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février 03, 2021 7 min read

Often overlooked, the radiator is a key part of your cooling system and it is of the utmost importance to ensure your radiator is not only fit for its purpose, but also in good condition. It should be maintained along with all the usual servicing requirements and periodically checked for damage or blockage. Radiator cores are generally very delicate, and it is not uncommon to see damage due to corrosion or impact from external sources.

Years ago, the radiator was an important focal point of the aesthetics of the car. Cars of the period which we now regard as classics had huge chromed front grilles, these assemblies were typically made in copper and brass, meticulously handmade, soldered and finished. This was one of the main aesthetic features of the vehicle, and as such they were cherished as the “emblem” of the marque.

Moving onto the modern day, a radiator is barely visible as it is wrapped into a tight-fitting cooling package, obscured from view by plastic trim, air con systems and other ancillary parts. They are usually buried under front panels and in most cases they are not particularly easy to access. This can encourage an almost, “Out of sight, out of mind” approach, and unfortunately, we do find that the radiator is a rather unloved component.

Buying an intercooler tends to create an amount of excitement, as there is a performance benefit to be gained from the investment. An improved radiator does give increased performance, but it’s not a difference that can be felt in the same way. Nevertheless, your engine needs a reliable water cooler, adding power to an engine’s output is all well and good but the thermal loads placed on the system will need to be addressed. In the next few paragraphs, we will list some of the issues that we often come across.


Aluminium Radiators and Heat Dissipation.

As we have already learned, aluminium is a great material for dissipating heat. It is lightweight, being approx 50% lower in mass than a copper / brass unit and it is a very workable material which is great for fabricating into complex shapes. What you’re looking for with an effective radiator is capacity to bring the coolant temperature down sufficiently in the cycle from hot engine outlet to cool water inlet. With a tuned engine the water on the hot side will have absorbed more heat than usual, so there are further demands on the core to provide an increased level of heat transfer. Consistently overheating an engine will destroy head gaskets, plus a further risk of cylinder head warpage or cracking. High water temperatures will also keep residual heat in the water jacket, driving up combustion heat and placing additional demands on key components.

In short, the radiator is very much a key part of your vehicle’s cooling system, and its role in maintaining overall reliability must not be underestimated.


How to Improve Cooling System Performance.

The performance of the radiator can be improved by adding capacity, either by creating a core with a larger surface area, or by adding depth (thickness). Given the choice, it is better to add surface area as this will result in a more dramatic result in terms of heat loss. In practice however, making a radiator either taller of wider is quite difficult to achieve given the packaging constraints of the vehicle. Unless you want to start trimming material from the front panel, there is not usually much scope for growing the dimensions in this way.

Adding capacity by making the radiator thicker is still a worthwhile exercise, but it doesn’t give quite the same gains due to the inefficiencies of restricting airflow. We can combat this by building the core with a more open fin structure, but it’s important not to do this at the expense of thermal transfer.

One often misleading theory is that multi row cores are better in terms of performance than single row units. In practice, there is more to this than simply adding up the number of cooling tubes and assuming that quantity wins the day. The calculation required here is tube volume, and it is very easy to see how a single row, wide port tube is larger in its port area than two smaller tubes sat side by side. Further to this, a single row core doesn't have any divisions in the flow path, and they also have a better surface contact to the cooling fins. Cutting the two core types down the middle and examining them in cross section reveals the difference in design, and further measuring often yields evidence that more core tubes is not always the better choice.

Most OE fan assemblies are fitted with relatively deep motors, which take up a lot of space. We often create more space by using slimline fans, this then gives us the opportunity to grow the core depth back towards the engine, thereby increasing capacity to the benefit of system performance. A common misconception is that fitting a large header tank will create better cooling, but this is not the case. In that scenario the larger volume of water will take a little longer to reach normal running temperature, but after that you simply have more hot water, not better cooling.


Antifreeze Mixes and Cooling System Problems.

Coolant / antifreeze mixes have changed a lot over the years, and these days it can be confusing when it comes to choosing a brand to suit your application. Years ago, the best you could do would be to mix distilled water with antifreeze in the correct ratio, and for most applications this is still ok, if the mix is changed at sensible intervals. These days, manufacturers tend to use their own specific coolant and these are often used undiluted. However, it is still important to change your coolant as specified in the vehicle’s service schedule.

As most of the vehicles we work with are project or classic cars, it is not uncommon to see vehicles taken off the road for the winter, and sometimes it can be quite difficult to recall when the coolant was last changed. Our advice is to change it every two years, regardless of the amount of mileage covered. This is because the quality of the coolant will degrade even when it is sitting still, and in some cases this can lead to some very unwelcome situations.

The following section will point out some of the problem areas that do often arise, and it is important to ensure that your vehicle is not suffering from any of these issues.


Residual Voltage In Cooling Systems.

This can be measured via a simple voltmeter, with one terminal fitted to the earth of your battery and the positive probe inserted into the coolant. With a warm engine running at roughly 2000 rpm, check the display for voltage. Anything more than 0.5V here is certain to cause problems and it is essential to change the coolant and check your earth terminals.

This is something that generally affects classic cars, but it’s not impossible to see it affecting newer vehicles. You have several different metals in your cooling system, and these metals react differently in terms of their electrical properties. Voltage will occur when dissimilar metals react with each other, this process is known as electrolysis, and although there are certain additives in a coolant mix to help prevent it, these additives break down over time with the result that the voltage levels can increase.

The electrical system in your car will have some means of earthing the engine to the chassis, traditionally this was done via a braided steel cable. If there were to be significant failure of the earth point, either due to cable damage or corrosion, it will exacerbate the problem with potentially harmful results. 

Examples above showing the effects of galvanic corrosion, an unwelcome effect that occurs between dissimilar metals.


Galvanic Corrosion.

This is a thoroughly undesirable mechanism, and in these cases it occurs when you have an electrolyte circulating between dissimilar metals. In the marine industry, boats and watercraft often use zinc tabs in the water, these are sacrificial anodes and need to be replaced as they are eaten away by the effects of galvanic corrosion, thereby helping to protect the parent materials.

In the automotive application, the reactive materials, such as the aluminium in your radiator or water pump will become the sacrificial anode, and the process can create tell-tale signs on alloy components such as a build up of white powder and severe pitting of the metal surfaces. In extreme cases, the alloy will become so degraded that hose connections crumble away, or even worse, a cylinder head with barely any gasket surface left intact. Aluminium will not stand a chance in this scenario, so do pay careful attention to regular coolant changes, especially if the car is stored for long periods.


Internal Blockages and Cooling System Performance.

This image shows the core internals packed with metallic flakes, blocking the radiator and preventing efficient flow. This can occur when a car with an iron engine block has a corroded water jacket, and the loose fragments of iron oxide get trapped in the core orifices. The obvious effect this has is to dramatically reduce coolant flow and will cause overheating and a rise in system pressure. In these circumstances a cooling system flush will not be sufficient and a re-core will be the only cure.

The longer term fix is a complete engine strip down and chemical block treatment to break up the iron oxide. With regular coolant changes / system flushes, this is an avoidable situation, but old engines that have been stored for years should have a thorough inspection prior to being built up.

Again, the introduction of dissimilar metals will potentially accelerate the corrosion process here, and unfortunately it all happens from within so will be invisible until the problem becomes obvious. By this point the damage has long been done and the radiator will need to come apart, or in the worst cases, completely replaced.

In this section we can see that alongside the arduous task of engine cooling, the radiator and its associated components live a very hard life. Certainly, we can say that the radiator circuit has many more challenges in its life than an intercooler, so do give careful consideration to this often-neglected area!