What happens if you don’t maintain the coolant? You can have serious damage to the engine itself. But even considering just the radiator, you can have all kinds of trouble, partly because untreated coolant gets like an acid. Acid works with the corrosion caused by bad coolant to create damage and leaks.
Many radiators today use plastic top and bottom tanks sealed with thick gaskets. The tank is crimped around the gasket and the header plate at the top or bottom of the core to hold the gasket in place and make a seal.
When the coolant goes bad, it often erodes the gasket, Mascuch and Sholly say. Soon, much of the thickness is gone, the gasket no longer seals, and you get a big leak. Another problem is with the tank itself. The acid can erode the tank on the inside as the coolant flows through it, washing the plastic away, it until it becomes quite thin.
“Corrosion blocks the tubes and slows the flow,” Mascuch says. “Pressure then builds up in the system; even the normal operating pressure under favorable road conditions will be higher. This puts excess pressure on the tank tabs, and they break. Or the combination of pressure and temperature and erosion of the plastic causes the tank to crack.”
These effects may also cause the tank to warp and not fit.
The clogged tubes may also corrode through and leak, necessitating a repair or core replacement. The acid actually corrodes the lead in the original solder, just as it corrodes those lead battery terminals, and that can make the tubes leak at the ends even if they don’t rust through.
The cooling fan and thermostat
During highway operation on level roads, the airflow needed to keep the radiator working is provided by ram air. But when running in traffic or climbing steep grades at lower speeds, the cooling fan clutch engages to provide airflow. This system is subject to mechanical problems with the clutch, or on early models with a separate sensor and wiring for the fan, wiring and sensor failures. These can result in higher-than-normal operating temperatures under certain conditions. That means extra radiator stress.
You’ll hear the fan come on and often feel it because of the drag. Keep your eye on the temperature gauge and remember the point when the fan engages, usually 15 degrees F. or so beyond the point where the thermostat opens. If the fan starts coming on at too high a temperature or fails to come on at all, have the problem repaired right away.
The thermostat is another critical part, and it can become lazy and open late. This, too, will increase the pressure in the system and put unnecessary stress on the radiator.
Although it is normal for the operating temperature to rise somewhat in warmer weather or when running under heavier loads, it should still remain within a narrow range. If it creeps upward, have the thermostat checked.
The thermostat should ideally be replaced every year or two, anyway, Sholly says. Maximum life is five to seven years. She says the thermostatic spring goes bad eventually and, “Don’t wait until it sticks and gives you more problems.”
Sholly also recommends using only an OEM unit, as some aftermarket units may be unreliable and not keep the engine at the proper temperature. Her shop has solved more than a few troubles by replacing aftermarket thermostats with original equipment. And always use new gaskets and seals with the ‘stat.
Getting the repair
Once you develop a radiator leak, there’s only one thing to do – get it repaired.