Cooling System Function and Operation part 1
Cooling
If you are concerned by overheating problems that just get worse as you try to remedy them, then this series may give you a better understanding of the cooling system and dispel some common myths about engine cooling. The goal of this series is to touch on each individual component in detail.
The cooling system is the most neglected, least understood, and most fraught with mystery of any part of our cars operation. The many requirements of the cooling system are not always apparent. Some of these include cooling the valves and pistons, both cooling and heating the carburetor, controlling oil temperatures, and providing interior heat for winter comfort. Many people believe the cooling system needs no regular service or maintenance, until they have a serious overheating problem.
Your cooling system is required to remove only about 20% of the total engine generated heat. More than 75% is expelled out the exhaust pipe, leaving 5% escaping to the air through the block and heads in the form of under hood heat. The under hood heat must have a method of escaping under the car, if not it can lead to high temperatures.
Coolant Flow Path
It is important to understand how the coolant flows through the system from one component to the next. These descriptions are directed to V-8 engines in particular, but basic commonality applies to the 6-cylinder engines also.
Starting at the water pump, coolant is drawn/pushed into the pump from the lower radiator hose. This coolant is ideally about 50* cooler than the operating temperatures of the engine. The impeller of the pump pushes the coolant through two passages (one in each bank) exiting through the timing cover (small block and 429-460) into the engine block. The openings into the block allow coolant to flow around the cast cylinders to the rear of the block, where it moves upward via passages in the head gasket corresponding with cored opening into the cylinder heads. The cylinder heads direct coolant flow from the rear to the front of each casting. While along the way, the coolant passes around the valve pockets, valve guides, exhaust ports, and combustion chambers. At the front of the heads are openings directing coolant into the intake manifold from both sides to the thermostat housing. Thermostats have the function of controlling minimum engine operating temperatures by creating flow restrictions.
The upper radiator hose transfers the hot coolant, as the thermostat allows it, to flow to the radiator where heat exchanges into the air as it circulates downward.
Coolant in the lower portion of the radiator is ready to start the cycle over again.
Water Pumps
Water pumps on our Fairlanes are either cast iron or aluminum. The water pump is a simple yet thorough design. The pump is driven by belt through a pulley from the engine crankshaft.
Five components make up the water pump construction. They are housing, shaft, impeller, bearing, and seal.
Housings are machined to accept the impeller/shaft assembly, this being supported by the bearing. Bearings and coolant can not coexist, the seal keeps them apart. An impeller is a round disc of metal with multiple blades or paddles about its circumference. A rear cover plate is bolted to the housing and acts as a wall to keep coolant from escaping the impeller cavity. The housing is machined or cast to allow the impeller to run in close proximity to the housing face, capturing coolant and creating a pressure differential through the pump. This pressure difference causes the coolant to be sucked up on the inlet side and be pushed away through the outlets. Coolant is compressed as it leaves the pump. This is a similar effect as used in vacuum cleaners where vacuum is present to pull up air (with dirt in it) and slightly compressed air is exhausted.
Water pump efficiency is variable according to many factors. Internal clearance and impeller condition can cause reduce flow. Engine revolutions and pulley ratios effect pump speeds. Loose belts slipping on pulleys render the pump ineffective. Flow restrictions elsewhere in the cooling system can slow coolant movement. Restrictions can be clogged or under size radiators, hose collapse, improper thermostat operation, block core debris, impeller erosion, hose cross sectional area, or gasket placement. All of these factors have a cause and a cure to correct them.
Stock water pumps may be modified to improve flow. By removing the rear cover (FE) or separator plate on the (small blocks) a round flat metal disc pop riveted to the back of the impeller will move more coolant at low speed and reduce high rpm cavitation. These kits are available in the after market, should you chose to try them.
Stock water pumps are designed with over capacity capability. They normally can move more coolant than your engine requires. High flow after market pumps will move no more coolant than the system restrictions allow. My opinion is, stock pumps need not be replaced by racing pumps for street use. Most cases of racing pumps used on the street with great improvements in cooling, are attributed to pumps over coming other deficiencies in the system. This assumes that the stock pump you use is of acceptable quality. Many cheap remanufactured pumps are no bargain, having failure rates extremely high, compared to new pumps. While on the subject, I would like to remind you that Ford water pumps are some of the most difficult to change. Even if the grade 2~ 1/4" X 5" bolts do not break off, requiring timing cover removal. If the cheap part has a "Life Time Warranty", how many times do you want to change it, also a fan blade going through the radiator is not normally covered by discount store warrantees.
Ford water pumps are similar except for the FE. The FE does not bolt to the timing cover, but stands off from the block front face. The small blocks do bolt to the timing cover, with a separator plate between them, and having coolant exit passages going through the timing cover.
Ford water pumps have the lower radiator hose casting, two exit ports into the block, and two smaller hose connections near the top. The hose nipple closest to the top is used for the water pump by-pass coolant hose connected to the intake manifold. Its purpose is to allow coolant to circulate through the engine before the thermostat reaches normal operating temperature. Coolant will not flow unless there is a way to get it around the thermostat. An analogy would be having a garden hose connected to the house with the nozzle on the end closed. All though the faucet is open and water pressure is present with out the nozzle open no water can move and is stagnant in the hose. This subject is very important and will be discussed in detail in future segments. The lower hose nipple on the pump is a return port for the heater coolant. After coolant is circulated through the heater it is considerably cooler than engine temperature and is reintroduced to the pick up side of the water pump.
An old pump on your car may look great and have no leakage, but have impeller problems and be unable to move enough coolant. Why would an impeller not be able to pump coolant? One of the impeller problems that reduce pump efficiency is coolant that is in poor condition. Old rusty coolant contains solids that have become a fine grit slurry capable of milling the impeller blades down to the point that they no longer pump. Coolant becomes acidic over time attacking all metals in the system. Acid does eat away at impellers also. Pump impellers can and will separate from the shaft, becoming inoperative. The impeller a pressed fit on the shaft. Poor quality, sloppy rebuilding techniques, or corrosion can allow the impeller to disconnect from the shaft. The result is no pumping of coolant.
This subject is quit involved requiring several segments to complete. If you can hang in there with me you will not be disappointed in the end. Future segments will include detail component and diagnostic discussions covering the following:
Engine block and heads
Intake manifold, carburetor heat, and passenger heater
Thermostat and housing
Water pump by-pass hose
Upper and lower radiator hoses
Fans, pulleys, fan clutches, and shrouds
Radiators
Radiator caps, recover tanks, and overflow tubes
Coolant and its service
Common causes of over heating
Mike the Radiator Man