One other tip: I think a temp of 170 degrees was mentioned in an earlier post. That seems much too high. One thing to check is whether you are seeing any drips with it running in gear and--this part is crucial--confirm that the drips are coming from where the shaft exits the stuffing box. What can happen is that the packing is jammed tight in the nut and there are no drips. Then, a person will loosen the nut until he/she sees some drips. But when you loosen the packing nut enough, you can get drips coming out of the back side of the nut, which will do nothing to cool the shaft. Because of the slope of the shaft, the drips will run downhill and drip toward the aft end of the stuffing box hose, just the same as if the drips were coming out of the front of the packing box (if that makes sense). So you need to look not just for dripping, but make sure that the interface between the shaft and the packing nut, where the shaft exits the nut, shows moisture coming out of it. Even if it's not actually dripping, you should see some glistening of moisture right at that point to let you know it is getting cooling water. If you see that, this means water is cooling the shaft and the temps should reflect that accordingly.
A perfect setting would be a very slight weeping of water when the shaft is rotating and no dripping after the boat has sat for a while and is at rest. (The dripping will not stop immediately after shutting down the engine.) If you have to err, let it drip a bit vs. too tight.