I had the exact same thing happen with my 82 Buick skylark.

Under load it would overheat, and the wanring light would come on ever so
slowly, blinking quite a bit before actually indicating an overheat
condition.

I drove hundreds of miles like this, and when the hill was too steep, I
would simply pull over and take a break.

Eventually I had to get it repaired, as it was overheating at slight highway
uphill grades, at night, even in the rain... so I knew something was not
happy in there.

When the mechanic in Florida tore it apart, he found a radiator core which
was so gummed up inside by rust and mineral deposits, that there was no way
that enough flow could pass, and that any significant cooling could occur.

I had the then replace the radiator, and drove the car for several thousand
more miles with no overheating issues.

Good luck troubleshooting,

RSF

IMPORTANT!!! In order to reply to me, you must have the word "FISH"
somewhere in the subject line of the email.  Otherwise it goes directly in
the trash.

<�)))>{   <�)))>{   <�)))>{   <�)))>{   <�)))>{   <�)))>{

Robert S. Fish
Salzburg, Austria
1987 Wolfsburg Vanagon 2.1 GL Weekender
1987 Golf Cabriolet
1991 Golf

snipped ---------
cooling
> system just didn't seem to have the cooling capacity to handle heavy
> loads (mountains) or high (80 degree plus) ambient temperatures.
end snipped ----------