91 Golf problems (overheating)

Hi, i have a 1991 VW Golf with a 1.8 engine. I'm having a major problem
thats been going on for months now. The car starts fine, but after driving
it for about a minimum of 15-20 minutes and shutting it off, it wont start
again until it cools off. This can take anywhere from 30 minutes to 2 hours
to cool off. I've had the starter replaced, which i was told was the
problem, among other things and it still does it. I dont know what else
could be left. It gives me no indication that it is overheating, and the
temp gauge always goes up to the same point. No smoking or anything. Any
advice on what could further be the problem?? Thanks for any help!

Russ