When using the built in version of navigation you should always do the following:
1. Don't put phone in the window to receive satellites. On a hot day or with the sun beaming into your car this will cause the phone to get too hot. Having the phone sit in a shaded area of the car like on the seat or in a cup holder is better. Or lower where you have your cell phone mount. This will not make a difference in the number of satellites you receive.
2. If you leave the phone on the charger while using navigation you can turn the screen OFF. The nav system will still talk to you and tell you where to turn. This will keep the phone cooler while charging. Once fully charged, unplug from the phone. If you don't do this your phone will get hot. And to imagine some folks are doing this with the phone sitting in direct sunlight. Not a brilliant idea at all.