Liquid Cool

6 years ago How-To


The cooling system dissipates the heat from the engine that’s generated from combustion and friction. If this heat isn’t removed, oil film breakdown can result, causing metal-to-metal contact and excessive and rapid wear. The cooling system also provides a secondary feature – heating the passenger compartment. As the coolant passes through the vehicle bulkhead, the air that passes over it is heated and warms the vehicle passengers in cold weather.


The primary purpose of the cooling system is to maintain optimum engine temperature and provide satisfactory performance and emission levels under all expected driving conditions. Circulating coolant throughout the engine absorbs excess heat, which is then expelled when the coolant flows through the radiator.

When the engine is cold, the thermostat (which is nothing more than a temperature-sensitive valve) is closed, preventing coolant flow through the radiator. Once the engine reaches operating temperature, the thermostat opens, allowing coolant to flow through the radiator and the entire cooling system. Figure 1 shows a typical coolant circulation pattern.

The coolant is circulated through the system by means of a water pump. The water pump is driven by an accessory belt or chain driven by the engine. For example, in the old 2.4L 4-cylinder engines used in vehicles such as the PT Cruiser, the timing belt also drives the water pump.


Because of the important role the cooling system plays in the overall performance of the vehicle, maintenance of this system is required and necessary. The first thing to start with is the coolant. Lack of proper maintenance leads to problems. Here’s some coolant basics to ensure there are no problems.

FCA US LLC offers three different coolants. The oldest of the three is the 3-year/50,000-mile coolant. The second coolant is the 5-year/100,000-mile coolant, which debuted in 2012. The third, and newest, coolant is the 10-year/150,000-mile type.

One of the features of this new coolant, which is now used on all vehicles built from 2013 to the present, is its concentration. It can be purchased prediluted, or non-diluted, which is the traditional way coolant is sold. The prediluted version, P/N 68163849AB, is a 50/50 blend of coolant and water (this is the recommended mixture of coolant and water). Do not add water to this blend. It can be poured into the overflow reservoir or radiator straight from the bottle. The non-diluted blend is P/N 68163848AB.

It is important to note that these three coolants are non-compatible with one another. Do not mix these coolants together in any concentration. If, for some reason, one of these coolants is mixed with another already in the cooling system, serious problems will occur. The coolant will coagulate, preventing the flow of coolant. This can lead to engine overheating.

Another interesting fact about these coolants is that each coolant can be used in any model year FCA US engine. For example, the 3-year coolant can be used in a 2017 Pacifica and the newest 10-year coolant can be used in a 2002 PT Cruiser. If the coolant is being changed in a particular engine, the previous coolant must be thoroughly flushed out.


Coolant should be changed and flushed at the recommended service interval. The procedure is straightforward. When the engine has cooled, remove the radiator cap. Open the drain valve at the bottom of the radiator. (Remember, the engine block and heater core represent about half of the cooling system capacity.)

To help remove sediment from the system, flush it with water until the discharge runs clear. If the discharge is rusty, use Mopar® Cooling System Flush P/N 04856977AC. Close the drain valve and fill with clean water and cooling system flush/cleaner. Set the heater on high. Start the engine and run it until the heater activates. Stop the engine, let it cool, then drain the radiator again.

Fill the cooling system with the desired coolant. If in doubt, check the owner’s manual for the specified antifreeze usage. If using prediluted coolant, do not add any water. If using concentrated coolant, add a 50/50 mixture of coolant and water. Set the heater on high.

Start the engine and run it until the heater activates. When the engine cools, top off the radiator and fill reservoir with prediluted coolant, or a 50/50 mixture, depending on the coolant used. Check the fluid level periodically.


Because most systems on the modern automobile are computer-controlled, diagnosing problems often requires the use of a scan tool. The cooling system is a bit different. The most common problems are easily detected. For instance, leaks can be seen on the ground under the car. Also, the temperature gauge might indicate the engine temperature is above normal (the needle or indicator has usually moved into the orange-colored zone on the gauge or scale).

The most common source of a coolant leak is a bad water pump. Leaks can also occur at hose connections, or split or ruptured cooling hoses. When this occurs, a visual check of the cooling system often uncovers the source of the leak. If the heater core corrodes and starts to leak, the leak will be seen inside the passenger compartment.

Coolant leaks can also be internal. This occurs if the head gasket fails. Coolant will leak into one or more cylinders. Steam in the exhaust stream is one sign of a blown head gasket. Another is the presence of coolant in the engine oil.


The most noticeable change in the cooling system since the dawn of the environmental age (early 1970s) is the electrical cooling fan. Prior to that time, cooling fans were run directly off the engine. The fan operation is now controlled by a solid state relay. The relay provides voltage to the fan motors that is proportional to the pulse width received from the powertrain control module (PCM). The duty cycle ranges from 30% (low speed operation) to 100% (high speed operation). This allows infinitely variable fan speeds for reduced fan noise, A/C performance and better engine cooling.

It should be noted that the electronics that control the cooling fans do not, as a general rule, fail; however, the fan motors can. The usual culprit is the motor bearing. When this occurs, under most circumstances, the Check Engine light will not illuminate. As long as the relay receives the pulse width from the PCM, the PCM assumes the fan motors are operating. So, if coolant temperature is rising, but the coolant level is good, check the fan operation.



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