Cooling Systems

The cooling systems job is to get the engine up to operating temperature as fast as safely possible and keep it there. It is also responsible for transferring heat from the engine to the heater core for passenger comfort. As combustion occurs, intense heat is produced. Without a cooling system this heat would eventually overheat and damage the engine.

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Air Cooled Engines

Some older automotive engines relied on air alone as its only source of cooling. They had fins on the engine that acted as a heat sink which allowed heat to be transferred into the passing air. They may also have an oil cooler which used the airflow to cool the oil being pumped around the engine. They may also have a fan to generate airflow when the vehicle is stationary or the engine is revving high. These engines typically run much hotter than liquid cooled engines. To provide heat to the cabin, heating ducts took air from the engine compartment, (sometimes near the exhaust manifold) and pumped it into the cabin. Yes, that does mean that if their was even a minor exhaust leak, it would be pumped right into the cabin.

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Water Cooled Systems

Water-cooled systems are used in almost every modern vehicle. This is because water/coolant absorbs heat much better than air. Water can also be pumped around the inside of the engine much closer to where combustion takes place.

LC basic cooling

Different cooling systems will be setup to meet the demands of the engine but all cooling systems rely on the same basic principles. The coolant is pumped through the engine to pick up heat. When the thermostat is closed the coolant is only circulated through the engine, heater core and (usually) oil cooler. When the engine is up to operating temperature, the thermostat starts to open and allows coolant flow through the radiator, which cools the coolant. The thermostat regulates coolant flow through the radiator and by doing that it regulates engine temperature.

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The Two Main Types of Cooling Systems

As the coolant heats up, it expands. This creates a large amount of pressure in the cooling system. This isn’t always a bad thing. For every pound of pressure in the cooling system, the boiling point of the coolant is raised by about 3°F (1.8°C). However, when this pressure becomes too high, it must be bled off to avoid damage to the plastic components in the cooling system. Manufacturers can use 2 different ways of doing this.

  1. Conventional Cooling system: This system is much more common and can be identified by its rad cap. When the engine coolant heats up and creates excessive pressure in the rad, the spring loaded rad cap bleeds off coolant to the reservoir (also called expansion tank) until an acceptable pressure is attained in the radiator. When the engine is shut off and the cooling system begins to cool down, the coolant begins to contract. As this happens, a slight vacuum is created, the rad cap then allows coolant to return to the cooling system
  2. Fully pressurized Cooling System: This system was first used by VW. This system has no rad cap and the pressurized coolant reservoir is part if the main coolant circuit. The reservoir cap is responsible for regulating cooling system pressures. As pressure gets excessive the reservoir cap bleeds off air until system pressure is acceptable.
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Coolant

Coolant must be able to withstand temperatures slightly higher than waters normal boiling point (100°C/212°F) and temperatures much colder than waters normal freezing temperature, (0°C/32°F) for use in all climates. Coolant is usually mixed 50/50 with water. This gives the best balance of freezing point and boiling point. Some coolants come premixed and others do not so you need to read the label before filling. Coolant that is green is called ethylene glycol. The reason many manufactures got away from this is because it is poisonous as well as sweet tasting. If spilled or left out, animals will drink ethylene glycol and die. Newer systems use propylene glycol, it is not sweet tasting and is much less poisonous. However, it is still not safe to drink no matter how many times your buddy dares you. Propylene glycol can come in many different colors, other than green. Do not mix the two kinds of coolant, it can turn the entire cooling system an awful color and the next person that works on the engine may think there is a problem.

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Coolant Pump

CL coolant pumpThe coolant pump or water pump, pumps coolant around the system. The coolant pump is usually driven by the crankshaft by a belt although some newer manufactures are using electric waterpumps to better regulate coolant flow. All modern coolant pumps are centrifugal type pumps, meaning they pull coolant in the middle of the impeller and use centrifugal force to fling coolant outward. Machined into the block are passages for the coolant to go, called coolant jackets or water jackets.

 

 

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Radiator

CL radThe radiators job is to transfer heat from the cooling system to the air that passes through the radiator. Radiators sit at the front of the car behind the front bumper and just behind the A/C condenser. When the vehicle is stationary there is no airflow through the rad so when the coolant gets too hot the rad fans come on to create air flow and regulate coolant temperature.

 

 

 

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Rad Fans

AC rad fanWhen there isn’t enough airflow through the radiator to regulate coolant temperature, the engine will get too hot. Some rad fans are mechanically driven by the engine and some are fully electric and some systems have one of each type. Electric rad fans can be single stage, dual stage and variable speed. The fans are usually controlled by the coolant temperature sensor, PCM or by a separate thermo-switch. When the coolant gets too hot the rad fans come on to pull more air through the radiator and cool the coolant.

 

 

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Thermostat

CL thermostatThe thermostat usually sits neat the coolant pump inlet and blocks coolant flow from the radiator. As the engine gets hot, a wax pellet in the thermostat starts to expand, opening the thermostat, causing coolant to flow through the radiator and cool the engine. As engine temperatures change, the wax pellet in the thermostat changes size to regulate coolant flow and control engine temperature.

 

 

 

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Oil Cooler

CL oil coolerThe oil cooler is a heat exchanger between the lubrication system and the cooling system. It has coolant and oil passing through the same component, but of coarse the two do not come into direct contact. Coolant heats up faster than oil so the heat from the cooling system is used to bring the oil up to operating temperature. Once the oil is up to temperature then the actual cooling begins. Coolant absorbs some of the heat from the oil system which regulates oil temperature.

