Several years ago, I started my Mazda GLC and headed out on a road trip only to find out that the block was frozen. I was not able to get any heat out of the heater and the engine temperature gauge went "through the roof" in only a matter of minutes. I was thus forced to figure out how to unfreeze my car engine; for I knew that if I continued to drive it in that condition, I would ruin it in no time.
I took the car home and put it in the garage, for it is impossible to thaw out a car engine outside in freezing temperatures. In order to thaw out an engine, you have to raise the temperature of the engine block and the hoses for a sufficient period of time so that the ice in the engine will thaw. I rented a large propane heater from the Rent-All store in our community and turned it on in the garage far enough away from the vehicle so that it would not start on fire or melt any of the paint on the vehicle. I proceeded to wait, thinking that it would only take a few minutes, or perhaps an hour or two.
I became very frustrated within a matter of a few hours as I initially met with little success. I opened the door after an hour or so and started the engine hoping that my engine thawing was complete. It was not! The engine immediately overheated again. I began to realize that unfreezing a car engine was going to be a bit harder and more time consuming than I had thought. As I had now lost all the heat in the garage, I had to start over from scratch, for the temperature in the garage was now below freezing again. So, I closed up the garage and proceeded to try again, this time leaving the heater running overnight.
In the morning, I tried again, but was met with similar success. The engine block was still frozen. As I had opened the garage again, I had to restart the process over for the third time. This time I allowed the heater to run for a couple of days; for I now realized that while the garage was heated sufficiently, the temperature of the engine block itself had not risen very much at all.
After a couple of days, I looked in the radiator -- and to my delight, the contents were liquid once again. My engine block had finally been unfrozen, and I was now ready to go. I immediately added sufficient antifreeze to make sure that the engine block would not freeze again as soon as I left the house. I returned the heater to the Rent-All store and paid my bill. My car was now ready to roll.
I learned from this process that in order to unfreeze an engine block, the entire block needs to be warmed thoroughly, and it needs to stay warm for a sufficient period of time so that all the contents of the block can be raised above freezing. While antifreeze will keep water from freezing; once frozen, it needs to be heated to a temperature higher than its protection value in order for it to turn back into liquid again. This takes time and patience. As my garage was uninsulated, much of the heat from the heater simply dissipated or escaped through the roof. This prolonged the process as the heater had to work even harder and longer in order to hold the block at a sufficient temperature for a sufficient period of time so that the engine could thaw.