AUT 125 - Chapter 21 Coolant System Operation and Diagnosis
bypass
A _____________ around the closed thermostat allows a small part of the coolant to circulate within the engine during warm-up.
belt tension gauge
A __________________________ is needed to achieve the specified belt tension. Install the belt and operate the engine with all of the accessories turned on, to run in the belt for at least five minutes. Adjust the tension of the accessory drive belt to factory specifications or use Chart 21-3 for an example of the proper tension based on the size of the belt. Replace any serpentine belt that has more than three cracks in any one rib that appears in a 3 inch span.
Scan tool method.
A scan tool can be used on many vehicles to read the actual temperature of the coolant as detected by the engine coolant temperature (ECT) sensor. Although the sensor or the wiring to and from the sensor may be defective, at least the scan tool can indicate what the computer "thinks" is the engine coolant temperature.
thermostatic spring
A second type of thermal fan has a ____________________________ added to the silicone coupling fan drive. The thermostatic spring operates a valve that allows the fan to freewheel when the radiator is cold. As the radiator warms to about 150°F (65°C), the air hitting the thermostatic spring will cause the spring to change its shape. The new shape of the spring opens a valve that allows the drive to operate like the silicone coupling drive. When the engine is very cold, the fan may operate at high speeds for a short time until the drive fluid warms slightly. The silicone fluid will then flow into a reservoir to let the fan speed drop to idle.
7,500 gallons (28,000 liters); 2,000 gallons (7,500 liters)
A typical water pump can move a maximum of about _______________________________________ of coolant per hour, or recirculate the coolant in the engine over 20 times per minute. This means that a water pump could be used to empty a typical private swimming pool in an hour! The slower the engine speed, the less power is consumed by the water pump. However, even at 35 mph (56 km/h), the typical water pump still moves about _________________________________ per hour or 0.5 gallon (2 liters) per second!
14 to 16 PSI (97 to 110 kPa)
According to the SAE Handbook, all radiator caps must indicate their nominal (normal) pressure rating. Most original equipment radiator caps are rated at about _______________________________________.
Lack of heat from the heater.
Air rises and can form in the heater core, which will prevent coolant from flowing.
Infrared thermometer method.; As the engine warms, the temperature reaches near thermostat opening temperature. As the thermostat opens, the temperature drops just as the thermostat opens, sending coolant to the radiator. As the thermostat cycles, the temperature should range between the opening temperature of the thermostat and 20°F (11°C) above the opening temperature.
An infrared thermometer (also called a pyrometer) can be used to measure the temperature of the coolant near the thermostat. The area on the engine side of the thermostat should be at the highest temperature that exists in the engine. A properly operating cooling system should cause the pyrometer to read as follows:
212°F (100°C); 257°F (125°C)
At sea level, water will boil at __________________. With a 15 PSI (100 kPa) pressure cap, water will boil at ___________________, which is a maximum operating temperature for an engine.
scroll
Coolant leaving the pump impeller is fed through a __________. The scroll is a smoothly curved passage that changes the fluid flow direction with minimum loss in velocity. The scroll is connected to the front of the engine so as to direct the coolant into the engine block.
0.0045 to 0.012 inch (0.1 to 0.3 mm)
Core tubes are made from ___________________________________________________ sheet brass or aluminum, using the thinnest possible materials for each application.
Deflection.
Depress the belt between the two pulleys that are the farthest apart and the flex or deflection should be 1/2 in.
Step 1 Drain the system (dispose of the old coolant correctly). Step 2 Fill the system with clean water and flushing/cleaning chemical. Step 3 Start the engine until it reaches operating temperature with the heater on. Step 4 Drain the system and fill with clean water. Step 5 Repeat until drain water runs clear (any remaining flush agent will upset pH). Step 6 Fill the system with 50/50 antifreeze/water mix or premixed coolant. Step 7 Start the engine until it reaches operating temperature with the heater on. Step 8 Adjust coolant level as needed.
Flushing the cooling system includes the following steps.
bar; 14.7 PSI
However, many vehicles manufactured in Japan or Europe use radiator pressure indicated in a unit called a _______. One bar is the pressure of the atmosphere at sea level, or about __________.
Drive belt tension Bent fan Fan for balance
If the bearing is defective, the pump will usually be noisy and will have to be replaced. Before replacing a water pump that has failed because of a loose or noisy bearing, check all of the following:
Step 1. Shut off the air conditioning and turn on the heater. The heater will help rid the engine of extra heat. Set the blower speed to high. Step 2. If possible, shut the engine off and let it cool. (This may take over an hour.) Step 3. Never remove the radiator cap when the engine is hot. Step 4. Do not continue to drive with the hot light on, or serious damage to your engine could result. Step 5. If the engine does not feel or smell hot, it is possible that the problem is a faulty hot light sensor or gauge. Continue to drive, but to be safe, stop occasionally and check for any evidence of overheating or coolant loss.
If the coolant temperature warning light comes on, follow these steps.
Heater hoses Radiator hoses Radiator Heater core Cylinder head Core plugs in the side of the block or cylinder head
If the cooling system is free from leaks, the pressure should stay and not drop. If the pressure drops, look for evidence of leaks anywhere in the cooling system, including:
Hot water method.
