My car came with a 400 Watt true block heater from the factory. The elements are right in the block underneath the head. I find that just 15 minutes of use makes all the difference in the world as far as getting the thing started. I get no white smoke from incomplete diesel combustion and the starter spins the crank much faster. If I leave it on for 30 to 45 minutes I get heat out of my heater a lot quicker. I might mention that I have a 3.0L diesel with a cast iron block and head.
I guess this shows what putting the heat where it matters most can do.
