what a coincidence... I replace the thermostat on my '88 GL yesterday.. I
put in a 80°C thermostat (we live in So. Cal.), I also replace the the
coolant sensor for gauge..

I topped up the main reservoir, test run, top up one more time and all went
well...

if you have problem... this may help..

http://www.benplace.com/bleeding.htm

http://www.vanagonauts.com/By-the-Bentley193.htm