Nissan Repair: 2001 nissan sentra gxe, nissan sentra, head gasket

Question
I just had my catalytic converter replaced. And all sensors. Not cheap. Now another problem has cropped up just a day later. Possibly related to converter work? On initial start up, and driving on the road, the car is fine. Stopping, then starting the car again after an hour or two, and it runs rough with a bit of steam coming from under the hood.  Head gasket? Hope not! Water pump? Temperature gauge doesn't change, no check engine light either Hoses? Any guess? It's got 172,000 on it, almost all highway, still handles great, with 30-35 mpg. Thanks!!

Answer
Joe,

Steam coming from the engine could be as simple as leaky water pump or hose.  But, a plugged converter can cause a headgasket to blow.  I would have the engine checked for exhaust gas in the anti freeze.  There is a liquid and bellows that they use to draw air from the radiator to check for exhaust gas.  Now, if the leak is small you could use a stop leak in the radiator.