Ok, trying to figure out my wifes 95 Civic cooling problems. It's a D15B7 engine. First off, it has a new radiator, new thermostat, new coolant, water pump and timing belt are at ~50k miles. Engine has 145k on it.
After prolonged highway driving (45 min at >60mph) the temp gauge will start to rise, and will rise and fall, rise and fall like the coolant is not circulating, this will not happen unless it is subjected to a period of long highway driving, and then the car has to be driven slowly in town otherwise it won't happen, it stays nice and cool at high speed.... So I bled the cooling system, there were tons of air bubbles in the system (obviously the problem) after bleeding it did it again. Bled the system again, after 45 min of driving the overflow tank was FULL and there were lots of bubbles coming into the overflow tank. It took about an hour to bleed all the bubbles out of the radiator when I did it. So I'm thinking maybe I have a blown head gasket, but there are no other signs. There is no white smoke from the exhaust, no radiator fluid in the oil (just changed it to see), and the radiator fluid is nice and clear/green so I don't see any signs of oil in it. Any ideas???