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Cooling System Flush
Cooling System Flush

When should I flush my car's cooling system?

       Replacing coolant on a regular basis will prolong the life of the radiator and other cooling system components. Most new car maintenance schedules call for coolant changes every three years or 50,000 miles. Many professional mechanics consider that too long and recommend every two years or 24,000 miles. There are some who argue that annual coolant changes on late model vehicles with bimetal engines (aluminum heads/iron blocks) and/or aluminum radiators are a good idea. It does not really make much difference how often the coolant is changed as long as it is changed before losing its corrosion resistance. When coolant is changed, the system should be reverse flushed rather than simply drained. This helps dislodge and remove accumulated debris and debris in the system. It also removes old coolant that would otherwise remain in the engine block. Use of a cooling system cleaner is not necessary unless the system has been badly neglected and is full of lime deposits. A good technician will flush the engine block and heater core. He will clean out the overflow bottle and test the radiator cap. He will fill the cooling system with a 50/50 mixture of coolant. He will pressure test the system at a few pounds over the normal operating pressure. If after a short time there is no pressure loss indicating a coolant leak and none of the hoses blow or swell up, then all is OK.
Remember that antifreeze needs water to work. Antifreeze is made of ethylene glycol (which never wears out) and various additives (which do wear out). You should never use a mixture of more than 60% coolant or antifreeze. It's the anti foaming agents, the rust inhibitors, and the water pump lubricants that wear out. With the price of plastic tank radiators approaching $400 and damage related to the deterioration of aluminum timing covers costing $600 to $1,000 to repair, why not spend between $50 and $85 for a yearly flush? Some additives provide "reserve alkalinity" to neutralize internal corrosion before it can start. As long as the coolant is changed before its reserve alkalinity is depleted, the cooling system should be no worse for the wear. If you wait too long, the result can be expensive internal corrosion in the radiator, heater core and engine.

How can you tell when it is time to change the coolant?

   The only way to know if the coolant still has adequate corrosion protection is to test it. By dipping a test strip in the coolant and noting its color change, you can determine coolant condition and whether or not it is time to replace it. When coolant is changed, inspect belts and hoses. Make a visual inspection for leaks. Pressure test radiator and cap. Check operation of heater and defroster. The thermostat does not need changing unless it has been causing trouble or the engine has severely overheated. If a thermostat is replaced, it should have the same temperature rating as the original. This is extremely important on late model vehicles with computerized engine controls. Fuel, ignition and emission functions are all affected by coolant temperature.

How does your cooling system works?

   The water pump pumps the coolant and water mix through the engine. The job of the liquid is to pick up the heat and carry it to the radiator so it can be dissipated. The water pump can't pump foam, so they put antifoaming agents in the coolant. We know that every car that overheats does so because of the lack of coolant (because of a leak) or because of a restriction of the flow (closed thermostat, plugged radiator, or a water pump that's not pumping because of a drive belt that broke or an impeller that's come loose).
The thermostat's job is to open when the coolant gets too hot and let the coolant travel faster into the radiator. If it senses the coolant is too cold, it closes to slow down the flow and keep the coolant in the engine longer. We all know that water boils at 212 degrees Fahrenheit. For every pound of pressure you put water under, it will increase the boiling point approximately 2 degrees. So a good 15-pound radiator cap will raise the water's boiling point 30 degrees from 212 to 242 degrees Fahrenheit. Add 50 % of coolant and the boiling point of the mixture is well over 260 degrees Fahrenheit. The water pump circulates the coolant through the motor. The water pump can't pump steam. Which is why the coolant has to stay in a liquid form. It's important to know that today's cars to operate at 205-220 degrees Fahrenheit. So if the coolant turns to steam too early because of a bad radiator cap or a weak mix of coolant and water, the car will overheat at 230 degrees or so, which leaves little room for an extended stop at a traffic light on a hot summer day. Very few overheated cars are fixed with just a radiator cap and I've never seen a car fixed with a flush. Flushing a car to fix an overheating problem is like rinsing out your mouth with mouthwash to kill cavities. A flush is done as maintenance or after the repair, not as a repair.

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Last modified: 03/11/2003