Radiator Restoration and Repair

The Model A had a thermo-siphon cooling system.  Coolant is not only pumped through the system, but is also circulated by hot water from the engine block forcing the collar water down through the radiator and back into the water jacket in the block.  All cooling system components must be in good condition to ensure efficient cooling, but in this article we’ll focus on the radiator.

The Model A radiator consists of a top tank and a bottom tank joined by a series of either round or oval metal tubes, depending on the vehicle and year of manufacture.  In operation, the engine-driven water pump supplies water to the top tank which flows through the tubes to the bottom tank and then back to the engine block.  Thin sheet metal fins secured to the tubes serve to dissipate the heat of the water flowing through the radiator.  The system is open to the atmosphere and is not pressurized.

An overflow pipe is soldered to the radiator frame in two places and extends to the bottom of the radiator.  On the ’30-’31 models, there is a hole located in the frame cross-member so that overflow water can fall straight through to the ground.  The ’28-’29 models did not have this hole.  Some “driving” car builders have added a rubber hose extension to the pipe so that overflow water does not drip on the front spring or axle.

The amount of water that can be pumped through the cooling system is determined by how much water the pump can deliver and how much water can actually flow through the radiator itself.  Pump output is dependent on engine speed and under Model A era driving conditions the pump normally did not deliver more water than the radiator could pass.  Times change and today’s Model A can be driven at speeds much faster than were envisioned at that time.  As a result, it’s possible to pump more water at highway speeds than the radiator can handle.  If this happens, the excess water will either flow out the overflow pipe or from under the radiator cap.  When you lose enough water, the engine will overheat.

The original Model A radiator could pass from 38 to 43 gallons per minute (flow rate) depending on tube configuration (the ’30-’31 4 row AA Commercial radiator could pass 48 gallons per minute).  However, over time, several factors conspire to lower the flow rate:

  1. Corrosion and mineral deposits inside the tubes.
  2. Pinched or dented tubes caused by stones or other external factors.
  3. Damaged tubes removed from service by well meaning, but ignorant, radiator service shops.

Another important, and often overlooked, factor is the replacement of a worn-out or damaged radiator with a reproduction type.  In many cases, the “repro” actually has fewer or smaller diameter tubes than the original.  It’s no wonder that the flow rate of some “repros” may be less than 30 gallons per minute.  A conversation with one reproduction radiator manufacturer revealed that he did not even know the flow rate of his product!  For this reason, the Model A owner may be better off restoring the original radiator than installing a reproduction.

A good radiator shop will perform the following steps when rebuilding or repairing an original Model A radiator.

  1. Measure the flow rate before doing anything else.  This can be rechecked later to verify the effectiveness of the repairs.
  2. Use a caustic solution and ultrasonic equipment to thoroughly clean the tanks and tubes.
  3. Replace and repair any damaged tubes, maintaining the original number if possible.  Extensive radiator damage may require that some tubes be pinched off and soldered closed.
  4. Reattach loose cooling fins to the tubes.  A fin not secured to the tube will not dissipate the heat.  In the original radiators, fins were individually soldered to the tubes.
  5. Lightly paint the radiator with special radiator paint to prevent corrosion.  It should be noted that any type of radiator paint or primer will impede heat transfer to the surrounding air but is a necessary evil to protect the radiator.
  6. Check the flow rate of the refurbished radiator.  Remember, a good radiator should be able to pass from 38-43 gallons of water per minute (48 gallons for the ’30-’31 4 row AA Commercial radiator).  Any less could be asking for trouble.

Few radiator shops have the equipment or expertise to measure the flow rate and some will maintain that this is not even necessary.  Actual experience has proved otherwise and it’s worth the effort to find a shop equipped to do this measurement.

Sometimes a simple back flushing of the engine will clear up an overheating problem.  This can be done after the radiator have been thoroughly cleaned.  One precaution should be observed if this procedure is used.  DO NOT use more than five to seven pounds of pressure or the radiator may be damaged.  Original cooling system components were not designed to operate under pressure.

                Some controversial consideration…

The following items are considered controversial by some Model A enthusiasts but in my opinion offer some very real and practical advantages:

  1. Antifreeze coolant – Use of a good antifreeze provides freezing protection if you want to drive your “A” during the winter months.  In addition, the built-in rust inhibitor will help keep your cooling system rust and corrosion free.  Modern coolants also include a special water pump lubricant, which can extend the life of your pump.  In contrast, plain water can promote rust and scale and offers no freeze protection or water pump lubrication.
  2. Thermostats – Any gasoline engine runs better at a constant temperature because the gasoline vaporizes more evenly.  In addition, engines operating at a temperature of at least 165 degrees will evaporate combustion chamber water resulting from the combustion process, helping to prevent rust.  A third benefit provided by the thermostat is to act as a “restrictor” at high speeds and reduce the flow rate through the system.  This can help prevent water or coolant overflow under highway driving conditions.

Incidentally, if a thermostat is installed, a 1/8 diameter hole should be drilled through the valve plate to allow a small amount of water to circulate through the cooling system at all times.  This will ensure that heated water from the block will actually reach the thermostat and cause it to open.  If this is not done, the engine may be running hot and the thermostat will not sense the overheating.

                More controversy…

If you plan to do a lot of driving at highway speeds, you might consider grinding a little off of the water pump impellor ears to reduce the water flow.  This will also reduce flow at lower speeds so it should be done a little at a time.  Grind the ears evenly to maintain impellor balance.  It would probably be a good idea to check out this procedure with friends or fellow club members before you start!

(Note:  Additional information on water overflow and radiator baffles can be found in the April, 1930 Ford Service Bulletins).               

 This tech tip was originally provided by Walt Wawzyniak and printed in the June 2001 and the August 1992 “A” Quail Call.

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