Truck Repair: diesel warmup, moderate climate, cold temps

Question
Mike,
My neighbor has a F-250 diesel. I don't know the year but it has the more square body. He warms it up for 30 minutes every morning. We live in San Francisco and I can only find warm up info for very cold places. What is the proper way to warm up a diesel engine in a moderate climate?
Thanks for any info.
Sue

Answer
This is a interesting question that doesn't come up.  Warming up an engine is, of course a good thing prior to driving.  If your engine operates at 200 deg, then even at 90 outside; the engine is still cold.  I would have to say that 30 min warm-up in San Fran is pretty much a waste of fuel.  I would time it, and see how long it takes to get it up to operating temp.  I would say the time would be more toward 15 min; BUT it is not a "requirement" to have the engine at operating temp before driving.  It all boils down to the owner.  At real cold temps, warming the engine helps to heat up the cylinder temp so the fuel lights better (diesels fire by literally smashing the fuel, and it explodes{for the most part}).  While the engine is warming up it returns unused warmed fuel back to the tank, and inturn helps out even more.   If your neighbor plugs in his truck (block heater) he could reduce the warm up time greatly.  Hope this helps.