It's the old addage: If you don't inspect it something will be wrong, if you do inspect it, it will probably be okay.
When I start my motors on the hose to flush, it takes a good 15 seconds before I have water running out the exhaust tips. Same thing when the boat is in the water.
My starboard motor runs about 10/12 degrees hotter than the port motor. Has been like this since I bought the boat. I confirmed this by the old "stick the hand in the water coming out the tips" test. It is slightly hotter. So it's not the guage or sender. Gusman says probably different therostat. It hasn't over heated, just runs a little warmer.