what would cause the smell of coolant,when driving, no leaks seem to be evident?

The most common cause of coolant misting and smell through the vents into the cab is a heater core leak. Not sure what you are referring to when you say "Knock Sensor". Are you losing coolant? I know you said you can't find a leak, but if you have to add water and anti freeze to keep the system fully charged, you are losing it somehow. Is your system maintaining pressure and flow? Your temp gage should be reading normal temp for the thermostat you have installed. If you have a 190 degree thermostat and you are running at temps over that amount, you have inadequate flow or volume in the system. That could be a leak, a water pump that is failing, a thermostat that is sticking, your air flow is not adequate or your coolant to water ratio is off. Those possible issues are fairly easy to test for and rule out. The more serious problem would be a head gasket or cracked head. You want to avoid running it hot for this reason.