It all starts with heat. The modern automobile uses fossil fuel to produce heat to create expansion, that is harnessed in an engine, that produces torque, that moves our vehicles. The more heat that can be produced, the more torque or power that can be created. Depending on the efficiency of the engine, and many other variables, waste heat is produced and must be "shed" or overheating can occur. To accommodate the cooling needs of the engine, a method of moving excess heat from the engine must in place. Today's engines use liquid cooling to accomplish this. The advantages of liquid cooling are:
Even heat distribution
Easy heat transfer
Efficient movement of heat
Effective control of heat
The heat from the engine is absorbed by the engine coolant (remember in science class, heat always moves from hot to cold). The automotive radiator is designed to move heat from the hot engine coolant and transfer this heat to the surrounding air as the coolant moves through the radiator. Typically, the hot engine coolant enters the radiator at the top, and exits the radiator at the bottom. As the coolant moves through the radiator, it "heats up" the radiator tubes so that the radiator can begin the heat transfer process. As the tubes get hot, the heat then moves to the fins, then to the air. The result is that as the coolant leaves the radiator, it has lost some of the heat that it carried in. Success.
Overheating almost always occurs due to insufficient coolant flow through the radiator. If the radiator has restricted coolant passages (called tubes) insufficient heat transfer will occur. This is quite common when proper cooling system maintenance has not been followed, or if the maintenance schedule is inappropriate for the vehicle. The tubes in the radiator allow heat to escape, If the tubes are restricted, only a percentage of the cooling will occur, and vehicle overheat is likely. Many times a radiator can be restricted 30%-40%, and the only symptom is overheat on hot days, or climbing hills or towing. However, as the restriction gets worse, the overheat gets worse, and the symptom is often expressed as "on the freeway, the faster I go, the hotter it gets". The process of cleaning a radiator known as a rod out will restore the coolant flow to near 100% of capacity.
Another common overheat problem occurs when the thermostat sticks closed, or partially closed. The thermostat blocks flow to the radiator when the vehicle is cold, so that the engine has a chance to warm up quickly and reach the correct operating temperature. This is vital for exhaust emission reasons as well as fuel economy concerns. Operating temperature is an extremely important part of the engine computer strategy, and just as too hot is not desired, too cool is not good either. The thermostat must delay hot coolant flow to the radiator until just before the correct temperature is reached. As the thermostat opens, heat begins to move from the coolant to the outside air, just a little at first, then a lot. The thermostat can open just a bit (cold winter nights) or be open fully (summer days). It must be capable of adjusting it's position to the heat load.
If the air passages (called fins) are severely damaged or corroded, insufficient heat transfer will cause overheat. Remember, the tubes must heat the fins, that heat the air. If the fins are missing, loose, corroded, or severely damaged, we won't be transferring enough heat. If fins have become a problem then recoring can restore heat transfer.
Contaminated cooling systems have additional concerns that must be dealt with
If the radiator is undersized for the application (new motor, lots of HP) over heating can occur. Proper sizing of a radiator and sufficient flow rates both contribute to adequate cooling.
Antifreeze or Coolant are both basically synonymous terms used to describe the fluid that is used to transfer the heat from inside an engine, to the outside, where the radiator and heater can remove it. Lots more on coolant here.
The radiator is only as good as the flow of hot coolant being delivered to it. More on coolant here. If the thermostat is stuck in the closed position, rapid overheat will occur, usually within 1 or 2 miles. The water pump must also be functioning correctly for proper cooling . Plastic components are finding their way into water pumps (and everywhere else) and have been found to be the source of trouble. If a radiator is determined to be the cause of overheating or leaking, three options exist:
Many times radiators are damaged by road debris that comes through the grill, or sometimes by "under hood events" (someone working on the car). Often improper mounting plays a part in a radiator failure, and this can usually be spotted by a trained eye. If the radiator is strong enough, a good repair is often all that is needed. The repair differs, depending on the cause of the problem. The repair is still considered one of the best values out there. When a radiator is leaking because it is corroded or rusty, it is often not considered repairable, and other options like recoring or replacement are then discussed.
Rod out- To take apart a radiator by removing at least one tank, inserting a metal rod through each water passage (tube) to ensure near 100% water flow. Reassemble radiator, pressure test, flow test, rinse and dry. See more.
Recore-To remove both tanks and both brackets from the old core, and install them on new core with new hardware and a new drain cock, pressure tested, flow tested, dried, and painted. See More.
Replacement
- Replace-Sometimes it is better to start over. Brand new radiator are available for a wide variety of cars. Some have 3 year warranty's* and others come with lifetime warranty's*. *See warranty for details.
Very common these days are remote filling points. They allow a convenient place to add water and coolant, and allow smaller radiator to be mounted in untraditional ways and places, under panels, or structural bracing, to allow better air flow (wind tunnel ) characteristics. See more.