Palindrome-inize a number
A few notes:


A more pythonic way to determine if a given value is a palindrome:

str(n) == str(n)[::-1]


You do something similar in your code, but are converting from a string back to an int.  This is more readable to me.  

However, this can slow down the code if we do this sort of casting a lot, so it would be better to abstract this functionality to a loop to reduce the number of casts and further increase readablity:

def is_palindrome(num):
    string = str(num)
    return string == string[::-1]

Use the palindrome test as a check with the while loop
In the while loop, use the logic you already have to add on a reversed int:

n += int(str(n)[::-1])

I would make it easier to input a number for the code to use, I did this with argparse.

def get_args():
    parser = argparse.ArgumentParser(description=
        'Generate palindrome from number when added to its reverse')
    parser.add_argument('num', type=int, help='number for palindrome generator')
    return parser.parse_args()

Right now you are writing just a snippet of data to a file, but it is being overwritten every time.  I'd recommend just outputting to stdout with this current method, or changing it so you append to a file instead of overwrite it.  I've gone with the former recommendation in my final code.
For profiling and timing code, it's recommended you use a Python profiler instead of writing code yourself.




Final Code

import argparse


def get_args():
    parser = argparse.ArgumentParser(description=
        'Generate palindrome from number when added to its reverse')
    parser.add_argument('num', type=int, help='number for palindrome generator')
    return parser.parse_args()


def is_palindrome(num):
    string = str(num)
    return string == string[::-1]


def main():
    args = get_args()
    while not is_palindrome(args.num):
        args.num += int(str(args.num)[::-1])

    return args.num


if __name__ == "__main__":
    print(main())


Test run:


$ python test.py 146
787