It takes a while. When my new engine was just in, we started it up and waited until the fan came on to make sure it worked. I think it took nearly 20 minutes.
The stock temp gauge sits in the same spot over a large range of safe operating temps. If the needle starts to move up to the halfway point or more before the fan comes on, then you can worry.
The stock temp gauge sits in the same spot over a large range of safe operating temps. If the needle starts to move up to the halfway point or more before the fan comes on, then you can worry.