Occasionally, after driving and turning the engine off, within 2-3 minutes the engine bay starts to smoke and crackle. Popping the hood, its clear that the coolant reservoir is dripping from below and the drops fall directly onto the hot exhaust pipe exiting the engine, thus smoking/smelling/crackling. It last about 5min. During this time, the oil temp reads at max too! The drops are about 2 sec apart. So even after this has happened a few times lasting for a few minutes each time, the overall coolant level does not appear to be low. This has happened only two in the last month, with no correlation to driving intensity, driving time, or outdoor air temperature that I can tell. Seems random. While driving or any other parking I have never seen the oil temp gauge rise above the midpoint. Engine otherwise feels/sounds healthy. I explained the issue to a local mechanical. He "pressure tested" the coolant system to 18 psi or whatever and said there were no leaks or other signs of malfunction. I don't think he probed very hard into the issue. I have not fully inspected the water pump but from the outside I see no signs of leaking. Sounds like some kind of heat soak right? Like the engine can't clear its residual heat after being turned off. But its a mechanical water pump so of course turns off with the engine. Any ideas??