radiator anatomy

Know-How Notes: Inside Your Radiator

The largest component to your vehicle’s cooling system is the radiator, but did you know that the radiator is also connected to your transmission and in some cases your engine’s oiling system too? Inside your radiator are smaller radiators that help keep your transmission fluid and engine oil cool as well.

The basic radiator consists of two tanks with a set of tubes connected with thin fins that radiate heat away from the tubes. As air passes through the fins, the heat is carried away, lowering the temperature of the fluid running through the tubes. Modern vehicles use aluminum radiators, most with plastic side tanks, but there are also copper and brass radiators. Aluminum is used because it is light and the tubes can be made thinner, allowing the radiator to have more cores (sets of tubes) than a comparable copper radiator. This is what makes an aluminum radiator more efficient, copper actually conducts heat better than aluminum, but the extra core increases cooling capacity. Aluminum is also cheaper to manufacture.

Tanks For The Memories

Astride the cooling core, are two tanks. Some are plastic, some are aluminum or brass. Aluminum or brass tanks are welded to the core, while plastic tanks are attached with tabs and a seal.  The tanks hold the coolant, one is the intake side, one is the outlet. Most modern radiators are of the crossflow variety, meaning the coolant flows from one side to the other. Some units use a 2-stage cross flow, where the tanks are split in half, forcing the coolant to flow through the radiator twice, increasing the cooling capacity of the radiator. Many older vehicles, pre-1970s, use vertical flow radiators, where the coolant enters the top of the radiator and flows down to the bottom tank. This is less efficient and has not been used much since the late 1960s.

Copper and brass radiators have metal tanks that are soldered together. Some aluminum radiators have welded tanks as well.

Copper and brass radiators have metal tanks that are soldered together. Some aluminum radiators have welded tanks as well.

 

Most modern radiators have plastic tanks retained with metal tabs. You can remove the tanks for servicing, but this is NOT a DIY project.

Most modern radiators have plastic tanks retained with metal tabs. You can remove the tanks for servicing, but this is NOT a DIY project.

Core Components

The core itself consists of flattened tubes connected with a web of thin fins. The air is pushed or pulled through the fins, pulling heat away from the tubes. Each set of tubes and fins is called a row or core. Most aluminum radiators have four cores, while copper/brass radiators typically have two cores. Copper/brass cores are nearly twice as thick at aluminum, and even though copper and brass are better heat conductors, the ability to add more cores with aluminum makes aluminum cores more efficient when stacked up.

The core is the assembly of cooling tubes and fins. This single-row aluminum core has a fair amount of grit build up, this radiator needed to be flushed more often. The oval openings are where the coolant enters the tubes.

The core is the assembly of cooling tubes and fins. This single-row aluminum core has a fair amount of grit build up, this radiator needed to be flushed more often. The oval openings are where the coolant enters the tubes.

Cooler Than Nothing

Nearly every modern vehicle these days has an automatic transmission. In order to function, the transmission fluid needs to be cooled. If the transmission is run without a cooler, it will quickly reach 300 degrees, which will destroy the fluid and subsequently the transmission. You could use a stand-alone transmission cooler, but your vehicle’s transmission actually operates better at around 160-200 degrees than it does when cold. By placing the fluid cooler inside the radiator, the engine’s coolant helps bring the transmission up to temp faster and maintains a consistent temperature better than a stand-alone. If you are towing, however, an extra cooler, used in addition to the radiator trans cooler, will help keep the transmission from overheating. The cooling tubes for the transmission cooler are usually located inside one of the tanks.

On the side of the tank, most vehicles have fluid ports for transmission fluid. They look like this and use wire retainer clips to hold the line in place.

On the side of the tank, most vehicles have fluid ports for transmission fluid. They look like this and use wire retainer clips to hold the line in place.

 

The replacement radiator we installed on this vehicle came with the plastic line removal tools, they make it easy to get the lines out and they are reusable.

The replacement radiator we installed on this vehicle came with the plastic line removal tools, they make it easy to get the lines out and they are reusable.

 

This is the wire retaining clip, don't lose it. If you use the plastic tool, the clip stays in the fitting, so no worries about misplacing them.

This is the wire retaining clip, don’t lose it. If you use the plastic tool, the clip stays in the fitting, so no worries about misplacing them.

Oily Solution

Much like the transmission cooler, some vehicles have an oil cooler mounted in the tanks. This is most commonly used for trucks and high-performance vehicles, but not exclusively. Keeping the engine oil cool increases the engine’s performance, longevity, and allows for longer oil change intervals. When oil heats up, it starts to break down. Where transmission fluid can reach 300 before breaking down, engine oil starts this process at just 240 degrees, which is very close to operating temps of 200-220 for modern engines. Reducing that oil temp is critical, especially for high stress engines like trucks and high-performance vehicles. These cooling tubes are also usually found in one of the coolant tanks.

Inside the tank, the auxiliary coolers for oil and transmission fluid look like this. There is not much room to spare inside the radiator. Where the fittings connect are a common area for cracks.

Inside the tank, the auxiliary coolers for oil and transmission fluid look like this. There is not much room to spare inside the radiator. Where the fittings connect are a common area for cracks.

In Reserve

Nearly every modern vehicle uses a reserve tank to serve as the overflow tank and filling point of the radiator. Before these tanks, there was an overflow tank that would hold excess water in the event of a purge from the radiator cap, but the coolant was not returned to the radiator, so you were left with low coolant. Over time, this was developed into a strategy where the reservoir tank takes in excess coolant when the water expands as it heats, and returns it back into the cooling system as the coolants cools. This prevents the old problem of losing coolant.  

The reservoir tank holds the coolant as the coolant expands and contracts throughout the cooling cycle.

The reservoir tank holds the coolant as the coolant expands and contracts throughout the cooling cycle.

Whether you are needing to replace a stock radiator or upgrade to increase your cooling capacity, the right sized radiator is available for your car. Just be sure that the inlet and outlet are in the right place and the right size. Direct-replacement radiators for just about every car are available at your local NAPA AUTO PARTS Store.

To learn more about NAPA AutoCare, visit www.NAPAAutoCare.com.

about author

Jefferson Bryant

A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.

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