Cooling is a constant concern for the street machiner, and with the hot weather any problems that have lain dormant during the colder months will surface and put a crimp in your summer cruising style. So, among other things, a quality radiator is a fundamental step in improving your system and Norm at Aussie Desert Cooler told us what to look for.

First published in the December 2002 issue of Street Machine

Norm is well known in hot car circles as the man who can supply a system that’ll cool just about anything. Rod Hadfield, on the other hand, has a reputation for building cars to challenge Norm. His ultimate attempt would have to be the 3000hp two-stage supercharged, 27-litre V12 Rolls Royce Merlin crammed into the ’55 Chev (shown below).

This thing is so big that it comes back through the firewall and makes a place for itself between the driver and passenger. So, as you’d expect, cooling this set-up has taken high-quality radiators at both the front and back of the car.

Defining a quality radiator comes down to a matter of effectiveness. One of the most common terms heard is the number of cores or layers of tubes the radiator has from front to rear. The arrangement of tubes shown in photograph 1 above forms a four-core unit. Increasing the number of tubes improves cooling because the greater volume of the extra tubes increases the volume of coolant contained in and pumped through a system. Also, the additional tubes provide extra surface area for dissipating heat to the air passing through the radiator.

Closeness counts

In addition to increasing the number of layers of tubes through the thickness of a radiator core, the number of tubes can also be increased by placing them closer together across the width of a unit and photograph 2 above shows two arrangements. Although half-inch tubes are the type most commonly used there are also wider versions available. However, their increased width means that they must be thicker to maintain adequate strength and thicker walls mean less efficient heat transfer. So half an inch ends up being the most effective compromise.

Of course, tubes alone don’t provide enough cooling so they are joined by fins. Norm says that copper fins dissipate heat with greatest efficiency but that brass fins are stronger. Photograph 3 above shows a close-up of some copper finning and this would be the best material for a high-performance engine. The slots punched into the surface of the fins before they are crimped are there to create turbulence as air flows through the core to increase cooling efficiency. Photograph 4 below shows a sectioned view through a brass/copper radiator core.

As with tubes, the greater the number of cooling fins, the better the unit will perform. However, it’s not quite as simple as that. There comes a point at which too many tubes and fins start to restrict airflow through the core and efficiency is reduced rather than increased. After years of building radiators Norm says he’s found that about 14 fins per inch is the limit before airflow starts to become affected. Inter-tube spacing is between 9mm and 12mm.

Weight problem

The problem with a brass/copper radiator is that it’s heavy. Although aluminium is not as efficient as copper at conducting heat, it’s certainly good enough for a radiator and obviously, much lighter. Photograph 6 below shows a sectioned two-core aluminium unit with its large tube. Aluminium tubes are stronger than brass types so they can be much wider without the need to increase wall thickness.

There are more stresses in radiators than people generally think. Photograph 7 below makes the point. This is actually the original radiator from Gary Myers’ burnout-winning Mustang. If you check out the 2000 Summernats video you can watch it explode. The problem was that after doing all the hard work, the engine stopped. When airflow and coolant flow both ceased, the unit became a giant heat sink, pressure shot up and boom! The car currently has one of Norm’s units fitted along with a supplementary electric pump and electric fans that continue to operate after the engine is shut down.

At their ends, radiator tubes are located in brass (or aluminium) header plates. This area sees considerable stress so the plates need to be thick enough to handle the forces involved. Also, the way the holes are formed is important. Just punching them through leaves sharp and highly-stressed edges. These become weak spots and promote cracking. Aussie Desert Cooler versions are punched in two stages. First, they’re pierced but then the press slows down and applies a drawing action to the edges of the holes. This strengthens the grain structure of the metal at these points and promotes greater mechanical strength.

Photograph 8 above (left) shows a close-up of the holes and the service life of a radiator with such header plates is about double that of one with simple punched plates. The corners of the header plates are also points of concentration for stress so the basic fold-formed corners are run through a press that puts a radius on them as shown (right).

For maximum strength, each end-tank of a radiator should sit in a deep recess around the edge of the end plate as shown in photograph 4. This is because solder doesn’t have much mechanical strength so the recess allows the solder to puddle on either side of the edge of the end-tank. Metal end-tanks are best and Aussie Desert Cooler makes custom units for any application you can imagine.

Notice that each of the end-tanks in photograph 9 above has a plate brazed into it. These restrict access to all of the tubes and force coolant to flow back and forth through the radiator three times. Norm says this results in a system that’s around 15 per cent more efficient than a unit with standard flow.

Not so fantastic plastic

Plastic is great stuff for mass production, which is why OE manufacturers have replaced metal end tanks with injection mouldings that are crimped in place with a gasket for sealing. Although they work quite well, any plastic subjected to endless heat and hot/cold cycles becomes brittle and after some years many of them split. Photograph 10 above shows the connection point for the top hose on an EA/EB radiator. This is just one common example of what happens with plastic.

Unless your cooling system receives regular maintenance you’ll be likely to experience problems. One difficulty is a build up of sludge. The answer is to flush the system regularly which means draining all the coolant out of the system and filling it with a good quality alkaline flushing solution. Run your engine at normal operating temperature for 15 to 30 minutes with the heater turned on to ensure that the whole system is cleaned. Drain the entire system including the heater core and overflow recovery bottle and then rinse it through with clean water. A thorough clean will require several fill/drain operations.

After flushing you need to perform a stray current check to see if any electrical current is making its way into the radiator. Stray current in the system can kill a radiator in as little as six weeks, particularly in newer cars with aluminium units. The method consists of filling your radiator with clean water (no additive), connecting the negative lead of a multimeter to the negative terminal of your battery, and immersing the positive lead of your meter in the water without allowing it to touch any part of the radiator. Then each electrical component on the car has to be switched on one by one. As this is done you must watch for any voltage readings on your meter. If you get a reading of more than 50mV there’s an electrical problem that needs rectification.

Don’t mix your drinks

After the current check, mix in a quality cooling system additive. Norm says he uses the Castrol product but that any of the formulations from major oil companies will do the job properly. They are, in his opinion, all well researched products. For aluminium radiators, he says genuine GM coolant from VN onwards has proven to be a good thing. However, it doesn’t matter how good the quality of additives are, you must never mix them. There are no coolant additives from different manufacturers that are compatible with each other.

Photograph 13 above shows corrosion. This is a real problem when different metals come into contact. Even though the fins are pure copper, tubes have both copper and zinc in them, solder has lead and tin and combining all these dissimilar metals means electrolysis will occur no matter what. As the fins corrode and lose their mechanical strength, they allow the tubes to expand slightly increasing their susceptibility to splitting. Eliminating stray current goes a long way toward slowing down the process of electrolysis.

Combating Cavitation

Cavitation is one of the biggest problems in a cooling system. It’s caused by poorly-designed coolant pump impellors which create low pressure pockets in the coolant resulting in rapid formation and collapse of air bubbles. Such is the violence of this phenomenon that it destroys metal at a horrible rate. Photographs A-C of a standard Cleveland pump running at various speeds on a test rig demonstrate just how bad things can be.

The solution to cavitating inefficient pumps is shown in photograph D. Melbourne company Ecotrans has special impellers cast to replace pressed steel factory units. The new impellers are fitted with careful attention to running clearances and the actual pump housings are also modified. This one is from a big-block Ford but there are versions available for most popular motors. If you’re having cooling problems your pump could definitely be the cause.

If you are starting to experience the summer time cruising blues, give Aussie Desert Cooler a call on 03 9465 8806 to get your problems sorted out.