I relay this after my first bout of frozen diesel car while suffering 103-104 degree fever this weekend. I may have come to my senses sooner without the fever...
This is only if the car can't budge from where it sits, usually outside in the cold, and it needs to be started and won't due to extreme cold weather. This is also for those who do not have a garage....After fiddling all day Saturday to no avail, I decided to make a retreat and resorted to a quartz shop light (one of those yellow ones that radiates a lot of heat and comes with protective cage and heavy duty case for burn protection.)
I made use of a foil covered windshield sunshade blanket that's worthless because it won't hold up its shape and draped it over the engine compartment with the foil side facing down then closed the hood.
The shop light was placed under the car so the radiant heat would rise up near the injection pump and fuel filter side of the engine.
Under the shop light I placed an aluminum foil covered cardboard piece for relecting heat upwards and to protect the light from any moisture off the ground.
Went to sleep, woke up this morning and the car started right up.
The quartz shop light didn't overheat anything and the fuel filter, injection pump felt cool but not freezing cold.
Since the quartz light is rated for outdoor use only I felt comfortable leaving it on all night outside and the case design radiates heat at about the same angle as the light with the heat rising upwards and trapped by the foil blanket.
Hope this helps anyone who wants to give it a try if the car is at home and have no block heater.
(I did use a 100' 12 gauge extension cord to reach the car in the yard. Don't use wimpy cords.)
I like this better since the heat source is removed from the engine compartment and under the car to make it more thermally efficient. And probably is a lot safer then some other methods that was suggested to me, such as a space heater under the car...

(I do recall from my overseas years my grandfather wielding a torch made of rolled up newspaper and waving it under his tiny Mazda three wheeler wagon. That did the job for him without failing.)