Mark....
Great Post!

Bill

> As some on the list may remember, there recently was a thread regarding
> a reported difference in behavior of the flashing coolant LED from one
> Vanagon to another in response to a low coolant level. I can now report
> the answer to this mystery. There are 2 (maybe even 3) different
> "coolant level low control units" that control the behavior of the LED
> when a low coolant level condition is detected in the main tank.
>
> The original version is part number   251 919 376.
> The later (85+) version is part number  191 919 376.
>
> Both  versions start flashing the LED about 10 seconds after a low level
> condition is detected but then they have 2 behavioral differences.
>
>         Difference 1.
> The original version flashes but also makes the temp gauge needle rise
> to the very HOT end of the scale.
> The later version flashes the LED but still properly displays the actual
> temp of the engine as sensed by the coolant temp sensor.
>         Difference 2.
> The original stops flashing and resumes normal gauge needle operation
> about 20 seconds after the low level condition is corrected.
> The later version continues flashing after the level is corrected and
> only resets after the ignition key is turned off and back on.
>
> Any year watercooled can have either part number as they interchangeable
> other than the differences noted above. I think the later model is to be
> preferred as I want to know the reason the LED is flashing. The flashing
> LED has 2 meanings. If the engine temp rises high enough it flashes to
> draw your attention to the gauge. If the coolant level in the tank is
> low it flashes to warn you to check it. With the original control unit
> you can't tell which problem you have. I would want the later version so
> I would know if the engine was HOT so I could stop ASAP. If it was only
> indicating a low level but still a normal temp I would know I could wait
> a little while to find a place to stop and check it.
>
> Mike Snow and I tested both of the above parts in a 1983 with a clock
> and large temp gauge in the dash.
> Then we tested both of the same parts again in a 1987 with a tach and
> the smaller temp gauge.
> The behaviors completely followed the control units and the year and
> type of dash did not matter.
>
> There is a 3rd version referred to in the Vanagon parts documentation as
> superseding the others in 1989. It is the later number with a "C"
> added.  191 919 376 C.  We did not have this unit available to check.
>
> Mark
>