Let's face it - Russia's cold.

Actually, Russia's very, very cold. During the winters of WWII, the temperatures on the eastern front reached -20 to -40 degrees. While the Soviets had their own share of problems in this weather, the unprepared German tank forces were forced to light fires underneath their tanks just to thaw out the engine fluids. Multiply the fires by the number of tanks that needed to be warmed up every day and you get one heck of a lot of fires. And every stick of wood used to light those fires wasn't a stick of wood that would be burned to give warmth to the German ground troops, who were freezing to death at an alarming rate.

The water coolent exchange port was a solution to this problem. The water coolent exchange port allowed for the transfer of liquid coolent from a tank which had already been thawed to one that hadn't. The hot coolent would thaw out the second tank's engine and the process would be repeated. With only one fire, an entire Panzer division could theoretically be brought to life in the dead of winter.

WHERE TO LOOK FOR THE WATER COOLENT EXCHANGE PORT

Check the back of German tanks for a panel that includes a small opening for the coolent exchange hose, which transferred the hot coolent from one tank to another.