Modern radiators can cool an engine extremely well. While the majority of heat produced by internal combustion is vented into the atmosphere through the exhaust system, the remainder is absorbed by engine coolant circulating through the engine’s water jackets and cylinder heads. The hot coolant is then pumped into the radiator, where heat is transferred through the radiator core tubes into the cool atmosphere. The radiator also does double-duty dispersing frictional heat produced by moving automatic transmission parts through the transmission oil cooler built into the radiator header tank.

As you might suspect, rust and scale build-up inside the radiator tubes seriously reduce the radiator’s ability to dissipate heat into the atmosphere. Clogging caused by dirty coolant or by gasket material and sealants flaking away from the engine also reduces the cooling capacity of the radiator. In addition, the radiator’s delicate aluminum cooling fins are often damaged by airborne road debris, which additionally reduces the radiator’s cooling capacity.

 

Radiator Construction
Most early vertical-flow radiators were made of an upper “header” tank soldered to a brass header plate holding the radiator core tubes in place. The lower plate and outlet tank was of similar construction. Unfortunately, vertical-flow brass radiators were heavy, expensive and environmentally challenging due to the liberal use of lead-based solder.

The cooling capacity of most radiators can be increased by adding extra rows of core tubes. While single-row radiators can cool a small-displacement engine, up to four rows of core tubes are required for heavy-duty applications. In terms of increasing cooling capacity, adding more than four rows of core tubes generally produces diminished returns. Consequently, the frontal area of the radiator becomes more important in determining cooling capacity. Additional cooling capacity can be achieved by manipulating the shape and density of the aluminum cooling fins inserted between the core tubes. But, when the cooling fin density becomes too great, air flow through the radiator is reduced at normal road speeds.

During the 1960s, most auto manufacturers adopted the horizontal-flow radiator design that is used to this day. Most horizontal-core radiators crimp an aluminum core tube assembly onto plastic header tanks, which are sealed to the core with rubber gaskets. In conventional cooling systems, the inlet connection is located at the radiator top while the outlet is located at the diagonally opposite corner but some high-performance sports cars flow from bottom to top. The inlet connection will generally be smaller than the outlet connection.

 

When To Replace
Given enough time and mileage, rust, scale and debris will eventually clog a radiator’s core tubes. A lifetime of road vibration, thermal stress and pressure cycling may also cause the core tubes to crack due to metal fatigue. Engine boil-overs can also lift sludge from the bottom of the engine’s water jackets, which will rapidly clog an older radiator already full of rust and scale.

Consequently, any vehicle with more than 100,000 miles on the radiator is a perfect candidate for a radiator inspection and evaluation. If the coolant is excessively rusty or the radiator core is excessively damaged from road debris, it’s time to consider replacing with a new, OE-fit radiator.

To prevent clogging the new radiator, it’s always best to flush as much of the old coolant as possible from the engine before installing the new radiator. When installing new coolant, it’s usually more convenient to install 50/50 premixed antifreeze and water. This will ensure a lifetime of good performance from the newly installed radiator.