  Finally
got some  time today and pipetted some coolant form the pressure tank and
removed the  level sensor. Sure enough the probe tips were coated with a
dark  slime.  Wiped it off and all is well.

Gregory Smith
'88 Vanagon  GL

Smith Design Studio
Small Building Company
Olympia,  WA
360-239-0429
gregoryfsmith.com