The last time I posed here was October of last year, after a water pump failure flooded the engine with coolant (I asked for advice on a used engine.) Well, turns out I didn't end up replacing the engine; the mechanic I took it to said the engine looked good and we simply needed to replace the engine parts that had been damaged by coolant. Well, after $6300 and six months at the mechanic I finally took the car back from him for his failure to fix a lingering problem. After returning it to him to repair for the third time, I'm left with a car that makes a grinding noise on startup that goes away after about 2-3 seconds, accompanied by white smoke from the exhaust. What's odd is that this only happens after the car has been sitting for about 24 hours. If I start it more than once in any given day, the grinding/smoke only happens on the first startup. My mechanic could never figure out why this was happening or what to do to fix it, and a Google search isn't very helpful. Any ideas for what could be going on here? I'm not driving it currently for fear that whatever is going on will damage the engine, but I sure would like to have some idea of the problem before I spend more money having another mechanic look at it.