Engine Cooling

by Alan Burgess

One area of concern to many kit car owners is engine cooling as various kits are not developed with the budgets of Ford or Peugeot etc. This can cause over heating problems and maybe poor airflow, cutting holes in the bodywork to allow more air in is one way of getting more air to the radiator, but it would spoil the look of your kit, and be detrimental to the body strength. But airflow is not always the cause, the solution could lie elsewhere. Firstly lets consider why it's overheating and if in fact it is simply the gauge misreading. Is your Merlin is fitted with after market gauges? If so they should have been supplied with a compatible sender unit for the cylinder head. Those kits that use the dash out of the donor usually find they are fitted with a voltage stabiliser to the rear of the dash panel. These gauges should use the temp sender from the donor of the dash panel as they are suitable, if ford based these are colour coded just below the terminal thread either cream, blue, black or red.

There could also be other problems that cause overheating such as too low tyre pressures being used, or a sticking thermostat, or a duff pressure radiator cap or wrong radiator, is the radiator single or double cored? I am not sure if there is a recommended tyre pressure for the Merlin. The higher the pressure the less rolling resistance, but this is at a cost of handling and Safety, but would also rattle those false teeth out! Too Iowa pressure would again be a cause of overheating as well as wondering whether you were going to get anywhere. This would have to be done by trial and error to find out what suites each owner best. The end result will be a compromise between handling, fuel consumption and tyre wear, With my own Merlin, a Sierra based vehicle, the radiator comes from the donor and is quite tall and wide. This is fitted quite some way in front of the engine and laid back at about 45 degrees, which reduces the airflow through it. A baffle plate was recommended by the manufacturer to direct air through the radiator, this was fitted.

Once the car was on the road I experienced my temperature gauge going past the 100 degrees mark and was quite concerned, although the engine when the bonnet was lifted seemed ok. I decided to fit an ordinary radiator from a Capri/Cortina as the engine was only a ohc pinto and put this upright in front of the engine as on the Cortina based Merlin's. This was also fitted with a fixed fan running on the water pump, (not the viscous type but the solid plastic ones) This made a slight improvement, it only runs at 95 degrees now. One thing I did find odd was the temperature gauge, this would become condensed up when on the move and so did the fuel gauge. I also noticed that if I was motoring on a bit, the faster I went the higher the needle on the gauge went, although with more air going through this should have been the reverse.

Deciding to get to the bottom of this I approached the gentleman that runs Premier wiring at this years Newark show, it seems the cause could well be that there is not a voltage stabiliser fitted in the wiring loom. I do not remember seeing one in the loom or fitting one during the build. These reduce the voltage from 12V to around 9V and was the reason for the needle getting higher as the speed increased as more voltages was supplied to the gauge. This also caused the condensation, early gauges were not fitted with voltage stabilisers but I am informed that the newer ones on the market are. The fitting of this may well solve my problem but not everyone's. I have purchased one and intend to fit it in the near future.