TM 9-2320 -209-10-1 4-23. OPERATION IN EXTREME HOT WEATHER. WARNING When engine temperature is above 180° F use extreme care in taking off cooling system pressure cap so that you do not get burned/scalded. Turn cap one-half turn to left to relieve pressure before removing. Use a heavy rag or gloves to protect hands. a. General. Continuous operation of truck at high speeds, or under long hard pulls in low gear ratios on steep grades or in soft terrain may cause engine to overheat. Try not to use low gear ratios for long periods, when possible. Always watch for overheating. Stop truck for a cooling-off period whenever necessary and tactical situation permits. If neces- sary, raise hood to help in cooling. b. Cooling System. Scale and rust forms quicker in extremely high temperatures. Always add corrosion-inhibiter compound to cooling liquid. Don’t use water that contains minerals. Fill radiator with rain water whenever possible. Refer to TM 750-651 for engine cleaning compound to be used. (1) Check cooling system often, look for following: (a) Proper coolant level in radiator (refer to TM 9-2320-209-10-2). (b) Leaking hose connections (c) Proper fan belt tension (refer to TM 9-2320-209-10-2). (d) Cracked or leaking hose lines (2) If truck is always overheating inspect and clean radiator fins with compressed air to get rid of sand, dust, and inspect. (3) If engine still overheats tell organizational maintenance. c. Batteries. (1) In very hot zones, check level of electrolyte in battery cells daily. If they are low, add distilled water. If distilled water is not available, use rain or drinking water. Use of water with a high mineral content will damage batteries. NOTE The use of water with high mineral content will do less damage to a battery than letting electrolyte level drop below the plates. A battery left dry has a short life. (2) A battery will discharge faster if left standing for long periods at high tempera- tures. If necessary to park for several days, tell organizational maintenance to take out batteries and store them in a cool place. d. Body and Chassis. In hot, damp climates, corrosion takes place quickly, especially during rainy seasons. Check often for the following: (1) Signs of pitting or paint blistering on metal surfaces. (2) Signs of mildew, mold or fungus on fabrics, rubber and glass. If you find signs of any of these, tell organizational maintenance. 4-408