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Head gasket failures are relatively common in all forms of racing, and most racers know how to repair the damage themselves, or have an engine builder who can do it for them in short order. However, theres’s an often-overlooked and very serious by-product of a blown head gasket that every gearhead needs to be aware of: cooling system pressurization and the potential damage to your radiator. Eric Saffell of AFCO Racing Products recently took the time to share some vital information about this subject, from diagnosing potential problems to a course of action that could potentially save your hot rod – and you personally – from a devastating crash caused by a failure within the radiator.

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Head gaskets can fail for any number of reasons, and in a number of different places across the surface between the head and block. Not all head gasket failures lead to cooling system pressurization, and fortunately there is a very simple visual check to see if your radiator has been compromised.

Within the radiator, running horizontally between the tanks on each end, are capillary tubes. These tubes are flat and have tiny accordion-like fins between them. These capillary tubes carry water through the fins, which direct airflow over the tubes. This is where the actual exchange of heat takes place, so any damage to this structure will likely cause the cooling system to lose its ability to maintain steady temperatures, and cause it to cool more slowly when you return to the pits. These changes can be subtle and may not seem like a major issue, but should prompt a check of the cooling system itself, especially following any engine damage.

This image is the best visual reference for showing exactly what happens when the cooling system encounters pressurization from a head gasket failure. On the right, an undamaged radiator with the thin, flat capillaries as they should be. On the left, the capillary tubes have been blown up and take on a football-like shape, which crushes the fins between the tubes. With these fins collapsed, no air can flow over the capillaries, and no heat can be exchanged. If the radiator can't dissipate heat, it cannot keep the water cool, and problems will arise almost immediately.

This image is the best visual reference for showing exactly what happens when the cooling system encounters pressurization from a head gasket failure. On the right, an undamaged radiator with the thin, flat capillaries as they should be. On the left, the capillary tubes have been blown up and take on a football-like shape, which crushes the fins between the tubes. With these fins collapsed, no air can flow over the capillaries, and no heat can be exchanged. If the radiator can’t dissipate heat, it cannot keep the water cool, and problems will arise almost immediately.

To check for damage, the process is simple and quick: look! Simply remove the radiator from the car and hold it up to the light in your shop or garage. A healthy radiator will have plenty of room for the light to shine through. A damaged radiator, however, will allow very little or no light to pass, and that indicates it’s time to replace the radiator. “You can see in the photo, the capillaries are nice and flat and uniform, then after pressurization occurs, they get blown out into a sort of football shape,” Saffell explains.

Tracking Down The Cause

Over the years, AFCO has been able to track down the cause of this ballooning phenomenon, thanks largely in part to some hard-charging circle track racers, recounts Saffell. “We would have round-track racers who were running the last few laps of a big money race, when they would notice the temperature starting to climb.” As most of you can imagine, the chance of these guys heading to the pits because the temperature is climbing is close to zero, so this led to plenty of overheated engines and blown head gaskets. “Those guys would send their radiators back so we could check them out, and that’s when we learned exactly what was causing this.”

An AFCO staffer welding a radiator during the assembly process. AFCO offers a wide variety of sizes and layouts, and they can also build a radiator to your custom specs. Unlike many radiator manufacturers, AFCO doesn't jack up the prices for custom built designs, helping eliminate the need for customers to modify their product and potentially shorten its lifespan.

An AFCO fabricator welds a radiator during the assembly process. AFCO offers a wide variety of sizes and layouts, and they can also build a radiator to your custom specs. Unlike many radiator manufacturers, AFCO doesn’t jack up the prices for custom-built designs, helping eliminate the need for customers to modify their product and potentially shorten its lifespan.

Saffell also recounted a boosted drag car that received an upgraded pair of turbochargers, then experienced the same ballooning following a subsequent head gasket failure. This time, however, the pressures were much higher than those seen in the naturally aspirated round track cars, which provided some insight into just how extreme the pressures can be when air is crammed into the cylinder. AFCO techs have also seen similar results from nitrous-assisted combinations that have torched the head gasket due to the increased cylinder pressures in those applications.

Replace, Don’t Repair

An example of bent fins on a radiator. While some bent fins are to be expected from normal wear and tear and handling, any area more than 3-4 in diameter presents a significant cause for replacement of the radiator.

