i wanted to bump an old thread, because this sounds like exactly what i am experiencing. today was the first really hot day in Chi, over 90 degrees. was driving pretty hard all day, in stop and go traffic on the way home. when i got home, i smelled coolant, so i popped the hood and coolant was bubbling out from under the edges of the cap on the radiator, NOT via the overflow hose.

i just topped it off, ran it awhile w/o the cap in case there was any air, though the reservoir was not completely depleted, so i don't think that was needed. kept an eye out for any bubbles forming up in there, didn't see anything.

jumped on the highway and ran the hell outta her for a good 15 minutes

kept my eye on the temp gauge the whole time, didn't budge from the middle. popped the hood when i got in and everything looked good, but when i put my ear close to the overflow cap, i could hear a slight fizzing sound like it was slightly bubbling.

so... is this just a case of a bad radiator cap or does this sound normal? i've never had a radiator cap that wasnt actually on the radiator itself, so this strikes me as kind of strange. i've only had the car since the winter time, so i am guessing it is possible i was slightly overfilled and it just bubbled off, today being the first hot day.

thanks guys