I have a receptacle at work and leave my block heater plugged in all day. When I get home I plug it in again. My 85 300SD is pretty much plugged in 24-7 in the winter. I know it may waste energy....but think how much my engine loves me! The instant heat is a nice plus. Never had a problem with the regimen and I've been doing it this way for years. My car loves it!

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Orland Park, IL
1985 300SD 215,000 miles