Would running straight water be causing a slightly higher temp?

[LandonL]

I've been running just water in the cooling system just for the motor break-in just to make sure I had no leaks so I wouldn't lose my expensive (to me lol) antifreeze. I was, and AM going to put the antifreeze in it of course but just had this question.

I'm not sure if it's because it's a freshly rebuilt motor, or because I'm running straight up water but the block and parts like intake/valve cover feel hotter than they did before the rebuild.

I'm using a good 180 degree thermostat, the temperature gauge never reads anymore than it did before the rebuild but I'm just running water at the present time, would this cause the block/parts mentioned to feel a tad hotter than normal?

Once again, I'm putting the antifreeze in it, just wanted to know if it was something else that may be causing the abnormal block heat. Other than me being crazy of course and just thinking it's hotter.

Thanks as always!