Flush cooling system, make sure heater core isnt bypassed. Make sure also that coolant level is correct. start engine cold with radiator cap off and watch coolant level. see if it drops when thermostat opens and then add proper coolant. Also be a ...
Electric will be all the heat you need. Just a little longer to heat up than using the Diesel. Use the electric when shore-power is available and diesel when it is not.
