Have had a chance to use the block heater overnight on the 7.3 while in RV parks with hookups. Pretty nice. Scan gauge Oil temp reads 90 deg F in the morning. Temp drops to mid 80's after starting as the coolant starts to flow. This is with 7 deg F overnight lows. When that warm, usually idle for a couple of minutes before driving easily as temp warms up.
When starting from cold l usually try to get about 5 mins of warm up. Limiting factor is 1der Girl not liking the smell of diesel exhaust. If the breeze is blowing in the right direction all is good!
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com