Engine Cooling

VOL 20/NUMBER 3

ENGINE COOLANT

Blake Urban of Aberdeen, South Dakota, wrote to me to say that he had recently been re-reading old issues of MGA! and wished to correct some misconceptions in thermodynamics relative to cooling systems. I am not sure that the points Blake makes differ from anything that I have written, but he summarized them so well that I thought they were worth repeating.

Point One:
Raising the boiling temperature of a coolant does NOT increase the coolant’s efficiency to absorb or dissipate heat. If an engine operates at 180 degrees pressurized at seven pounds, it will also operate at 180 degrees unpressurized. However, a pressurized system will have a greater margin of safety, about 20 degrees, from boiling than an unpressurized system. By raising the boiling temperature of the coolant, the engine can operate at a higher temperature safely. If the coolant temperature is higher, the temperature difference between the coolant and ambient air temperature is increased, thus increasing the efficiency of the radiator. Raising the boiling point increases the efficiency of the system; it does not lower operating temperatures.

Point Two:
Antifreeze may raise the boiling point of the coolant, but again does NOT increase its ability to transfer heat. In fact, if the concentration is over 30 percent glycol, the efficiency of the coolant decreases. The following is a quotation from The World of Automobiles: An Illustrated Encyclopedia of the Motor Car; Tom Northey, editor; copyright Orbis Publishing Limited, London, 1974. The author of the section on cooling was L.J.K. Setright.

“The effectiveness of a water-cooling system may be improved by raising the (boiling) temperature of the coolant; the introduction of ethylene glycol was originally based on its boiling point being very much higher than that of water. It is a troublesome fluid, however, and experimental work showed that, by pressurizing the cooling system to about 40 lbs per sq. in., water could be kept liquid at the same temperature (about 130 degrees C) without boiling. Some glycol could be retained as an antifreeze agent, but more than 30 percent is undesirable. Water is a better coolant than any other liquid at the same temperature, so superior is its heat transfer ability. Indeed, the higher the boiling point, the better does water compare with any other liquid coolant in this respect, so that adding even a small amount of water to glycol makes it a lot better. By the time the proportions reach 70per cent water/30 percent glycol, heat transfer is virtually as good as with plain water. ”

To Summarize:
Pressurizing the system and adding some glycol raises the boiling point of the coolant and will allow the engine to operate safely at higher temperatures. As long as the coolant doesn’t boil, the engine should be able to easily withstand an additional 15 degrees of temperature. Only when the coolant boils do you develop steam pockets. Steam trapped in pockets, doesn’t absorb much heat when compared to water, and that is when the damaging hot spots develop.

Based on other information in the same article, the following should be observed:

• Ethylene glycol should not exceed 30 percent unless needed for more freeze protection. This is actually enough to keep the system from freezing solid at any temperature, but the coolant turns to slush at low temperatures and will not flow for winter driving. If the system needs more rust protection, add a rust inhibitor or change the fluid more often.
• If the car has an original bellows type thermostat, replace it with a wax pellet type. At pressures above 4lbs./sq. in., the bellows do not function properly due to the pressure.
• Block most of the water bypass shut to prevent water from flowing through the bypass and not to the radiator. Some circulation is usually needed to get the thermostat to operate properly. The original bellows type did this automatically.
• Removing the thermostat may or may not lower engine temperatures depending on how fast the coolant flows in the system. The engine reaches optimum operating temperature sooner and remains constant if the thermostat is left in.

ENGINE COOLING

I have responded a number of times to inquiries concerning MGA cooling, or lack of, particularly in the summer months. Most recently, Dennis Werner wrote from Raleigh, North Carolina, to say that in spite of his best efforts, he continues to have overheating problems when temperatures go over 90 degrees during the North Carolina summer. He appears to have no problem at highway speeds, but the engine coolant temperature quickly rises to 212 degrees or higher if he is hung up in traffic.

Dennis says that he is running with a 7 psi radiator cap so, with the addition of antifreeze in the cooling system, the boiling point of the coolant should be quite a bit higher than the 212 degrees Fahrenheit of plain, unpressurized water. As Blake Urban points out above, as long as the coolant does not boil, heat transfer is taking place, and no permanent damage should be done to the engine. However, if the engine temperature is over 200 degrees and the outside air temperature is over 90 degrees, the cockpit of an MGA is a pretty uncomfortable place! So it might be advantageous to try to reduce the engine temperature at low or stopped speeds.

Unfortunately, “overheating” is a perennial MGA problem, and I have dealt with the subject from various aspects over the past several years. Dennis asked “Could I have a water pump problem, and how could this be checked?” The water pump is probably not the problem unless the impeller is obviously badly worn, the impeller is slipping in the shaft, or the fan belt is loose. Other than checking for these fairly obvious symptoms, I know of no way to check the operation of the water pump.

