144 Section 1 Introduction to Automotive Technology Copyright Goodheart-Willcox Co., Inc. At the manufacturer’s recommended change inter- val, remove the drain plug. It will be on the bottom of the differential. After draining, reinstall the plug and fill the differential with the proper lubricant. If a drain plug is not provided, a special siphon (suction) gun can be used to draw out the old fluid. Caution Positive-traction, or limited-slip, differentials (both wheels turn for added traction) often require a spe- cial lubricant. Refer to the vehicle identification number and a service manual for details. If you install the wrong lubricant, differential action and traction can be adversely affected. Checking Engine Coolant Engine coolant (mixture of water and antifreeze) is used in an engine’s cooling system. Engine coolant must be changed periodically. After prolonged use, the coolant will deteriorate. It can become very corrosive and filled with rust. This may result in premature water pump, thermostat, and radiator failure. To check the coolant level, look at the side of the plastic overflow tank connected to the radiator. The coolant should be between the hot and cold marks on the side of the tank. See Figure 9-12. When an overflow tank is used, the radiator cap does not need to be removed to check coolant level. However, some older cars do not use an overflow tank. In this case, the radiator cap must be removed to check the coolant level. Warning Never remove a radiator cap while the engine or radiator is hot. Ex- tremely hot coolant can spray out of the radiator, causing serious burns. The coolant should be about 1″ (25 mm) down in the radiator. Also, inspect the condition of the coolant. If rusty, the coolant should be drained and replaced. Watch for system leaks. Checking Power Steering Fluid Power steering fluid level should be checked regu- larly. The engine should not be running when checking power steering fluid. If the fluid is contained in a clear plastic reservoir, simply compare the fluid level to the markings on the side of the reservoir. See Figure 9-13A. In some vehicles, the level is checked by removing a dipstick from the power steering pump, Figure 9-13B. Inspect the fluid level on the dipstick closely. If low, inspect for and correct any leaks. Then add the correct type and amount of power steering fluid. Burned power steering fluid has been overheated from pump wear or a clogged line or passage in the hydraulic system. It will smell like burned rubber. The old fluid must be flushed and replaced. A—Plastic Reservoir Tank B—Clean Funnel Goodheart-Willcox Publisher Figure 9-12. Do not remove the pressure cap when check- ing modern engine cooling systems. Only remove the non- pressurized plastic reservoir cap.