Cooling System Theory

ADX 150 – Engine Repair

ADX 170 – Climate Controls

Purpose

Normal operation produces heat that must be carried away by coolant

Cooling system transfers heat to cooler outside air when engine is hot.

Cooling system keeps heat in the engine when engine is not warm enough.

Modern cooling systems are designed to maintain an even temperature of about 180 to 230°F (82 to 113°C).

Cooling System Operation

System design removes 35% of total heat.

If not equipped with factory A/C, cooling system is usually not able to handle additional heat load of aftermarket units.

Components

COOLING SYSTEM COMPONENTS• Water Pump

• Cooling Fan

• Radiator

• Pressure Cap

• Thermostat

• Clamps and hoses

• Overflow tank

Water Pumps

Centrifugal Type Water Pump. Inlet comes from bottom of Radiator. Outlet is through impeller to engine. Water Pump Replacement can be due to

leaks or bearing failure. Transfer pump parts and use correct

gaskets.

Weep Hole

Coolant will often leak out of the weep hole.

This indicates the shaft seals in the water pump have failed.

Water pump replacement will be required.

Water Pumps

Water pumps can be driven off of the serpentine belt, the timing belt, or the camshaft.

When driven off of the timing belt, most technicians suggest replacement when replacing the timing belt.

Water Pumps

Water Pumps

Radiators

Allows for heat to move from coolant to the outside air.

Cooler air flowing through the radiator cools the coolant.

Most radiators about 28-35 sq. feet. Can have multiple cores to increase area. Two types…

- Cross flow- Down flow

Radiators

Radiators

Radiators

Many radiators will have oil coolers built into them.

These can be for the engine oil or the ATF.

Should either of these crack, oil could get into the coolant and coolant into the oil.

Coolant Expansion Radiator pressure results from the

expansion of the coolant as the engine warms up.

A small amount of air used to be kept in the radiator to allow for this expansion.

Since air leads to rust and corrosion, the radiator needs to be filled completely with coolant.

The pressure cap and coolant reservoir work together to allow for this expansion.

Pressure Cap

The upper gasket prevents coolant from escaping to the outside. The lower gasket keeps a pressure in the radiator. The cam lock pushes the two gaskets against the sealing surfaces when the cap is installed. The safety stop prevents the cap from being opened too quickly.

Pressure Cap

Pressurizing a liquid increases the boiling point of that liquid.

Cooling systems are pressurized so that the boiling point of the coolant is raised.

Many cooling systems are pressurized to 15 psi.

The coolant’s boiling point increases about 3° F for each psi increase in pressure.

Pressure Cap

The pressure cap allows the pressure to build, and release past a specified point.• Equipped with Vacuum and Pressure Valve

• Used to raise Pressure in system

Pressure Cap

Pressure Cap

Pressure Cap

The pressure cap also improves the operation of the water pump.

By keeping the radiator pressurized, the water pump has a constant supply of coolant to draw from.

If pressure became too low, the coolant would boil and the water pump would draw only air.

Overflow Tank

Contains reserve coolant. When cap releases coolant due to

coolant expansion, coolant goes to overflow tank.

When cooling system cools off and creates a vacuum, coolant is pulled from overflow tank.

Overflow Tank

Some closed cooling systems do not have a cap on the radiator.

The overflow tank is pressurized with the rest of the cooling system.

The coolant level will be checked in the overflow tank.

Pressurized Tanks

Systems with a pressurized overflow tank keep a small amount of air in the tank.

This allows the coolant to expand and compress the air.

Most tanks like this will have a pressure cap on the tank and no cap on the radiator.

Pressurized Tank

Odd Cap Location (Durango)

Opening a Hot System

Slowly turn the cap with a rag and do not turn it past the safety lock.

Thermostat

Speeds up engine warm up. Regulates flow and temperature of engine

coolant. Most are on the outlet side of coolant flow. Maintains optimum engine operating

temperature for best emissions and economy.

Thermostat

Thermostat temperature is the opening temperature

Thermostat should be fully open 20°F above opening temperature

195°F thermostat = fully open at 215°F

180°F thermostat = fully open at 200°F

Thermostat

The thermostat contains a wax pellet on the engine side of the thermostat.

Wax melts and expands when engine heats up.

As the wax expands, it overcomes spring pressure and opens the valve.

Thermostat

Thermostat

Thermostat Bleeder

Some thermostats have a “jiggle pin” that should be installed at the top to aid in bleeding air from the system.

Clamps and Hoses

Hoses direct coolant from the engine to the radiator, heater core, and the overflow tank.

Clamps hold hoses in place.

Clamps

PowerGrip Clamp

PowerGrip clamps are larger than the hose and must be heated to shrink and seal the hose.

Hoses

Preformed hoses are made specifically for an application.

Flex hoses are used for a variety of applications.

Some lower radiator hoses contain a spring to prevent them from collapsing due to water pump suction.

Coolant Flow

The water pump pumps coolant through the block.

If the thermostat is closed, coolant flows through the block, heater core, and the thermostat bypass.

The bypass leads back to the water pump.

There will be no flow through the radiator when the thermostat is closed.

Thermostat

When the thermostat is closed, coolant is directed back into the block through the bypass passage.

Coolant Bypass

Some thermostats are designed to block off the bypass passage when they are open.

Coolant Flow

When the thermostat is open, coolant is then allowed to flow from the block to the upper part of the radiator.

The coolant is then cooled in the radiator. The water pump draws the coolant out of

the bottom of the radiator so that it can then be circulated throughout the block to cool the engine.

Water Jackets When an engine cylinder block and head are

cast, cavities called water jackets are formed around the cylinder walls and combustion chambers.

These water jackets allow coolant to circulate around the very hot areas, including the exhaust valve seats, as well as the relatively cooler areas of the lower cylinders.

The coolant absorbs heat from the hot areas and transfers this heat to the colder areas in the engine or radiator.

Water Jackets

Coolant Flow

Coolant Flow

Some manufacturers position the thermostat on the inlet side of the water pump.

As the cooled coolant hits the thermostat, the thermostat closes until the coolant temperature again causes it to open.

This reduces thermal cycling (expanding and contracting of the metal).

Thermal cycling can damage aluminum engine components.

A modern style cooling system showing how the coolant flows through the block first, then through the cylinder head, and finally through the radiator after the thermostat opens.

Block Heaters

Block heaters are small, electrical-resistance heater units that can be mounted in the block.

These heaters are plugged into ordinary 110-volt ac outlet and are used in very cold areas to warm an engine while it is shut off.

Block heaters provide easier engine starting and faster warm-up, especially for diesels.

Block Heaters

Typical block heaters install in one of the core plug holes.

Aftermarket Block Heaters

Aftermarket block heaters generally should not be installed in late model vehicles.

The computer checks the ambient air vs. the coolant temperatures after sitting for several hours.

If the two disagree, the MIL will illuminate and a DTC will set.