An example of bent fins on a radiator. While some bent fins are to be expected from normal wear and tear and handling, any area more than 3-4 inches in diameter presents a significant cause for replacement of the radiator.

To put it quite simply, you cannot adequately fix a radiator. The capillary tubes are made from thin aluminum by design, to promote faster, more efficient heat transfer. The fins between the tubes are also very thin and are constructed very specifically to direct airflow over the tubes, another important factor in proper cooling. When pressurization of the cooling system occurs and the capillaries balloon from their original shape, the fins between them are crushed, cutting off most, if not all, airflow across the tubes. If air can’t flow across the tubes, there’s no heat dissipation, and the water will simply hold heat as it passes through the cooling system, leading to cooling issues and a host of potential problems elsewhere in the engine.

If the forces involved in the pressurization are strong enough, the damage can go beyond simply ballooning the capillaries and lead to actual structural failure of the radiator in the form of cracking. These cracks can lead to fluid loss at the time of the pressurization and a possible crash if that water gets under the tires. However, cracks don’t always reach the point of leaking right away and instead will worsen over time due to vibration and stress. Eventually, the compromised areas will weaken to the point of leaking, often while the car is screaming at wide open throttle, since this is when the cooling system is under maximum stress.

Here are just a few samples of some of the endless applications AFCO builds radiators for. From street rods to custom engine swap applications to full-bore drag racing applications, they can build the radiator you need for your hotrod.

Other Causes Of Failure

Ballooning the capillaries from pressurization isn’t the only cause of radiator failure. Saffell says another cause of of damage they’ve seen at AFCO is from severe tire shake often experienced in today’s ultra-high horsepower cars.

“We have definitely seen damage caused by tire shake,” he said. “In those cases, the damage can be anywhere in the radiator,” as the stresses caused by tire shake can show up in a number of ways. Any time a car experiences severe shake, a careful visual inspection of the entire radiator is a must.

“Often, tire shake will lead to visible cracking that many racers will try to repair with epoxy or stop-leak, but that is, at best, a band-aid,” Saffell says. Epoxy can and will stop the leak, but it takes only a small percentage of the amount of stress that caused the original damage to compromise the epoxy, which could come from something as common as the transmission shifting or a bracket racer “whomping” the throttle at the finish line.

One of AFCO's fabricators putting the finishing touches on a custom radiator. Offering custom builds eliminates the need for customers to modify radiators for their specific, and often unique, build.

One of AFCO’s welders putting the finishing touches on a custom radiator. Full custom builds include custom widths and mounting options and take cooling needs into consideration to ensure perfect fit and that the system performs as expected.

“We have seen cases where a racer used a radiator from one car in another application that required some modification [to the radiator],” Saffell explains. “They will take it to a buddy to modify it, and that’s generally a bad idea.” Any modification to an aluminum radiator, especially welding, stresses the material and can cause it to become brittle, which causes a weak point in the radiator. “We build fully custom radiators all the time, and unlike some other manufacturers, we don’t jack up the prices two or three times for one-off radiators,” Saffell adds.

Custom + Affordable = AFCO Radiators

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AFCO prides itself on its ability to provide customers a fully custom radiator for any application for a price comparable to their off-the-shelf units instead of doubling or tripling the price, as some competitors do. If you have a unique application or just want to make sure your radiator fits perfectly, don’t hesitate to inquire about a custom unit built to your specifications.

Perhaps the most common cause of radiator failure is time itself, and this is also the hardest to predict, as it can come after years of flawless performance with little to no warning.

“At the beginning and end of each season, just give the radiator a good visual inspection, looking for signs of cracking or flexing, and tell-tale signs of water leaking, which will leave a white chalky residue on the outside of the radiator,” Saffell advises. AFCO also recommends doing the shop-light check anytime the heads are taken off the car due to a head gasket failure, just to check for signs of swelling in the capillary tubes.

The information we’ve presented here will hopefully help you identify any potential problems with your radiator before they become major issues. While radiators are generally pretty durable and can last many seasons, they do need to be inspected regularly and maintained properly to ensure they reach their maximum longevity and maintain their efficiency. Following this plan will help your cooling system keep your hot rod running cool for a long time.