If you're making more grunt you need more engine cooling. The internal combustion petrol engine is a pretty inefficient beast. To stay cool, it needs to get rid of a lot of heat to the atmosphere. In fact, of all the power that the engine gets from burning fuel, about half is given away through the exhaust and radiator. But that means that if your engine develops a lot more power than standard, you also have to get rid of a lot more heat.
So what can you do to improve the cooling system without spending a motza of cash?
Seal it Up
Before you do anything else, make sure that the standard system is working as well as it possibly can. Firstly, all of the gaps around the radiator core should be sealed off. If the air can find its way around the core - rather than through it - then the flow of cooling air will be reduced. The easiest way of filing these gaps is to use strips of foam rubber. Black foam can be bought for the purpose, or any old foam - from an old seat cushion, for example - can be used and painted black with a spray can. Use contact adhesive to glue the strips into place around the core, making sure that the fins themselves are not obscured.
Duct Season
Next, make sure that all the air entering the grille has an easy path to the core. Place sheet metal or fibreglass guides so that the air has a smooth path to the radiator. This is technically known as making a ducted radiator, and will also improve the car's aerodynamic efficiency. Note that it's not the size of the grille opening which is so vital, but how you get the air from there to the cooling core.
Black Beauty
You want as much heat from the core to be transmitted to the air as possible. Black surfaces dissipate heat much better (and absorb it too - it's a two-way process) than bare aluminium or copper surfaces.
In fact, a perfectly black surface will get rid off 14 times as much heat as an unpolished aluminium surface, and 1.5 times as much heat as an oxidised copper surface. With radiators made from these two materials, it makes sense to make sure that the radiator stays as black as possible. A can of matt black spray paint will work wonders.
Exit Air
What people often forget is that the huge flow of air that passes through the grille and then through the radiator has to come out somewhere. If the air can't get out from behind the radiator, it will build up. This will create a high pressure area, preventing the full airflow through the radiator. In most cases, the air that has passed through the radiator escapes past the engine block and out under the car. If you're using a large front spoiler with a deep undertray extension that comes back under the engine, some of this flow output will be restricted. Easiest in this situation is to fit bonnet vents. To work effectively, a bonnet exit vent needs to have louvres which face backwards, so that the air gets sucked out from under the bonnet by the flow of air over the top of the vent.
Reduce the Load
Firstly, fitting a thermostat which opens a bit earlier will give the standard cooling system a better chance at knocking off the peak temps. But make sure that the engine doesn't then stay too cool - this will upset the engine management system and lead to increased wear. Secondly, in a car with an auto tranny, remove the transmission oil connection to the radiator and instead fit a large separate cooler. Doing this will take the heat load of the tranny off the radiator. Tranny cooler prices from accessory shops are ridiculously high; instead use an old car air conditioning condenser core, or source a used household air conditioner condenser. Finally, use a good quality coolant so that the pump doesn't get clagged like shown here....
Fan Mail
Using a new electric fan to push more air through the core can help. This is especially the case where the car gets hot in slow moving city traffic (where your aerodynamic mods aren't going to make much difference because there's not much airflow anyway).
The cheapest way to turn the fans on and off is to use a temperature switch which is available from the electronics suppliers, RS Components. The cat no 228-2579 switch triggers at 90°
C, for example. RS has stores in most states and countries (check your telephone book) and they stock a couple of switches which will do the job. The best part is that they cost only about A$10 each.
Bigger Core
If after all of that you've still got cooling problems, it's time to go the next step and get a bigger radiator. You can get a radiator shop to make up one that is the same height and width, but has another row of cooling tubes and so is thicker. Alternatively, you can head off to the wreckers with the measurements of your standard core in hand. If you can find a rad from a hi-power car that fits in the standard hole, your life will be made easier. Don't forget to note the location of the hose connections when you're making your selection, though!
Conclusion
Start off by optimising the cooling system that you've already got. If you get overheating in slow traffic, fit electric cooling fans. If the problem occurs in all situations, fit a bigger radiator.
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