What to put in a Radiator?

Yes, you should have an additive, not just water, in your radiator. But you do need to decide why you need it, and what type to use. In other words, what is the potential problem you are trying to avoid.

Is your car overheating, and you want a product to help it run cooler?
or
Do you live in an area where the temperature drops below zero, and you want to stop the "coolant" from freezing?
or
Neither of the above, but you want to slow down corrosion inside the engine.

Sorry to get technical, but you firstly need to think about what the liquid in your cooling system needs to do. When the spark plug fires and the petrol burns, heat is produced, some of which is transferred to the metal (cast iron in this case) of the cylinder head and engine block. That heat is absorbed by the liquid which is pumped around the engine and to the radiator. There the liquid has to give up its heat to the tubes and fins in the radiator, where the passing air carries the heat away.

So primarily, you need a liquid that is efficient at absorbing and releasing heat.

Pure water is one of nature's most efficient transmitters of heat. Water absorbs heat quickly and releases it quickly. That's why we use it to cool engines. But it does have a few failings.

Our engines typically run at around 80 to 90 degrees C. At 100 C water will boil away, leaving you with no liquid to transmit the heat away from the engine. The radiator cap pressurises the system and this raises the boiling point, to perhaps 110 C before the water boils away. But if your car runs hot (eg: highly modified, radiator in poor condition, hot climate etc) then you can easily exceed 110 C on a bad day.

Secondly, water is unique in that it expands when it freezes. (If it didn't, fish in ponds would be frozen solid when the water froze from the bottom up!) If you live in a cold climate where the engine could get below 0 C, then the water in the engine will freeze, expand, and crack the cylinder head and/or block. Not recommended.

And thirdly, water with some impurities (eg: tap water) will conduct electricity. Since your engine is cast iron, but the water pump (and heater tap) are aluminium, the water will assist in the electrolytic corrosion of the aluminium. The water pump will corrode away from the inside.

OK, so you need to add something to the water, but what.

The most common additive is Ethylene Glycol (commonly called just Glycol). All the bright green bottles of "coolant" that you see at Repco, Auto One, Target etc contain Ethylene Glycol. Glycol is an excellent anti-freeze and you need to use it in a cold climate. It will also raise the boiling point of the water, and the higher the concentration of Glycol in the radiator the higher it will raise the boiling point. And it is a good corrosion inhibitor. The problem is, Glycol is a lousy conductor of heat - it has half the thermal conductivity of water. ANY Glycol in the radiator will cause the engine to run hotter. The more Glycol you use, the hotter the engine will run. I know one guy who had no water, just 100% Glycol, and he explained why he needed it, because the engine always ran at 110 C. We drained out all the Glycol, flushed the radiator, put in tap water, and the engine ran at 85 C. He didn't need ANY Glycol. Glycol is also an extremely slippery substance, sufficiently so that it can find its way past engine gaskets. We have a number of customers with green stains down the side of the engine block where the Glycol has worked its way past the head gasket.

If your engine is overheating, lets say it often exceeds 100 C, then you have a problem you should investigate. Adding Glycol is like sticking a bandaid on a broken arm. It might make you feel a bit better, but it hasn't solved the problem. Forget the radiator flush stuff you buy, pull the radiator out and have it professionally serviced. It will cost you no more than $100. Make sure you have the best radiator fan available. Make sure the fan is on the right way around.

And if you have neither overheating nor freezing problems, avoid Glycol. There are a few other product on the market that are not anti-freeze, nor do they increase the boiling point of the water, but they do actually make the engine run cooler. Typically they help remove surface corrosion on the cast iron, which helps the heat to transfer faster into the coolant. My favourite is Penrite SIN Racing Coolant as it works well and is only $10 or so for 500 mls, which is all you need in the radiator. In extreme circumstances, there is a product called Water Wetter, which claims, on the bottle for all to see, that it "improves the heat transfer by 50% and your engine will run cooler". It is about $30 for the bottle, but I have used it in race car engines, and it works.

Hope that helps, and avagoodday
Colin