If the thermostat is removed from the vehicle and is closed, insert a 0.015 inch (0.4 mm) feeler gauge in the opening so that the thermostat will hang on the feeler gauge. The thermostat should then be suspended by the feeler gauge in a container of water or coolant along with a thermometer. The container should be heated until the thermostat opens enough to release and fall from the feeler gauge. The temperature at which the thermostat falls is the opening temperature of the thermostat. If it is within 5°F (4°C) of the temperature stamped on the thermostat, the thermostat is satisfactory for use. If the temperature difference is greater, the thermostat should be replaced.
core tubes; cooling fins
In each of these types, the coolant flows through oval-shaped _______________. Heat is transferred through the tube wall and soldered joint to __________________.
series flow system
In the __________________________, the coolant flows around all the cylinders on each bank. All the coolant flows to the rear of the block, where large main coolant passages allow the coolant to flow across the head gasket. The coolant then enters the rear of the heads. In the heads, the coolant flows forward to a crossover passage on the intake manifold outlet at the highest point in the engine cooling passage. This is usually located at the front of the engine. The outlet is either on the heads or in the intake manifold.
parallel flow system
In the ___________________________, coolant flows into the block under pressure and then crosses the head gasket to the head through main coolant passages beside each cylinder.
Exchange old coolant with new coolant Flush the cooling system Pressure or vacuum check the cooling system for leaks
Many coolant exchange machines are able to perform one or more of the following operations.
Water pump drive belt for tension or faults Cooling fan for faults Heater and radiator hoses for condition and leaks Coolant overflow or surge tank coolant level Evidence of coolant loss Radiator condition
Many cooling system faults can be found by performing a thorough visual inspection. Items that can be inspected visually include:
Marks on the tensioner.
Many tensioners have marks that indicate the normal operating tension range for the accessory drive belt. Check service information for the location of the tensioner mark.
Cross-flow radiators.
Most radiators use a cross-flow design, where the coolant flows from one side of the radiator to the opposite side.
250°F to 258°F (120°C to 126°C)
Most vehicles are equipped with a heat sensor for the engine operating temperature indicator light. If the warning light comes on during driving (or the temperature gauge goes into the red danger zone), then the coolant temperature is about ____________________________________________, which is still below the boiling point of the coolant (assuming a properly operating pressure cap and system).
Low coolant level Plugged, dirty, or blocked radiator Defective fan clutch or electric fan Incorrect ignition timing (if adjustable) Low engine oil level Broken fan drive belt Defective radiator cap Dragging brakes Frozen coolant (in freezing weather) Defective thermostat Defective water pump (the impeller slipping on the shaft internally) Blocked cooling passages in the block or cylinder head(s)
Overheating can be caused by defects in the cooling system, such as the following:
4,000°F to 6,000°F (2,200°C to 3,300°C)
Peak combustion temperatures in the engine run from _________________________________________________________.
Radiator Coolant recovery reservoir Upper radiator hose
Replace the old radiator cap with a new cap with the same pressure rating. The cap can be located on the following:
reverse cooling
Some engines use _______________________. This means that the coolant flows from the radiator to the cylinder head(s) before flowing to the engine block.
series-parallel flow system; bleed holes or steam slits
Some engines use a combination of these two coolant flow systems and call it a _______________________________________. Any steam that develops will go directly to the top of the radiator. In series flow systems, _________________________________ in the gasket, block, and head perform the function of letting out the steam.
Torque wrench reading.
Some vehicle manufacturers specify that a beam-type torque wrench be used to determine the torque needed to rotate the tensioner. If the torque reading is below specifications, the tensioner must be replaced.
surge tank
Some vehicles use a _______________, which is located at the highest level of the cooling system and holds about 1 quart (1 liter) of coolant.
Crankshaft belt Camshaft
Some vehicles use a surge tank, which is located at the highest level of the cooling system, with a radiator cap.
Engine coolant temperature (ECT) exceeds approximately 223°F (106°C). A/C refrigerant pressure exceeds 190 PSI (1,310 kPa). After the vehicle is shut off, the engine coolant temperature at key-off is greater than 284°F (140°C) and system voltage is more than 12 volts. The fan(s) will stay on for approximately three minutes.
The PCM commands low-speed fans on under the following conditions.
Engine coolant temperature (ECT) reaches 230°F (110°C). A/C refrigerant pressure exceeds 240 PSI (1,655 kPa). Certain diagnostic trouble codes (DTCs) set.
The PCM commands the high-speed fan on under the following conditions.
silicone coupling
The ________________________ fan drive is mounted between the drive pulley and the fan.
3°F (1.6°C)
The boiling temperature will increase by approximately _________________ for each pound of increase in pressure.
1,200°F and 1,700°F (650°C and 925°C)
The combustion temperatures will average between ________________________________________________________.
Overheating.
The engine can overheat due to the lack of proper coolant flow through the system.
Down-flow radiators. Cross-flow radiators.
The two basic designs of radiators include:
Serpentine fin core Plate fin core
The two types of radiator cores in common use in most vehicles are:
centrifugal pump; impeller
The water pump is a _______________________ that can move a large volume of coolant without increasing the pressure of the coolant. The pump pulls coolant in at the center of the _____________.
Down-flow radiators.
This design was used mostly in older vehicles, where the coolant entered the radiator at the top and flowed downward, exiting the radiator at the bottom.
10 mph (16 km/h)
To prevent a fan from cycling on and off excessively at idle, the fan may not turn off until the ignition switch is moved to the off position or the vehicle speed exceeds approximately ________________________.
An overheating engine may result from a faulty thermostat. An engine that does not get warm enough always indicates a faulty thermostat.
Two important things about a thermostat include:
One two-speed cooling fan Two cooling fans (one for normal cooling and one for high heat conditions)
Two types of electric cooling fans used on many engines include:
coolant recovery system
When the system cools, the pressure in the cooling system is reduced and a partial vacuum forms. This vacuum pulls the coolant from the plastic container back into the cooling system, keeping the system full. Because of this action, the system is called a _________________________________. A vacuum valve allows coolant to reenter the system as the system cools so that the radiator parts will not collapse under the partial vacuum.