1999 Ford Taurus When car is hot fuel pump fails

This problem has hounded me for a while now(the end of last summer). It started with driving somewhere, going in for a short period of time, and coming back to a car that wont start. This problem is without a doubt related to hot weather. When the car will not start the fuel pump is not functioning. If I let the car sit (or cool down) for a while it starts as if nothing happened. I did not have a single problem all winter. Now that the weather is warming up the problem has gotten worse. Once the car has been driven for a while when I come to a stop it has died two different times. It will not restart and I cannot hear the fuel pump working. After it sits for a while it starts right up. My mechanic say the pump pressure reads fine (35-40psi). And some other tests he ran came back fine, but he hasn't been able to look at it when it is malfunctioning. It is supposed to be hot the next couple of days so i'm hoping to get it to malfunction when he can look at it. I read on another forum that someone replaced the coolant temperature sensor and the problem went away. I was wondering if anyone has any ideas(or can confirm the info from the other forum) i can pass on to my mechanic because as of right now we can't figure it out.
Thanks so much,
Cameron