The factory stock block heater in my 2000 K3500 Detroit 6.5 would warm it fast enough to feel slightly warm air in just a couple of hours after plugging it in. I mostly just planned on when to use the truck and rarely left it plugged in overnight, never failed to start.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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