LEST WE FORGET

Most of us have experienced overheating with our old cars and talked about this very common problem with other enthusiasts. I have owned seven old cars, English and American, from the twenties to the seventies, all of which have had overheating problems, which were overcome in various ways. What follows is an outline of the techniques which I have found will cure or prevent the problem without band aids such as electric fans, which, being visibly non-original, should only be tried if these methods are insufficient, but more on that later. My Mark IV Jaguar, a model renowned for overheating, will cruise at 55mph on 73 degrees C in an ambient of 35C. If I get stuck at a series of traffic lights on a steamy 35C Brisbane day, the temperature will slowly rise towards 80, however this rise can be slowed significantly by temporarily increasing the idle to 1000 rpm with the hand throttle. Of course when the temperature in the shade is 35C, the cabin of a Mark IV will feel like the fresh air is being supplied from the radiator fan, and really you should be sitting in an air conditioned living room sipping a cold Chardonnay!

So let’s assume you are doing a restoration or at least removing the head and water pump. If not you will have to alter the following sequence of remedial measures.

The Radiator Don’t waste your time- get a new core! Pressure flushing will not adequately clear blocked tubes, because the little particles will have agglomerated and stuck to the tube walls. A less effective but lower cost alternative to a new core is to remove top and bottom tanks and rod the tubes, providing the rods are a neat fit in the tubes, [a piece of wire is not good enough]. Also, rodding is not an option with honeycomb cores. But hey, if you’ve removed the tanks you might as well fit a new core. [Be sure you make an accurate drawing of the mounting dimensions first, or …..!!] Find a radiator repairer who knows about heat transfer principles and get the best core you can. But note that increasing the core thickness by adding a row or rows of tubes can be a trap, because at idle your fan may pull less air through, but more on this later.

The Engine Water Passages Often this is left to the machine shop’s agitated wash tank but this is not nearly good enough for old, neglected engines i.e. the ones we find! In fact, other cleaning is essential for any engine which has not had coolant water with inhibitor installed and maintained since it left the factory. Before the block and head go to the shop, shove high pressure water, bits of wire, bent toothbrushes etc into every water hole, welsh plug and passage way; you will be surprised at how many grains of corroded iron you will flush out as well as sludge. If the block stays in the car you can do near as good a job if take the head off, [yeah, do the valves as well!]; even better if you remove and replace the welsh plugs.

Prevention Is Better Than Cure Your cooling system is now as clean as you can get it but it won’t stay that way! No Sir! Little grains of corroded iron and other crud will continue to break away from the walls of the water passages and stick in the radiator tubes, eventually causing a return of overheating. Put a fine, conical shaped screen in the radiator top inlet to catch these particles; I use 30 or 40 denier panty hose toes, folded back to be clamped between the hose and the inlet stub. A brass mesh will be better when I work one out. [And you can tell your spouse the panty hose legs are excellent for tying plants to stakes!]. After fifty miles inspect your screen and then adjust the inspection interval according to the amount of crud you have collected.

The Thermostat Got one installed? As well as maintaining temperature they are particularly useful for restricting the water flow rate, so that over about 45 mph, [when the water pump is delivering a really strong flow], the water has sufficient residence time in your super efficient new radiator to cool down. Standard practice in 1920’s cars without thermostats was [and is] to fit into the top hose a disc with a 5/8" hole to provide some head for the pump, but a thermostat is better. You can get 50mm diameter 71C thermostats at most parts shops, [a 76C one would probably be better in a cold climate], and these can be adapted to fit somewhere in the top hose area. Even if you have a hose as small as 32mm ID you can grind away almost all the perimeter of a 50mm thermostat and it will fit inside the hose at an angle. If the thermostat does not lie at an angle, you will need to drill a 3/16" hole in it to allow some bypass during warm up. If, as in the Mark IV Jaguar, you have a fancy thermostat with a bypass to the water pump inlet to provide fast warm up, it probably doesn’t work, and so it is safest to block the bypass hose and fit a new thermostat, [with a bypass hole], into the old housing.

The Water Pump Even a pump with corroded vane tips [with resulting increased clearances in the casing] will be good enough over about 25mph [say 1250 rpm] but you really need efficiency at idle. So get it rebuilt; an impeller with an extra vane can help at idle, and indeed may even have been used on later models of your engine.

The Fan In the world of fluid dynamics the fan works the same as the centrifugal water pump, so it is only really needed from idle to 25 mph. Cars post about 1960 have shrouds around the fan to ensure it must suck air through the radiator, rather than bypass through the gap between the core and the blades. You can achieve a significant improvement in bypass losses by fabricating an aluminum spacer ring to fit between the fan and its pulley. Uniformly machine out as much metal as possible to avoid unbalancing the fan. A gap of 5/8" between the leading edge of the blades and the core is good, but you need to check how you can remove the fan belt. For my Mark IV Jaguar the spacer is 13/16" thick, which results in an air gap of 5/8". This modification has proved very effective at idle, and, being almost unnoticeable, still appears original.

Bypass Air From the seventies on manufacturers began fitting foam rubber around the radiator to fill the gap between it and the mudguard inner panels; this is often missing but is essential as it prevents air which enters the grill from taking the path of least resistance through this gap, rather than through the core. There may be scope on earlier cars to stop this bypassing.

If All Of This Is Not Enough I have not had to do more than the above on any cars I have had, including a Mark II Jaguar, another model with a marginal cooling system for Brisbane summers. However there are other more marginal cars, and in such cases the answer is a thicker radiator core [i.e. more tubes] and a thermostatic electric fan to move the air through it. This is the proper solution where there really is a design inadequacy. Band aid type solutions such as fans with more or longer blades and larger diameter fan pulleys should not be necessary if all of the above have been done, and indeed can cause other problems with fan bearings, metal fatigue, and excessive air turbulence [cavitation] at higher speeds. In fact viscous fluid couplings and electric fans were introduced to overcome these unnecessarily high air flows at speed.

A Side Benefit To Consider Around two thirds of the energy in petrol is converted to heat; engines with large sump capacity can remove some of this heat via the oil [hence finned sumps], however most of it has to be removed by the cooling system. [This of course is the reason why the engine heats up when climbing a long hill on full throttle at a reasonable speed, and cools down so quickly going down on almost closed throttle.] Therefore lower fuel consumption means less demand on the cooling system, so tune your engine and ensure the distributor centrifugal and vacuum advance are functioning correctly, as these have a significant effect on fuel consumption. I recently installed electronic ignition with a high voltage coil on my 1937 LaSalle, [these have the Cadillac side valve V8], and controlled tests showed a 13% improvement in fuel consumption. I also noticed it ran cooler [the ambient was unchanged at 31C] and, having previously calibrated the temperature gauge, I know that the reduction was 4C. The electronics are entirely inside the distributor, the coil looks normal, so the conversion does not detract from originality, and I’m therefore intending to do the Mark IV Jaguar. Of course 4C won’t solve any serious overheating problem, but at high ambient temperatures it gives a bit more margin.