From my BX manual. Seems I am not far off the mark, for winter use....I might be a little bit agressive for the summer. Although I am sure it's correct for some situations and tractors, there's no way in HE-double-hockey-sticks I have the patience to wait >30minutes as someone else posted.
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I've owned a couple older VW diesels (apples/oranges) and grew very impatient waiting for the thing to blow heat in the dead of winter. Best idea I ever had was a coolant heater on a timer. I'd come out at 7am, windshield would be thawed out in most cases and I had a small amount of heat once I started driving.
I know it's different, but a block heater is not a bad thing at all.