Dennis’s second question was “Would the addition of an oil cooler be of any benefit in reducing the engine temperature?” An oil cooler will provide some benefit, more in improved lubrication at high engine temperatures than the reduction of overall engine temperature. Engine heat is generated by combustion in the cylinders, and the water jacket around the cylinders is designed to carry the heat away through the transfer of that heat to the flowing coolant. An oil cooler is not going to do much to help transfer the heat away from the combustion process, but will help mitigate the effects of that heat being transferred to the lubricating oil.

ELECTRIC COOLING FAN

As a final question, Dennis Werner asked “Would the addition of an electric cooling fan be an option?” For Dennis’s problem, I would say that an electric cooling fan is an excellent potential option. The fact that his MGA runs at a reasonable temperature at highway speeds indicates that the overall cooling system is probably in good shape, and sufficient air is passing through the radiator by virtue of the car’s speed. At low speeds and at idle, however, insufficient cooling air is drawn through the radiator by a slow moving fan.

Fitting an electric fan to my MGA has been on my list of things to do for some time now, but I have yet to get around to doing it. I have an MGB after market electric fan and a J.C. Whitney generic 10 inch fan, either of which I am sure will do the job. Also, I believe that the regular MGA parts suppliers offer one specifically for the MGA. Electric fans come either with or without a thermostatic control. A thermostatic control is preferable, and it is usually inserted into the top radiator hose. Without the thermostatic control, an activation switch must be installed in the car to turn the fan on manually whenever the temperature is observed to be too high.

Dennis also questioned if the MGA generator-charged electrical system could handle the addition of an electric fan. I do not know for sure, but I expect that the intermittent use of a fan, which probably draws between five and ten amps, is within the capacity of the basic MGA electrical system, particularly if the battery is in good shape. However, if it turns out that the fan runs a lot, particularly when at other than low speed or idle, then it may prove to be too much for the standard MGA electrical system, and the fitting of an alternator should be considered.

While on the subject of cooling fans, Blake Urban, in his letter, also added the following comments concerning the original equipment belt-driven fan in the MGA. “If the fan is mounted backwards, the air does NOT flow backwards through the radiator as some may have implied. For the air to flow backwards the fan would have to run in the opposite direction! What happens (if the fan is installed backwards) is the efficiency is reduced because the MGA’s blades are arched. If you look carefully at the fan you will see that when properly mounted, the initial angle of attack is low, and gradually increases. This prevents cavitation of the air. When mounted backwards the angle of attack is greater, which increases the probability of cavitation. If the blades were flat, the fan could be mounted either way. I haven’t tried it experimentally, but removing the fan may improve cooling at highway speeds. It has been found that in some vehicles traveling at highway speeds, the fan actually impedes air flow through the radiator because of turbulence.”

I agree with Blake’s comments. To install the fan the correct way around, look carefully at the pictures in the manuals. You will see that the central hub and the six flanges to which the blades are attached are at the front; i.e., toward the radiator. Also, as Blake says, it is possible that the fan may impede air flow at highway speeds. This will occur if the road speed of the vehicle is forcing air through the radiator faster than the speed of the fan would normally draw it. This is why more modem vehicles than the MGA that still use a belt-driven fan have a clutch incorporated into the fan hub. The clutch is designed such that it will cause the rotation of the fan to stop when overcome by the force of air passing through the radiator due to the road speed of the car. Thus, an electric fan that will cut off at highway speeds may be a sensible and practical alternative to the original clutchless mechanical fan in the MGA.

COOLING SYSTEM SOLUTIONS

Well, I know of no “cure-all” solutions to MGA engine overheating problems, but I have suggestions. Personally, I feel that most perceived overheating problems can be cured with a clean block and radiator, a correctly maintained cooling system and a correctly tuned engine. If the cooling system itself has any built-in limiting factors, they are related to the way the water circulates in the block and head and the efficiency of the water pump factors which are beyond the control of the average MGA owner. So, if you are having problems with engine cooling, take some time to check out the entire system, and replace or rebuild any components that are not doing their job.

Radiator
The radiator must be clean and in good condition and able to withstand a 15-20 lb. pressure test. Over the years, radiators can become slowly blocked with crud that cannot be removed by flushing with a garden hose. A partially blocked radiator can be a major contributor to overheating. If you have any doubt about the condition of your radiator, take it to a good radiator shop and have it checked out. They will probably boil it out and give it a pressure test. If it fails the pressure test, then a new radiator, or new core, is the only real solution. Repaired radiator cores are only a quick-fix, and will probably let you down when it is most inconvenient. An efficient cooling system needs maximum flow through the radiator. If the boiling out performed by the radiator shop still leaves a coating of scale in the tubes, the shop may remove the header tank and “rod out” the tubes. If all of the tubes cannot be successfully opened up, then again a new radiator or core is the only solution. If you do resort to a new core, you might discuss with your radiator man the possibility of the use of a modem, higher efficiency, higher capacity core.

