If the needle is pegging over right away I think you have a broken wire to the sensor or a connector that has come loose. 

Jim

On Jul 10, 2013, at 10:52 PM, Dennis Haynes <d23haynes57@HOTMAIL.COM> wrote:

> On that year, low coolant will flash the light and peg the gauge to get your
> attention. So go check the coolant level in the pressure tank while the
> engine is running and the light is on. If it is less than 1/2 full then you
> have a problem with the cooling system. If it is filled to the top you have
> an electrical problem. It is important to check with the engine running. If
> you shut it off the coolant will flow back into the tank and appear full.
> 
> Dennis
> 
> 
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Woody Halsey
> Sent: Wednesday, July 10, 2013 11:01 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: overheating warning light flashes immediately on 83.5 V'go
> 
> I am back on the list after a 2-3 year hiatus, hoping someone has come up
> with a surefire solution to my chronic problem in the interim. I was away
> from the V'gon for a year. Came back to the US. Started her right up w/no
> problem, as a nice neighbor had kept the battery charged and turned her over
> from time to time. BUT I do not dare take her out on the road (I have come
> home on the back of a AAA truck too many times) b/c the temperature gauge
> pegs over and the warning light begins to flash the minute I turn on the
> engine. I cannot believe that the engine is actually overheating.
> 
> Any suggestions will be more than welcome.
> 
> Thanks in advance. Good to be back.
> 
> Woody Halsey
> Haverhill, MA