 

 

 

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Coolant Flange

CL flangeThe coolant flange is where coolant flow gets divided up. These pieces can be plastic or aluminium. They also may or may not be where the ECT or engine coolant temperature sensor is located.

 

 

 

 

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Heater Core

HVAC heater coreThe heater core sits behind the firewall or bulkhead, inside the cabin of the car. Its job is to transfer heat from the engine coolant to the air that enters the cabin when heat is selected by the operator. For more on heater cores check out our HVAC page.

 

 

 

 

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Hoses

CL hoseCoolant hoses must deal with heat, pressure, engine vibrations/movement and weathering. They usually have an inner rubber layer, some kind of reinforcement and an outer rubber layer. The upper rad hose must deal with coolant when it is at its hottest in the system. They are sometimes made a little stronger than the lower rad hose, which only deals with coolant that has been cooled by the radiator.

 

 

 

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Coolant Temperature Sensor

CL ECTThe coolant temperature sensor is a sensor that sits in coolant flow to sense coolant temperature. These sensors are usually NTC (negative temperature coefficient) meaning their resistance goes up as temperature goes down. They sensors may only inform the PCM of coolant temperature or they may activate the rad fans.

 

 

 

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Lubrication Systems

The purpose of the lubrication system is to provide clean engine oil to all moving components in the engine, under pressure. Oil is used to avoid metal to metal contact and to prevent engine wear. The oil acts like a cushion between metal surfaces. If there was no metal to metal contact in an engine, there would be no wear and engines would last forever. The oils secondary purpose is to cool engine internals. Without oil, engines would only run for a few minutes before seizing up and becoming a big pile of broken. This is why oil is so important to an engine. Oil must be delivered at the right pressure. Not enough pressure means that not enough oil will reach wear surfaces, too much pressure and oil will just skim through and not lubricate properly. Optimal oil pressure can be very different for different applications.

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Wet Sump System

A wet sump system is used in most automotive applications today because it is the cheaper system to make, and it does a good enough job for about 95% of everyday driving situations. In a wet sump system the oil pan is used as an oil reservoir for oil that is not currently being used to lubricate the engine. The oil pump creates a low pressure area in the oil sump which pulls oil up through the sump. The pump then pushes the oil under pressure through the oil cooler (if equipped), oil filter and finally to the head and bearings. When the oil has passed through the bearings or valvetrain it is allowed to flow back to the oil pan. The cylinder walls are lubricated by the crankshaft splashing oil up onto the walls alone. It is also worth noting that while the oil is in the pan, it can be cooled by air passing under the vehicle. Some cars have a full belly pan to prevent this and others keep the pan open to encourage this.

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Oil Sump

CL sumpThe oil sump sits near the bottom of the pan so when the vehicle takes a hard corner or accelerates/brakes suddenly and the oil is pressed to one side of the pan, the sump remains submerged in oil and can continue to supply the pump with oil. The sump has a screen in it to prevent large pieces of debris or other contaminates from getting to the oil pump.

 

 

 

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Oil Pump

CL oil pumpThe oil pump is responsible for pulling oil up through the sump and supplying the bearings and other moving engine parts with pressurized oil. Just after the oil pump is the pressure relief valve. Since the oil pump is driven directly by the crankshaft, if engine RPM gets too high, oil pressure may also get too high, resulting in oil just skimming by engine bearings and not lubricating properly, or in extreme cases, lifter pump up. The pressure relief valve is spring loaded and set to open at a predetermined pressure. When this valve opens, oil is bled off back to the pan which regulates oil pressure.

 

 

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Oil Filter

CL oil filterThe filter does its best to clean the oil but many contaminates get by anyway and remain in the oil system, this gets worse as the filter gets old. Dirt and debris are extremely harmful to engine bearings which have very close tolerances. That is why changing the oil and filter is so important.

 

 

 

 

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Oil Pressure Switch

CL oil switchThe oil pressure switch is placed in the oil system to monitor oil pressure and inform the operator that oil pressure is unacceptable. The problem is that oil pressure changes with heat and engine RPM. It is because of this that these sensors are set to switch the oil light on only when oil pressure reaches near zero. Usually by the time the light comes on, damage has already been done to the engine.

 

 

 

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Oil Cooler

CL oil coolerThe oil cooler is a heat exchanger between the lubrication system and the cooling system. It has coolant and oil passing through the same component, but of coarse the two do not come into direct contact. Coolant heats up faster than oil so the heat from the cooling system is used to bring the oil up to operating temperature. Once the oil is up to temperature then the actual cooling begins. Coolant absorbs some of the heat from the oil system which regulates oil temperature.

 

 

 

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Dry Sump System

CL dry sumpA dry sump system is used on high performance applications. In this system, oil that had returned to the pan or bottom of the engine is pumped to a separate reservoir before being pumped to the engine bearings. It is not uncommon to see these systems holding 10+ litres/US quarts of oil, even on a smaller engine. This system offers several advantages. Since the bulk of the oil is not stored in the pan, the engine can sit lower in the vehicle. This lowers the vehicles centre of gravity. Also, the oil capacity can be as much as the engineers want. Any vehicle that is expected to make hard corners and fast acceleration or braking, would benefit greatly from a dry sump system. Since the oil is stored in a separate oil filled container with a pump on the very bottom, no matter how hard of a turn the driver takes, the pump will never pull in air like in a wet sump system. This is the main reason why this system is used.

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