Cooling Systems
 

We will review the purpose and operation of each component and then discuss methods of tune-up/maintenance.

A cooling system consists of: the radiator, radiator cap, overflow tank, water, pump, thermostat, fan assembly, fan shroud, hoses and the coolant. ( The water passages inside the engine block technically are part of the system, but other than cleaning them during an engine overhaul, there is no practical method of changing their operation.)
 

The radiator’s main function is to transfer the head generated in the engine to the surrounding atmosphere. It contains a large quantity of small water passage tubes and interconnecting fins, and as hot water passes through the tubes, some of the heat is radiated into the air passing between the tubes. A secondary purpose of the radiator is to provide storage for the needed volume of water required to cool the engine in question. The radiator cap on a system without an overflow tank has two purposes: To keep the water from spilling out, and to increase the atmospheric pressure within the cooling system. You will recall that water boils at temperature of 212 degrees at sea level, but as the pressure decreases, water boils at a lower temperature. Conversely, when pressure is increased, the water will boil at a higher pressure. Thus, we have caps rated at various pressures; 15# with most factory systems, (245 degree boiling point) but lower pressure caps are available. When/if the pressure inside the system exceeds the rated cap pressure, a sprint inside the cap releases and lets water flow out. If an overflow/recovery system is used, the cap has an additional function. After water has flowed from the radiator to the recovery tank, the temperature inside the engine cools, the pressure drops and tends to suck the overflow water back into the engine. The cap will allow the reverse flow back into the engine. Thus, the engine cooling system will remain full of coolant, rather than a combination of air and coolant, which improves overall cooling.
 

The water pump moves the water from the engine to the thermostat assembly. If the thermostat is open, the water passes through the radiator and back into the engine. Whether thermostat is open or closed, the pump also circulates water through the heater core and back into the engine.

The thermostat is a temperature sensitive switch that controls the flow of water to the radiator. It’s only function is to allow coolant to pass through when the coolant temperature equals or exceeds it’s rated temperature, and to stop coolant flow if the temperature is below the rated level. The thermostat controls only the minimum system temperature! If the system is operating normally and is adequate for the engine in question, the coolant temperature will remain in the general range of the thermostat rating. However, switching to lower temperature thermostats will not improve system cooling, but simply transfers coolant to the radiator at a lower temperature. If the system is marginal or inadequate, the coolant temperature will increase regardless of the thermostat rating.

The fan assembly is designed to move air through the radiator during stops or low speed operation. After a speed of approximately 30 mph is reached, the fan has little effect on the system cooling. The fan shroud, when properly located, insures that all air generated by the fan assembly actually passes through the radiator. 

Hoses transfer the coolant to and from the radiator and the heater core. The coolant ideally contains a 50-50 mix of antifreeze and water. The 50-50 mix will transfer heat better than any other combination of water and antifreeze.

What can be done to make the cooling system work better? Most importantly, keep the radiator clean both inside and out. Occasionally spray high pressure water both directions through the radiator to dislodge bugs and other debris from it. Also use soapy water to remove grease or other contaminants from the exterior. The inside? Have it manually cleaned by a capable radiator shop. Under no circumstance use use chemical cleaners in your cooling systems (unless you plan to replace the water pump). Such cleaners are designed to cut grease and they do. You can be absolutely assured that in about 6 weeks of normal driving after using a chemical cleaner, you will replacing the water pump, because the cleaner will remove the lubricant /sealer on the water pup shaft packing. That results in squealing and coolant leakage. DO use the water pump lubricant/anti-rust mixtures after the antifreeze mixture has been in the system more than 2 years.

A factory temperature actuated clutch fan is the most efficient and least power consuming type of fan available. The centrifugal type clutch and all types of flex fans do not cool as well as original equipment type units. Keep the belt only tight enough to prevent slippage. Overtightening will cause excess wear on the water pump bearings.

The fan shroud should fit closely against the radiator and should extend to about the center of the fan blades. (The blades should be about half in and half out of the shroud for maximum cooling efficiency.)

There are differences in thermostat quality and it pays to buy a brand name unit such as Gates. Hoses should be closely watched for deterioration and replaced as needed.

If you have an old or fragile radiator in use, consider lowering the cap pressure to 7 ½ #. This lowers the maximum pressure in the radiator and minimizes it’s tendency to leak and will extend it’s life. The boiling temperature will be reduced to about 230 degrees, but that normally does not cause a cooling problem.
 
 

Troubleshooting Cooling Systems

The following was prepared for a 455ci engine, but generally applies to all Pontiacs.

The basic problem is that we are trying to cool 455+ cubic inches of engine with a engine cooling system that is adequate for about a 350 engine. As Pontiac increased the displacement, the water passage became smaller, and the heating load became larger. Sure, Pontiac redesigned the cooling passages, but the fact is that since the block size never varied, the internal cooling is not optimum. Consider that all aspects of the engine cooling system are identical for a 350 and a 455, although the 350 will have far less heat to load. That is why boring a 455 may add to the cooling system problems. More cubic inches are generating heat but there is less metal in the cylinder walls to absorb and dissipate the heat to the remainder of the engine block.

