Some weeks ago somebody posted a story of a Golf that overheated and seemed to always be airlocked. Well, It happened to me this week.
Story: day 1: low coolant light in the morning. was ok day before so I ignored it (had no coolant to refill it and had just purged and replaced it and did not want to contaminate if with tap water.)
day 2: needle goes half a line over the 90deg mark, which never does. 2 miles and the heater core exploded. Fogged windshield. Turned A/C on and pressed on (very busy highway). Car did not overheat (never got over 100) until I reached city traffic. Refilled with tap water, and left the cap loose until destination.
day 3: (a week later with the heater core replaced). Tried for hours to refill the cooling system. Always boiled over before the fans came on. Hotwired the fans on and drove it for a couple of days with no problems.
day 4: (2 weeks after day 1) car overheated in traffic and boiled over. Replaced fan switch and still got no fans.
day 5: drained whole system and filled every hose with tap water, making SURE no air was inside. Still got no fans before boiled over.
day 6: Started over refiling and testing every hose for heat. Suspecting a bad water pump I ran for 10 seconds with open hoses, got decent flow. Only cold hose was the bottom rad hose and the tiny hose going from the reservoir to the head.... hmmmm that used to be hot. Took it out and was clogged with a mixture of rust and hose debris. Port into head was also clogged. Succeded in unclogging it partially... started the engine with that hose connected to the reservoir and plugged, not connected to the head. a trickle of water and vapor came out of the hose for 5 minutes and then the fans came on. The bottom rad hose was hot and the system unlocked.
So... I have one or two questions for you: is that port a one way valve or a measured port? Should more than a trickle come out of there? If it should, any ideas on how to unclogg it without taking the head out and hot tanking it? I promise never again refiling it with tap water :)