1 time coolant boil over. Please Help

[Divinehammer]

my car was running really hot and I am not sure why. about two weeks ago I added some coolant and water to the system to bring it up to above the full line. I did not notice any problems after doing this. Today I went about 10 or 15 miles kind of driving hard but not really just city driving still not a problem then I made a run to the gas station 1 mile and came back home parked in the drive way on an incline the vent was still blowing but no AC I was setting the radio so after about 20 mins I look at the ground and all of this coolant isrunning out under the car, so I pulled it in level and then opened the hood the coolant resevoir was all the way full and coolant was leaking out of the overflow tube down the car and on the ground. so I let it set and the level dropped to just above full. So I let it set for the afternoon. then this evening after a short run the coolant that had dripped out earlier was smoking I assume from contacting something hot, but this time I noticed that the temp gauge was all the way to the top not a good thing so I shut it down and let it set to cool down. coolant was still above the full line and drops after it cools I assume that is natural other than a few drips there is not alot of coolant on the floor so I dont think that it is a leak but I am not for sure. I took some of the coolant out so that it was between the low and full line, restarted and it ran correct about in the middle on the temp guage. and coolant did not really change. I only let it run for a few minutes though. The system has never been flushed and it has 77k miles. I have not driven it since it ran hot. Please point me to some good instructions if I need to try something, I am certainly no mechanic. Or instructions on how to flush this myself. Thanks for the help.

 

[evilmonkeyMSP]

perhaps you just overfilled it?

 

[speedprotegewi]

1st thing, flush your coolant every 30k miles not every 77k. 2nd, did u fill the overflow when it was hot or cold? if u filled it to full when cold yes it will most likely overflow because the level raises when hot. technically the low level can also be called cold level, and the full is the hot level. if it hasnt done anything since then i wouldnt worry about it, but if temp is rising regularly, it could be due to needing a coolant flush, bad t-stat, or in extreme cases head gasket

 

[Divinehammer]

well turns out that it was a sluggish thermostat because it was intermittent started it up and went around the block temp was fine headed to get it flushed and temp went hi but not to the top and then all of the sudden dropped to normal temp. replaced thermostat and flushed radiator. I am no car guru but Iam learning thanks for the replies.