So I was driving down I-5 and I stop in traffic. well I am looking off into space while I am at a dead stop on the damn freeway when I look down and notice my temp gauge start rising. I was in the left hand lane so I pulled off and shut it down immediatley before it could even get to 3/4 towards hot on the gauge. Pop the hood and my radiatior fluid was waay low. so i started to open the cap just tell it sucked the coolant out of the resiviour to fill my radiator back up. Next day it lost some coolant again, it was a little low when i checked it. Next day I pressure tested it and put 20psi in there and it held fine. no leaks, nothing. since then it has been a week. no leaks and my fluid has been staying full. At first I thought it might be my head gasket. But since the pressure test, it has held all fluid. Maybe it was a fluke and there just wasn't enough added last time I changed the fluid out. Any ideas of what it might be or have been?

 

Airbubble got in there some how? Maybe you fan switch is getting a little twitchy and didn't engage that one time whilst sitting in traffic? I am kinda clueless also but if it doesn't do it again I wouldn't worry about it too much. Just maybe drive around with some premixed antifreeze in your trunk from now on.

Cheers and good luck.