The radiator is part of the cooling system, which is supposed to be a contained system. As the radiator ages it can may fatigue and begin to leak through cracks that develop, or, it may rot from the inside out and develop pinholes.
If it’s a significant leak, it needs to be dealt with directly. Sometimes at the early stages when the leak is only at a level of minor seepage, people will monitor the coolant level and live with it till it’s progressed to a more significant rate of loss.
However, loss of coolant can cause catastrophic engine failure due to overheating.
If you have any known leaks in the radiator, then at minimum, you should regularly check your car’s coolant level and keep a careful eye on the temperature gauge. Due to the possible serious consequences of any lapse in your vigilance, it’s probably best to simply perform the needed repairs.
Radiators can also fail due to clogged, restricted passages. When this happens, the coolant isn’t able to flow through the radiator at a sufficient rate to cool the engine. This results in the greatly increased likelihood that your engine will overheat on hot days or when going up hills. If you know that your radiator is plugged up, you should treat this a s high priority repair.
When checking your coolant level, check both the plastic overflow reservoir and the radiator itself. As the coolant heats and expands, some of it goes into the overflow reservoir. As it cools and contracts, it is supposed to be sucked back into the radiator. It’s no good just checking the overflow, because if the cooling system isn’t sucking the coolant back into the radiator properly, it’s possible to have a full overflow and an empty radiator. You want both levels to check out right, but of the two, the coolant in the radiator is the coolant that’s actively involved in cooling the engine; this is the coolant level that’s most critical to be full. Check coolant levels when engine is cool to avoid risk of being burned by hot coolant coming out of the radiator under pressure.
Note: We have a real aversion to the use of chemicals put into the cooling system for the sake of stopping leaks from the inside out. These chemicals purport to plug up the leak, which sometimes they do for awhile, but they also tend to plug up cooling passages with the result that the engine can overheat and develop worse problems that are far more expensive, like a blown head gasket. Stop-leak additives can also cause the heater core passages to get plugged up, which results in your heater not heating properly.
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