Expert: Josh Fields - 4/26/2006

Question
i own a 91 318is and i was driving on the highway yesterday and it overheated after about 15 minutes of driving. i saw steam coming out of the radiator and some antifreeze was leaking as well. its never done this before im not really sure what to do. any help you can give would be cool. thanks

Answer
Rob,
 This is bad.  If you got the coolant hot enough to boil and create steam (which is WAY higher than water's boiling point of 212°) and blow hoses off, the engine likely got pretty hot as well.  When engine's get hot, they blow head gaskets, and warp parts of the engine.  

 It's imperative that you keep an eye on the temp gauge,  If you would have noticed the temp guage rising, you could have pulled over before overheating the engine.  So this is a valuable and potentially expensive lesson.

 First off, locate where the leak is... You can go to Autozone and rent a pressure tool for radiators, when you bring it back they give your money back to you (so it's actually free).

 Once you locate the leak we can go from there, hopefully it's in a hose and not somewhere more expensive to fix.  

 I would also try to start the engine again to make sure it's not ruined.  I would fill the coolant tank with water, and then start the engine.  you just want to hear it run, so there's no need to rev it up, or keep it running longer than 1 minute.  You also dont want to run it long becaus you'll have a huge puddle of antifreeze and water under the car.  
 If the engine will not start, then you should have a mechanic take a look at it.

 Hope this helps,
 Josh