Mine did the same thing and it was the temperature gauge itself. dbeierl
has an excellent explanation and test procedure here:

http://www.thesamba.com/vw/forum/viewtopic.php?t=353678&postdays=0&postorder=asc&highlight=img+http+images.thesamba.com+vw+gallery+pix+1376779.jpg+img&start=0

On Sat, Feb 18, 2017 at 6:08 PM, Jim Felder <jim.felder@gmail.com> wrote:

> I've recently had my share of problems with a blinking coolant light. I
> have done everything I could think of to do:
>
> 1. New pressure cap (but it's Meyle brand, so a better one is next)
> 2. Replaced the gauge with a re-capacitored one David B did for me years
> ago
> 3. Cleaned all the terminals and finessed the connectors on the foil.
> 4. Made sure grounds were in fact grounds.
> 5. Made sure the coolant was as full as possible, and was mixed properly.
>
> It would not stop blinking at some point on a trip as short as three of
> four miles. I ended up jumping the connector so that the light will at
> least stay off, and it does. I have all new hoses and tank, and no other
> leaks so I am not worried about the coolant going low on me.
>
> Any ideas as to where to look next? Before I jumped the connector, it would
> usually--but not always--start off without blinking, but after a few miles
> it would begin. I have pulled over to check the coolant a lot and never
> found it low.
>
> Jim
>