Cooling System Check-Out and Maintenance

VOL. 16/NUMBER 1

This month we have chosen an article on Cooling System Tune Ups as overheating is always an issue with MGA’s that are driven hard. We have added a second article to go with this on the Cooling Fan Shroud as it seemed appropriate.

Determining the date of first publication for these tech articles is like finding the date of manufacture on an MGA from the chassis and engine number, i.e. it is not a pure science. The current MGA! magazines (2009/2010) are Volume 35, so we estimate the Cooling System article was written around 1991, and the Fan Shroud was written around 1997.

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. (Note 1 from Website Managers – if your radiator still has the original brass plaque on it, remote it before giving your radiator to a rad shop. Also, warn the shop to to over pressure test the radiator – they can distort the top tank).

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 diverted around the radiator instead of through it. (Note 2 from Website Managers – check that you have the felt/horsehair strip fitted to the bonnet above the radiator).

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 when the engine is being rebuilt. If you rebuild your engine yourself, be sure to remove all 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 or re-assembling the engine, be sure to thoroughly blow out all water passages in the block and head with high pressure air. If you entrust your engine rebuild to some one 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, 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. (Note 3 from the Website Managers – a mixture that is too lean can also cause overheating).

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 is 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 closed 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 degree 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.

Cooling System Modifications
Some modifications can be made to the MGA cooling system to improve engine cooling at sustained highway speeds in hot summer weather. However, I should stress that none of these modifications should be treated as a “cure-all” for a poor condition, or poorly maintained stock cooling system.

If you have the radiator re-cored, a heavier duty core with more tubes, if available, might be a good idea. Check with the radiator shop to see if a suitable core is available. I have no experience with the use of a larger capacity radiator, but it may help improve engine cooling. Although, as I stated above, I think the limiting factor is probably the efficiency of the engine block and water pump design.

The tuning manuals suggest removal of the thermostat to improve cooling for Stage IV tuning and above. Removal of the thermostat should increase water flow to the radiator, but the by-pass hole in the thermostat chamber in the head must be blocked off. If the by-pass is not blocked, coolant flow to the radiator may be decreased instead of increased. According to the tuning manual, a sleeve (Part #IIGI76) was available for this purpose. Such a sleeve can be fabricated from a piece of split brass tubing of a diameter that can pushed securely into the thermostat housing to block the by-pass hole. Don’t forget to remove the sleeve and replace the thermostat if you drive your MGA in the winter.

The early MGBs had a larger capacity (13 row) oil cooler than that offered as an option for the MGA. The use of this cooler on the MGA should certainly improve the cooling of the oil which should also improve overall engine cooling.

An electric radiator fan can be installed instead of, or in addition to, the fan on the water pump. The advantage of the electric fan is that it cools the radiator while the car is stopped or moving slowly in traffic, which is a time when any engine is prone to overheating. Electric fans are available for the MGA, and they attach to the radiator core. They can be installed either in front of the radiator or behind. In either case, I would suggest removing the mechanical fan. Whichever side of the radiator you install the fan, be sure to wire it so that it moves air through the radiator from front to back. The electric fan can be turned on either by a switch on the dash, or by a thermostat switch inserted into the top radiator hose. I would recommend buying a fan with a thermostat switch.