An abridged version of an interesting article by Robin Phipson of the Jaguar Car Club which may make you think twice before putting anything other than tap water in the radiator of your TC.
(The full article can be found in the MGCC Johannesburg Centre News Magazine December 1996)

The heat produced when petrol burns in an engine is dissipated as follows:-

Crankshaft Power 25%
Exhaust Gas 35%
Cooling Water 20%
Radiation Losses 20%

We are concerned with getting rid of the 20% of heat produced in the cylinders by hot cylinder gases at temperatures up to 1650°C and transferring this heat by conduction and convection to atmosphere at say 25°C, by the engine cooling system. Considering that aluminium, as in the pistons melts at 650°C and that cast iron, as in the cylinder walls melts at 1530°C it is vital that this heat is removed.

Note that heat and temperature are not the same. A small mass of metal heated to a high temperature can have the same heat content as a large mass heated to a low temperature.

Solids transfer heat by conduction and different solids have different rates of conduction, as a general rule metals are good conductors of heat and non metals such as paint, rust, scale, salt deposits etc are poor conductors of heat. Liquids transfers heat by convection, a process by which heat is transferred by movement within a heated liquid, the transfer of heat through a viscous fluid, e.g. glycerine, is much slower than through a less viscous liquid such as water.

Let us see how the heat of combustion has to get from over 1000°C inside the cylinders to 25°C in the atmosphere.

1. Convection through the combustion gas itself.

2. Convection to the Cylinder wall and carbon layer on piston top and cylinder head surfaces.

3. Conduction from the carbon layer (poor conductor) to the engine metal.

4. Conduction through engine metal.

5. Conduction into the layer of rust, scale and salts on the metal in the water jacket.

6. Convection through the cooling water.

7. Conduction into the paint on the radiator tubes and fins.

8. Conduction into the metal of the radiator tubes and fins.

9. Conduction into the paint on the radiator tubes and fins.

10. The heat on the outside of the radiator is now conducted to atmosphere by the cooling outside air blowing through the radiator

If you thicken the non-metallic layer inside the water jacket (i.e. rust, salts, scale etc) you have more resistance to the flow of heat, combustion chamber temperatures rise and cooling water temperatures rise. Pistons fail and radiators boil in these conditions. So, what has this got to do with radiator additives? Everything.

You may recall that in the early 70's Ford recommended that a can of Bar's Leaks be added to the cooling system on a regular basis, whether there were leaks or not. After a while they found that they were getting piston failures. Research indicated that cylinder wall temperatures were going sky high when this stuff was added.

Ford did further research and found that every radiator additive on the market, whether it was leak stop, anti freeze, corrosion inhibitor, summer coolant or water pump lubricator, increased cylinder wall temperature when added to the cooling water. They approached Ciba-Geigy, the result was Motorcraft SXC103, a corrosion inhibitor only which did not increase cylinder wall temperature.

The second problem with radiator additives containing anti-freeze is that they cause leaks. Anti-freeze has incredible "creep-seep" properties and usually if the car is a bit old, even if well looked after, you add the muck and you soon find this green oozy seep coming out of various joints all over the place including the cylinder head gasket. The real fear is what you can't see, anti-freeze leaking from the water jacket into the combustion chambers and oil ways at the head gasket.

The third problem with radiator additives is that most of the claims on the side of the can are misleading and can lull you into false hapiness.

1. Most anti-freezes "require" a hugh anti-freeze percentage. The higher the percentage the more harm, you only need the absolute minimum.

2. Summer coolants do not "prevent overheating. As an antifreeze reduces the freezing point all the summer coolant additive does is increase the boiling point. If the engine is going to overheat it WILL, it just maybe won't boil, but it will still overheat.

3. Just how does an additive "lubricate the water pump"? All the muck is really doing, apart from rotting the radiator hoses and slowing down heat transfer, is putting a bit of slime on the pump shaft water seal which was designed to run in water in the first place.

The worst additive of all is one which has "leak seal" properties. The gunge causes a hugh increase in metal and coolant temperatures as it deposits itself everywhere inside literally sealing heat in. Have you ever wondered why so many anti-freezes either have a "leak-stop" additive or recommend using one as well? The anti-freeze causes leaks which then has to be sealed.

CONCLUSIONS

1. Use Motorcraft SXC103 (available from Ford dealers) and follow the directions on the container.

2. Use anti-freeze only if you have to and use the absolute minimum. Drain it out, flush and continue SXC103 treatment as soon as freezing conditions are over.

3. Never use leak sealants, fix the leak instead. This is the worst muck of all.

4.Unless it is a straight corrosion inhibitor don't believe a single word from the salesman or the side of the can unless independent scientific proof can be produced.

5. The oil, fuel, water additive market is one of the biggest cons in the motor industry aimed mainly at ripping you off whilst making you feel good.

6. Unless it can be proved otherwise (scientifically), you are on good ground by assuming that all radiator additives cause or encourage leaks and/or cause rises in metal temperature and/or rises in cooling water temperatures.

7. Use clean tap water only in the radiator (with corrosion inhibitor of course). Some people advocate using rain water or distilled or de-mineralised water. This is a fallacy and in the long term does more harm than good. The reason is rather complex but basically, a deposited thin layer of mineral salts in the water jacket protects it to a certain degree from corrosion, if you now add de-mineralised water, it tries to regain its equilibrium with the salts and the deposited salts actually re-dissolve back into the water, exposing the metal surfaces to corrosion.

8. Next time you paint your radiator, think what you are doing ..... locking the heat in. Rather strip all the old paint off first (old brake fluid sprayed into the core does a good job) and then spray on a very thin layer of matt black paint.

Robin Phipson