The title kind of says it all. I started up my 83 GSL for the first time in a couple years and ran it for about 2 or 3 minutes (shut it off sooner than I wanted because I was paranoid about overheating it). It was running surprisingly well even for the cold weather with the carb choked part way.
When I opened the radiator cap to add more coolant (thinking that the thermostat may have started to open at that point, the radiator sprayed water about 2 or 3 feet out of the overflow tube, and out from under the cap. What made it even weirder was that the water was still cold.
This scared me and so I shut off the engine because I didn't know what was going on and didn't want to risk overheating my engine.
Has anyone experienced this before? Does anyone have an idea what this could be? HELP!?!?

 

Sounds normal for any engine to me. 2-3 minutes isn't enough for the thermostat to open, it usually takes about 15mins to open, maybe more if it's just idling in cold weather. Since the thermostat isn't open yet, the coolant isn't flowing much at all, the warm coolant stays in the engine and the whole system starts building pressure. When you take the cap off you release that pressure and you get a coolant fountain unless you remove it VERY slowly

Top off the coolant, usually takes 1-2 cycles of filling, warm up until thermostat opens, cool down, fill again and repeat until the coolant level doesn't drop when it cools back down. If it's bubbling through the cap into the overflow bottle when it's warming up then you might have a problem. Wait for it to cool down and take the cap off, then start it back up, if there's bubbles coming up then your coolant seals in the engine are leaking and overpressurizing the system.

 

Cool! I'm glad to hear that I'm not about to kill my engine. I had never experienced that before and it was rather disconcerting. Thank you.

 

So that didn't work as it turns out. Thermostat was busted and never opened. I shut off the engine in time but I almost boiled my coolant.

 

Are you sure you dont have a bad water seal? One of the symptoms is that it will pressurize the cooling system and force a steam of water out the overflow (even went cold).