FYI Excellent General Info & Various Tests

Arv

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Hi All:

Thought this link is very good source of general info for our community, so I will post it.

http://www.familycar.com/Classroom/CoolingSystem.htm
http://www.familycar.com/Classroom/

I am also posting some of the things I have extracted for a quick read.

Head Gasket Diagnosis:

One way to tell if a head gasket has failed is through a combustion leak test on the radiator. This is a chemical test that determines if there are combustion gases in the engine coolant. Another way is to remove the spark plugs and crank the engine while watching for water spray from one or more spark plug holes. Once the technician has determined that a head gasket must be replaced, an estimate is given for parts and labor. The technician will then explain that there may be additional charges after the engine is opened if more damage is found.

Coolent Tank Pressure Cap:

When the cooling system pressure reaches the point where the cap needs to release this excess pressure, a small amount of coolant is bled off. It could happen during stop and go traffic on an extremely hot day, or if the cooling system is malfunctioning. If it does
release pressure under these conditions, there is a system in place to capture the released coolant and store it in a plastic tank that is usually not pressurized. Since there is now less coolant in the system, as the engine cools down a partial vacuum is formed. The
RADIATOR CAP on these closed systems HAS A SECONDARY VALVE to allow the vacuum in the cooling system to draw the coolant back into the radiator from the reserve tank (like pulling the plunger back on a hypodermic needle) There are usually markings on the side of
the plastic tank marked Full-Cold, and Full Hot. When the engine is at normal operating temperature, the coolant in the translucent reserve tank should be up to the Full-Hot line. After the engine has been sitting for several hours and is cold to the touch, the coolant
should be at the Full-Cold line.

The National Automotive Radiator Service Association (NARSA) recommends that motorists have a seven-point preventative cooling system maintenance check at least once every two years. It consists of:

* a visual inspection of all cooling system components, including belts and hoses
* a radiator pressure cap test to check for the recommended system pressure level
* a thermostat check for proper opening and closing
* a pressure test to identify any external leaks to the cooling system parts; including the radiator, water pump, engine coolant passages, radiator and heater hoses and heater core
* an internal leak test to check for combustion gas leakage into the cooling system
* an engine fan test for proper operation
* a system power flush and refill with car manufacturer's recommended concentration of coolant

Let's take these items one at a time.

Radiator pressure cap test:

A radiator pressure cap is designed to maintain pressure in the cooling system at a certain maximum pressure. If the cooling system exceeds that pressure, a valve in the cap opens to bleed the excessive pressure into the reserve tank. Once the engine has cooled off,
a negative pressure begins to develop in the cooling system. When this happens, a second valve in the cap allows the coolant to be siphoned back into the radiator from the reserve tank. If the cap should fail, the engine can easily overheat. A pressure test of the radiator cap is a quick way to tell if the cap is doing its job. It should be able to hold its rated pressure for two minutes. Since radiator caps are quite inexpensive, I would recommend replacing it every 3 years or 36,000 miles, just for added insurance. Make absolutely sure that you replace it with one that is designed for your vehicle.

Thermostat check for proper opening and closing:

This step is only necessary if you are having problems with the cooling system.
A thermostat is designed to open at a certain coolant temperature. To test a thermostat while it is still in the engine, start the engine and let it come to normal operating temperature (do not let it overheat). If it takes an unusually long time for the engine to warm up or for the heater to begin delivering hot air, the thermostat may be stuck in the open position. If the engine does warm up, shut it off and look for the two radiator hoses. These are the two large hoses that go from the engine to the radiator. Feel them carefully (they could be very hot). If one hose is hot and the other is cold, the thermostat may be stuck closed.

If you are having problems and suspect the thermostat, remove it and place it in a pot of water. Bring the water to a boil and watch the thermostat. You should see it open when the water reaches a boil. Most thermostats open at about 195 degrees Fahrenheit. An
oven thermometer in the water should confirm that the thermostat is working properly.

Internal leak test:

If you are losing coolant, but there are no signs of leaks, you could have a blown head gasket. The best way to test for this problem is with a combustion leak test on the radiator. This is accomplished using a block tester. This is a kit that performs a chemical test on the vapors in the radiator. Blue tester fluid is added to the plastic container on the tester. If the fluid turns yellow during the test, then exhaust gasses are present in the radiator.

The most common causes for exhaust gasses to be present in the radiator is a blown head gasket. Replacing a bad head gasket requires a major disassembly of the engine and can be quite expensive. Other causes include a cracked head or a cracked block, both are even more undesirable than having to replace a head gasket.

When a head gasket goes bad:

The process of replacing a head gasket begins with completely draining the coolant from the engine. The top part of the engine is then disassembled along with much of the front of the engine in order to gain access to the cylinder heads. The head or heads are then
removed and a thorough inspection for additional damage is done.

Before the engine can be reassembled, the mating surfaces of the head and block are first cleaned to make sure that nothing will interfere with the sealing properties of the gasket. The surface of the cylinder head is also checked for flatness and, in some cases, the
block is checked as well. The head gasket is then positioned on the block and aligned using locator pegs that are built into the block.

The head is then placed on top of the gasket and a number of bolts, called head-bolts are coated with oil and loosely threaded into the assembly. The bolts are then tightened in a specific order to a specified initial torque using a special wrench called a torque wrench.

This is to insure that the head gasket is crushed evenly in order to insure a tight seal. This process is then repeated to a second, tighter torque setting, then finally a third torque setting. At this point, the rest of the engine is reassembled and the cooling system is filled with a mixture of antifreeze and water. Once the engine is filled, the technician will pressure test the cooling system to make sure there are no leaks.

In many engines, coolant also passes between the heads and the intake manifold. There are also gaskets for the intake manifold to keep the coolant from leaking out at that point. Replacing an intake manifold gasket is a much easier job than a head gasket, but can still take a couple of hours or more for that job.

Engine Fan Test:

--- para deleted because of limitation of charactors for the post ---

A temperature sensor determined when the engine was beginning to run too hot and turned on the fan to draw air through the radiator to cool the engine. On many cars, there were two fans mounted side by side to make sure that the radiator had a uniform air flow for the width of the unit.

If the air conditioner was turned on, a different circuit would come into play. The reason for this is the air conditioning system always requires a good air flow through the condenser mounted in front of the radiator. If the air flow stopped, the air conditioned air coming through the dash outlets would immediately start warming up. For this reason, when the air conditioner is turned on, the fan circuit would power the fans regardless of engine temperature.

If you notice that the engine temperature begins rising soon after the vehicle comes to a stop, the first thing to check is fan operation. If the fan is not turning when the engine is hot, a simple test is to turn the AC on. If the fan begins to work, suspect the temperature sensor in the fan circuit (you will need a wiring diagram for your vehicle to find it). In order to test the fan motor itself, unplug the two wire connector to the fan and connect a 12 volt source to one terminal and ground the other. (it doesn't matter which is which for this test) If the fan motor begins to turn, the motor is good. If it doesn't turn, the motor is bad and must be replaced.

In order to test the system further, you will need a repair manual for the year, make and model vehicle and follow the troubleshooting charts and diagnostic procedures for your vehicle. On most systems, there will be a fan relay or fan control module that can be a
trouble spot. There are a number of different control systems, each requiring a different test procedure. Without the proper repair information, you can easily do more harm than good.
 


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