[Vwdiesel] Runaway 1.5NA Golf

[Mike Dwyer]

Hi All,
 
This is my first post to the list - from Adelaide Australia.
 
I am the proud owner of two 1979 VW Golf GLD - 1.5NA 5 door hatchbacks -
most of you would know them as Rabbits. These are somewhat rare in Oz as
back in the late 70s/early 80s VW was having a hard time selling
anything here due to import duties and exchange rates pricing them out
of their market segment. In fact VW pulled out of Australia in 1980
totally and didn't return until the early 90s.
 
Consequently we missed out on all the neat A2s. In fact diesels were not
sold here from 1980 until the release of the new mark 5 Golf this year!
(Actually about 40 A3 turbo diesels were sold in the late 90s but were
not popular and were dropped).
 
I have completely restored one of my A1s- I am currently waiting for it
to be returned from the paint shop. I will post pics once I get it back.
 
The other I have been using as my daily driver and intended restoring it
when the other is done - and now to the problem............
 
The car has been running very well and starting first pop every time.
Not burning any oil or using coolant. Ran perfectly on a 750km trip from
Melbourne to Adelaide - 52MPG (imperial).
 
Then yesterday whilst cruising at 100km/h on the highway - the car
suddenly went to full acceleration (as if I had flattened the
accelerator to the floor). Backing off the pedal had no effect -
switching off the ignition key also to no effect.
 
Clouds of dense black smoke out exhaust.
 
Luckily I managed to avoid other traffic and pull off into the emergency
lane and stall the engine. Now it turns over but will not start.
 
There is also some evidence of oil in the coolant expansion tank. Not
much, but definitely some...........
 
At a guess the head gasket is toast but I'm new at this......looks like
my first DIY job on a VW Diesel coming up!
 
Is the engine likely to have permanent damage anywhere?
 
What would be the likely cause of the engine "running away" whilst
cruising with absolutely no warning?
 
Any suggestions gratefully accepted!!
 
Regards,
Mike Dwyer
1979 Golf GLD (1.5NA) x2