| Cooling System Overview and Routine Maintenance |
From "Car Care & Repair"
episode CCR-109 |
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Your car's cooling system is designed to dissipate the thermal energy generated by several thermodynamic processes that occur inside your engine compartment. In other words, the cooling system keeps your engine from burning itself up. It does this by keeping a liquid coolant (a mixture of water and antifreeze) circulating through your engine block and through the air-cooled radiator that disperses heat to the surrounding environment. When something malfunctions within the cooling system -- a clogged radiator, a hose leak, a worn-out thermostat, a broken water pump or a damaged heater core, to name a few possibilities -- your engine is certain to get too hot for its own good. Following some preventive maintenance guidelines, and being informed of how the cooling system operates, may help keep you from experiencing the inconvenience and frustration of being stranded because of an overheated vehicle. Be mindful of the early signs that may be telling you that your engine is overheating . An overheated engine is one of the most common causes of roadside breakdowns. Don't ignore signs such as a hissing sound (indicating steam escaping) or small amounts of visible steam rising from beneath the hood. Likewise, don't ignore a "hot" smell or an odor of antifreeze. Observe where the needle on your dashboard temp gauge normally rests when the engine is running and in good working order. Check your temperature gauge periodically, especially on long trips. Immediate steps you can take if your engine is running hot. If it's in the summer, turn your air conditioner off. The air conditioner can make your engine run about 20 percent hotter than it would otherwise. Also, increase your following distance from any vehicles in front of you so that you're not exacerbating the problem with the heat radiating from another vehicle. If the engine continues to run hot, it may help to actually turn the heater in your passenger compartment on with the thermostat set on its highest setting (figure A) and with the fan running full-force. Since the vehicle's heater draws energy from the engine-cooling system, running the heater with your windows rolled down will help to further disperse excess heat. If your temperature gauge reaches the red zone, or your temperature warning light comes on, pull off the road to let the engine cool, and identify the problem or seek assistance. Continuing to drive with a severely overheated engine may cause irreparable damage. The operation of the cooling system. Since your engine utilizes internal combustion for power and generates friction when internal surfaces rub against one another, it is capable of generating massive amounts of heat. To disperse that heat, liquid coolant is circulated through the engine block where it exits via the upper radiator hose. The coolant then enters the radiator and flows through a network of thin-walled fins and is air-cooled by the air flowing through the front grill when the vehicle is in motion. The ability of air to pass through the network of fins can be illustrated by shining a bright light behind the radiator. Just as the light can be seen to pass through the fins (figure B), moving air, augmented by the radiator fan, passes through and cools the contents of the radiator (figure C). By the time the coolant has reached the bottom of the radiator, much of the heat has dissipated. The cooled liquid is then pumped back into the engine block by means of the water pump (figure D). The flow and temperature of the coolant is regulated by means of an electronic thermostat. An ancillary benefit to this process is the ability to make use of the dispersing heat to warm the passenger compartment of the vehicle. With the inside heater engaged, the warmed coolant circulates through the heater core and warms the surrounding air. The warmed air is circulated into the passenger compartment by means of a fan. Many of the problems that can arise with the cooling system are maintenance-related and can be avoided if certain factors are monitored regularly. Take steps to avoid developing a clogged radiator. The inside of a radiator can become clogged with a buildup of sediment and deposits if the radiator isn't flushed and serviced regularly. Note the condition of the openings inside an older, clogged radiator (figure E, left) in contrast to those in a newer one that has been well maintained (figure E, right). This type of buildup impedes the free flow of coolant through the system and reduces cooling efficiency. Back-flushing your radiator and changing your coolant annually will reduce the likelihood that this condition will arise. Check the condition of your coolant. The antifreeze component of your coolant solution prevents the coolant from freezing during extremely cold temperatures -- a condition that could crack and permanently damage the engine block. New antifreeze has a bright yellow-green appearance with a distinctive iridescent sheen. Older antifreeze will take on a darker, brownish or rust-colored appearance (figure F) that may indicate the presence of rust inside the body of the radiator. Older antifreeze that has begun to darken has likely lost some of its effectiveness. It's easy to test your antifreeze with a hydrometer. Simply squeeze the bulb and draw a sample of antifreeze up into the clear-plastic test compartment of the gauge. The position of the needle inside the compartment will indicate the temperature to which that coolant will safely maintain its effectiveness (figure G). Pressure-test your radiator cap. Your vehicle's cooling system is a pressurized system. This is because the boiling point of most liquids is higher when under pressure. Therefore a pressurized system can effectively operate at higher temperatures before the coolant would begin to boil over and turn to steam. Because the system is pressurized, all of its components -- including radiator housing, hoses and gaskets -- must be strong enough to withstand pressure within a normal operating range. One of the components that can become a weak link is the gasket at the bottom of the radiator cap (figure H). Radiator caps are pressure-rated to indicate the amount of pressure they can safely withstand. The rating is generally stamped on the top of the cap. You can test your cap to make certain that the gasket is continuing to hold up under pressurized conditions by use of a pressure tester (figure I). With a cool engine, simply remove the radiator cap and attach it to the tester. Then hand-pump the tester to capacity and check the needle to see whether the cap is holding pressure to its rated specification. Check the condition of all cooling-system hoses and hose-clamps. Much like the gaskets in the radiator cap, the hoses in your cooling system can weaken over time and rupture when heat and pressure reach a certain point. Through wear and age, they may also develop splits (figure J), cracks or frayed ends, or they may become worn because of accidental contact with some moving part (figure K). A periodic careful inspection of all the hoses in your cooling, as well as the clamps that hold them attached, will help you identify trouble-spots before a system breakdown occurs. Tip: When it's time to replace a hose because it has become old and worn-out, ideally this is a good time to go ahead and replace all of the hoses in the system as a set. Replacing one "link" in the system so that it's new and strong, while leaving the remaining hoses weak, may increase the likelihood that one of the weaker hoses will fail. Check the condition of belts. Belts can break or become stretched, glazed or frayed. If belts become ineffective in turning the radiator fan, for instance, this may be another cause for overheating. If a fan belt is slipping, you may be able to help the situation by tightening the belt or using a belt dressing. It's generally best, however, simply to replace the belt. Other problems that can contribute to engine overheating include a faulty thermostat or a water pump that's not working. If these parts fail, it's best to stop the car and seek the assistance of a mechanic. Remember that a severely overheated engine can cause engine damage. An indicator that overheating may have occurred is if the engine oil has taken on a black color and thick consistency. If this is the case, discontinue driving the vehicle immediately and contact a mechanic. PDF Illustrations Illustrations may be viewed by using Adobe Reader® Click here for a PDF showing the components of an automotive cooling system.
Click here for a PDF showing a water pump.
RESOURCES :
The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books
Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896
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