Air Flow
No matter how good a condition a radiator is in, it cannot do its job unless air can pass through it to cool it. If you have a new radiator, or are sure that it is in good condition, do not forget to clean out the bugs, leaves and other debris that may be stuck in the core. Use a garden hose or high pressure air line. Check the grille at the front of the car. Bent grille slats, badges and driving lamps can all restrict the air flow to the radiator. It is possible to twist the grille slats a little to improve the air flow around and between them.

Also, be sure that you have the original air hoses to the carburetors and the heater in place. If those holes in the radiator bulkhead are left without the air hoses attached, a significant amount of the cooling air can be diverted around the radiator instead of through it.

Engine Block
Like the radiator, the cooling passages in the engine block and head must be clear and clean. The best time to clean the water passages in the engine is when the engine is being rebuilt. If you rebuild your engine yourself, be sure to remove all of the freeze plugs before you take the engine to the machine shop, and have the block and head thoroughly cleaned in a hot dip tank. Before installing new freeze plugs or re-assembling the engine, be sure to thoroughly blowout all water passages in the block and head with high pressure air. If you entrust your engine rebuild to someone else, be sure that they pay particular attention to cleaning out the water passages in the block and head. If you don’t have any plans to rebuild your engine any time soon, flush out the engine with a garden hose. The heater hose connections are a good place to connect the garden hose.

Engine Tuning
A badly or incorrectly tuned engine can certainly contribute to engine overheating. Incorrect ignition timing, either advanced or retarded, can cause the engine to run hotter than normal and, under hot running conditions, can be the cause of burned valves or pistons. Keep your engine, both ignition and carburetors, in correct tune and replace or rebuild any component that prevents the correct tuning.

Radiator Cap
A correct and working radiator cap will maintain the cooling system pressure at seven pounds per square inch, which will raise the boiling point of the coolant by 20-25 degrees F. Be sure that you have the correct cap and that the seal and spring are in good condition. A new cap is not very expensive; so if in doubt, buy a new one. The correct cap has a pressure rating of seven pounds per square inch, and is about one inch deep. The average cap in use today is shallower than the one for the MGA, and will not. seat and seal, so be sure to buy the correct one. If your old cap was not sealing and providing any pressure, be sure your cooling system will stand the pressure of a new one. Check all hoses for excessive softness or hardness and for cracks, and replace as necessary. Check the radiator and hoses for leaks after the new cap has been installed and the engine has been run up to operating temperature and pressure.

Thermostat
A correctly operating thermostat is essential for an efficient cooling system. If a thermostat has failed in the dosed position it will let you know very quickly because the coolant will boil and large amounts of water and steam will be blown out. Failure in the open or partially open position is a little more subtle. A permanently open thermostat will cause the engine to take a long time to warm up. This may not be a bad thing in the summer, but in the winter damage may be caused to the engine if it never reaches the correct operating temperature. Also, the heater will never put out any hot air. A permanently, partially open thermostat will restrict water circulation and may well cause engine overheating in the summer. If you have any doubt about the age and condition of your thermostat, replace it. They don’t cost very much, but they perform a very critical function. The manual recommends a thermostat rated at 160-170 degrees F. For year round use, I would recommend the 170 degree. If you only use your car in the summer, then a 160 degree thermostat may be better.

Personal Observations
My own personal opinion is that the basic design of the MGA body is a primary contributor to hot running. The frontal design is such that, when the car is moving, the air tends to be deflected smoothly around the front, bypassing the radiator grille. Some studies have shown that the recessed MK II grille deflects this flow somewhat and can improve running temperature by five to ten degrees. So, after attention to the radiator, I think that my paragraph above on air flow is the most important. I recently had a call from Warner Baines of Texas (or Maine, depending on the season) to say that he had rigged an auxiliary radiator, made from air conditioning condenser, under the passenger floor of his MGA, and that he picked up ten to fifteen degrees of additional cooling on the highway. The auxiliary radiator was connected into the cooling system in place of the heater. Such a claim; all other things being equal, indicates to me that the MGA circulatory system is probably adequate, and that the limiting factor is the radiator; either for air flow or water flow, or both.

In his discussion, Blake Urban pointed out that a critical part of engine cooling is the transfer of heat from the metal of the engine block to the cooling fluid, with plain water being a better transfer agent than antifreeze. Although I have no personal experience, I understand that there is a product on the market called Water Wetter, or something like that. Water Wetter is added to the cooling system fluid, presumably in addition to antifreeze, to improve the transfer of engine heat to the coolant. I heard some discussion of Water Wetter at the Winston-Salem GT last year, and those who tried it claimed that their MGAs ran noticeably cooler. I haven’t checked on the availability of Water Wetter, if that is what it is called, but I believe that Moss is, or was, offering it. Also, if it is that good, it should be available in auto parts stores. Next, time I am in Pep Boys I’ll check it out.