1st 2 times i experienced this was last october my car turned off in the middle of a highway and wouldnt turn back on after 20 min of driving. I took it to my mechanic he said he can't find anything wrong with it he reset the engine light. It's been sitting in my garage for a few month because of snow I took it out yesterday to test it out drove it for an hour it was driving great it didn't turn of but when I got off the high way on a red light it turned off it did this a few times till I got home.
car turns off when it gets hot on 2005 BMW 645Ci
Does your mechanic have the OE GT1 or similar diagnostic computer? Generic code readers won't work on this car. I'd take it to a BMW specialty shop and get a full system scan with a factory computer. I bet there are trouble codes registered in various modules which could help to resolve the problem.
Thanks for your reply Zeetech my mechanic specializes in European cars but I'm not sure what my mechanic is using to read the code but I was trying to avoid BMW dealer but I guess I just have to do it now.