Another extremely important aspect of cooling is the relative efficiency of the engine. All engines waste a very large percentage of the potential power of fuel combustion to heat in the block, water and air. The more efficient an engine actually is, which translates into wasting less heat, the cooler the engine will run. In other words, the less throttle needed to maintain the desired speed, the less heat that is wasted into the cooling system. We will discuss this in more detail later.
 

1. Identify the times and conditions under which the cooling is inadequate.

1. Problems in normal temperature during city driving?
2. Problems at normal open road driving
3. Problems at idle

Open road driving problems are not usually caused by inadequate air flow. As higher RPM causes a higher heat load for the system, defective radiator, incorrect water flow rate (either too fast or too slow), and engine can all contribute.

To if the water is flowing too fast or slow at highway speed, shift to second and maintain the same speed. This reduces the load on the engine, speeds up the water flow, increases air flow through the radiator, and it dumps even more heat into the water. If this maintains for increases in temperature, you probably need to slow down the water flow, improve the radiator, or improve engine efficiency. If the temperature drops, you may need to increase water flow rate.
 

War Stories

As the performance of my wagon was increased and different parts were tried, the wagon ran hotter on the open road. A large radiator from a Chevy 454 was adapted, and it helped some. A new quality temperature controlled clutch was installed with the fan that helped some. The engine has always been highly tuned and very efficient, so that was not a fixable item. I saw an add for the high flowing Robertshaw thermostat and tried it: That was the real key for me because the engine ran HOTTER with it. I then recognized that I need to slow down the water flow to allow better water distribution in the radiator thus utilizing it’s larger capacity, and longer time in the radiator to improve heat radiation. The addition engine RPM caused by my 3.55 gear, slightly looser converter, and higher engine output all contributed to the problem. The following steps were taken:

1. Installed a small oil cooler for the transmission thus removing that source of heat from the radiator.
1. Had a 6" crank drive pulley custom made to slow down both the water pump and alternator.
1. Found a larger water pump pulley from a ’77 non air-conditioned Catalina and installed it to further slow down the pump.
1. Modified the pump by reducing the size of the pump fins (thus reducing the pumping capability). Note that most air-conditioned Pontiacs used a less efficient pump to accomplish the same thing. Cast fin impellers can be modified by removing alternate impeller blades, and stamped steel impellers can be changed by reducing the depth of the impeller blades. You may want to find a used or cheap new pump to experiment with.
1. Installed a Gates #5505 160 degree thermostat for summer and a Gates #33008 for winter driving. The Gates seem to have the best combination of adequate but not excessive flow for the 455, and they are quality units.
1. Investigated Water Wetter by talking to the manufacturer, drained anti-freeze, and added Water Wetter for summer use. It does help by 4 to 6 degrees during steady driving. The mixture is replaced with anti-freeze in cold weather.

The net result of these items allows the car to be driven at 2900 RPM in 90 degree weather with the water temperature of 206 degrees as measured with a precision digital thermometer. At the drag strip in 90+ weather, the temperature will reach about 195 at the end of a run, and cool down to about 180 by the time we are back in the pits. I also have a MOPAR K car cooling fan modified to push air installed in front and to the lower left corner of the radiator for cooking when sitting in the staging areas, but don’t normally need it. It has absolutely no effect on cooling at road speeds. 
 

Let’s discuss engine operations. When I was testing intake manifolds, it was noticed that the first three aluminum units (Holley, Torker, and Torker II, all single plane) caused the engine to run 10 degrees warmer. I attributed it to different heat characteristics of aluminum, but when the aluminum Pontiac and Performer units were installed, the temperature was normal. I then realized that the single plane units reduced engine efficiency so much at lower RPM that not only was throttle feel and performance lost, but the engine had to be worked harder with more throttle input to maintain the same speed! That put more heat into the water and caused the temperature to increase at the same RPM. I have also seen many situations where retarded timing, or less than optimum timing caused the temperature to increase for the same reasons noted above.
 

A radical camshaft will tend to cause or increase cooling problems due to the increased overlap and accompanying water of burning fuel into the exhaust system.
 

Improper carb calibration, either too rich or too lean, will also contribute slightly to cooling problems.
 

A friend, Kevin Kirk, who runs a ’71 Chevelle wagon with a 454, won numerous awards as "Racer of the Year" in NHRA Division 5 in ’95. His wagon is race only and not driven on the street, but he had continuous heating problems in just trying to race. He found and bought a 4 row Chevy radiator, but it not solve the problems. He then bought a Griffen aluminum 2 row radiator of about the same height and width. It is so effective that he now has to keep his engine running before a race to keep it from getting too cold. I note that Jeg’s/Summit catalogs have various sizes of this radiator for around $190. Kevin says it is quite soft, and that he found a sizable dent in his, caused by a June bug. I would think it could be used on a driveable car if it were carefully mounted, and a rigid, fairly coarse screen installed in front of it (to shred big, hard shelled bugs).
 

As mentioned in the above comments, engine tuning is much more important in cooling problems than most people suspect, so assure that optimum mechanical timing is found, vacuum advance is used and optimized, and the carb is properly calibrated.