Overheating

I started having a problem with my small block v8 overheating due to the fan not kicking in like it use to.  I was told that the sender may have lost it's ground, but I checked it and that is not the case.  I changed thermostats and that didn't help. I have a new sender and put in a manual switch.  The old sender is in the head, I was told to move the new one to the front of the intake and keep the sender wire away from the spark plug wires.  The car only has about 400 miles on the breakin.  My temperature gauge goes up to about 230 or 240 before the old sender kicks in the fan,  but no boiling over or over flow.  Can the gauge also be bad now? It is in the right head. I have a 180 deg thermostat and a 185 deg sender. Coul the timing cause the reading to go that high?