by Dudley Hume (Sept 1992)
As I have mentioned before, no modern engine could run for many minutes without overheating if its cooling system was not pressurised to at least 13 lbs per square inch.
I had a very traumatic experience of this problem with the TR4A engine in the Barracuda. To keep the nose line low I used a Zephyr radiator with its top tank just level with the cylinder head outlet. With the standard TR4A pressure cap at 4 lbs per square inch anything above one third throttle opening caused the temperature gauge needle to move up faster than the speedo needle.
Having eventually fitted a Ford Transit plastic header tank with a 13 lbs per square inch cap and steam bleed tube the problem disappeared. I won’t bore you with details of the failed experiments with brass tanks etc. Before arriving at the final solution. I had also learned that the standard TR4A set up was inclined to boil!
So bearing the above in mind and knowing that most Allard owners have a problem with overheating (As we did when the cars were new in the late forties and early fifties) I have been looking into the simplest, low cost way of reliably overcoming the problem.
The system principle shown in the sketch is now standard practice on virtually all water cooled engines. I have managed to identify a neat, easy to install header tank (a Ford Sierra item).
These are of course, easy to obtain and not expensive. But you can use anything similar from other Ford models or other manufacturers.
The main point to bear in mind is that two steam bleed entries are required in the header tank.
The only tricky part is fixing the steam bleed tunes to the outlet pipes and the return connection to the lower hose.
It is most important that the steam bleed pipes or tubes to no protrude into the outlet pipes at all.
This system works by allowing steam generated by local hotspots (of which are are many in the V8 flat head) to be bled off as it rises up the outlet pipes. It then passes to the header tank and condenses back to water. This means that no water is lost.
This is the main problem with the original cooling system, the steam enters the radiator top tank and leaves by the 4 lb per square inch cap vent so the water volume is reduced and as the water is lost the process speeds up.
As previously mentioned the higher pressure prevailing in the system determined by the 13 lbs per square inch cap (some are 21 lbs now) supresses the boiling point and so the combination effectively prevents overheating.
It is necessary to seal off the existing filler cap in the radiator so it cannot leak at the higher pressure. This can be done with a disc of gasket material trapped between cap and seat, making sure that it does not become split of punctured as the cap is screwed down.
The steam bleed tubes can be made from 10mm or 3.8″ outside diameter bundy tube, which can be curved on the standard fixline, and cut to the required segment length.
Drill a hole in the outlet pipe equal to the inside diameter of the tube, positioned approx. As show in the sketch, and remove all traces of burr from the inside of the hole with a fine rat tail file and make a radiused edge.
Braze the bundy tube to the outlet pipe ensuring it is exactly over the hole.
The hoses between the bleed tubes and the header tank are standard Ford steam hoses cut to the required length. The return connection in the bottom hose can be made by using a brass or steel tube 5/8″ outside diameter by one and a quarter inches long with a rim brazed or silver soldered to one end. This rim must be curved to fit inside of hose. This should now be vulcanised into the hose by a tyre repair specialist.
If difficulty is experienced in assembling the modified hose it is advisable to remove the radiator fixing bolt on that side and push the radiator forward in inch or so. If you happen to have one those screwed fittings for tapping into a hose for a heater connection from way back you may be able to use this instead.
Below is an image kindly supplied by Charles Gough of his custom made silicon hose. We are trying to source more of these so get in touch if you’re interested.
If the foregoing is applied to your car it should result in an end to you overheating problems, if this is what you want of course.