My motor runs cool....maybe too cool?

Once you have verified that your gauge is accurate & your temp is low, then you need to remove the stat & check it. There are some 140* marine stats, pretty rare. Make sure it closes fully.
If you have a high flow stat & the three bars across the top are s/steel [ not brass], you have a Chinese version. I have found that these open at the rated temp, but if the coolant temp drops, they are slow to close. I had a 160 stat after fully opening, didn't close fully till about 130*. Result was engine ran too cool. I now use Stant super stats, open/closes bang on the rated temp.