x3 on the block heaters!!! Ran them this past weekend when temps only got to low 50's and spent most of the time in the 40's. Plug them in 1st thing in the morning. About 2-3 hours later out of the box at 120 water temp. Car starts easy. Plug them in after the run and very little fuel used to warm up. We made 11 1/8 mile runs and used about 17 gallons of fuel. This is warm up and driven to the lanes and back to the trailer.