Hot Enough For Ya?

It may be the dead of winter, but cooling system problems know no season. Here are some tips for proper cooling system diagnostics.

Cooling system maintenance is critical to the overall operation and efficiency of the engine in any vehicle. And while you might not think that cooling system problems can occur during the cold weather months, nothing is farther from the truth. Cooling system problems know no season and can occur any time of the year during any type of weather.

Let’s take a closer look at cooling system problems along with system testing and diagnostic procedures. We’ll look a number of topics including, but not limited to, leak tests, flow checks, thermostat problems and coolant concentration.

Cooling System Basics

The primary purpose of an engine cooling system is to maintain engine temperature in a range that will provide satisfactory engine performance and emission levels under all expected driving conditions. It also provides hot water (coolant) for the passenger compartment heater and cooling for the automatic transmission. All of this is done by transferring heat from engine metal to coolant, moving this coolant to the radiator and then transferring this heat to the ambient air.

In order for the cooling system to operate efficiently, the correct volume of coolant at the proper concentration must be maintained in the system. While plain water would work in a cooling system, a number of problems would soon materialize. First of all, water has a lower boiling point than coolant, and a higher freezing point than coolant, it can cause corrosion within the system, and it does not have any lubricating properties. As a result, specially formulated coolants have been developed over the years to maximize the performance of the cooling system.

Cooling System Problems

How do you know if a cooling system problem exists? Usually, the first sign is an elevated coolant temperature. Most vehicles have a coolant gauge on the instrument panel (IP) with an area of red that would indicate overheating if the needle moves into that area. If there is no gauge in the vehicle, a red warning lamp will illuminate.

Tell-tale signs of orange or green drops of coolant on the garage floor indicate a problem. If left unattended, enough coolant can leak out to cause an overheating problem. Also, a leak might indicate a bad water pump, which should be replaced as soon as it is detected. A bad water pump will not properly circulate coolant, leading to an overheating problem.

When a problem is suspected with the cooling system, a series of tests can be run to pinpoint the problem. Let’s review several of these tests, beginning with the cooling system leak test.

Cooling System Leak Test

It stands to reason that leaks anywhere in the cooling system mean trouble. Leaks decrease the volume of coolant, reducing the efficiency of the system. Leaks can occur at a multitude of locations. The best way to pinpoint the source of a leak is to pressure test the system.

Remove the radiator pressure cap (be sure the engine is not hot) and wipe the radiator filler neck seat to be sure it is clean. Check to make sure the radiator is full. Attach a radiator cooling system tester, as shown in Figure 1.

Apply 15 psi of pressure. If the pressure drops more than 2 psi in two minutes, inspect all points for external leaks. Coolant is usually green or orange in color, so detecting a leak should not be that difficult. The radiator and all hoses should be shaken at 15 psi pressure to simulate engine vibration. Some leaks only occur when the vehicle is moving.

Many times a bad water pump will leak through the weep hole. Locate the water pump (it might be difficult on some front-wheel-drive vehicles) and see if a trail of coolant begins at that point. If that is the case, the water pump is bad.

If there are no external leaks with the drop in pressure, remove the tester and start the engine. Run the engine to operating speed in order to open the thermostat. Reattach the tester. If the needle fluctuates, that usually indicates a combustion leak (most likely a head gasket). Often times an internal leak from a blown head gasket or cracked engine block can be verified by steam being emitted from the tailpipe.

Cooling System Flow Check

To determine whether the coolant is flowing through the cooling system, perform one of these two tests. The preferred test requires removal of the pressure cap when the engine is cold.

Remove a small amount of coolant. Start the engine and let it idle until the thermostat opens. You should observe coolant flow while looking down the filler neck. After you detect flow, install the pressure cap.

The second method is simpler. Start the cold engine and let it idle until normal operating temperature is reached. Feel the upper radiator hose. If it is hot, the coolant is circulating.

If either test indicates that the coolant is not flowing, there is some type of obstruction in the system. Many times it is the thermostat (we’ll review testing that component) or some type of blockage in the radiator core.

Coolant Concentration Testing

Engine coolant, mixed in the correct proportions with distilled water, is the lifeblood of the cooling system. Coolant concentration should be checked when additional coolant is added, or the system is flushed and refilled. A coolant mixture with a freeze point of -34° F to -50° F provides optimum engine cooling and corrosion protection.

The most common test for coolant concentration is the specific gravity test. This test is done using a hydrometer, which measures the amount of glycol in the mixture. This instrument looks like a large meat baster with several balls in the tube. Insert the end of the instrument into the coolant recovery tank, squeeze the bulb and draw out some coolant. The number of balls floating in the mixture is proportional to the level of freeze protection (freeze protection increases with the number of balls floating).

Pressure Cap Testing

The cooling system is equipped with a pressure cap that releases excessive pressure, maintaining pressure in the range of 14 to 18 psi. This cap allows the system to operate at a pressure greater than atmospheric, raising the boiling point of the coolant and the capacity of the system. Testing the cap is simple.

Dip the pressure cap in water. Clean any deposits off the vent valve or its seat. Attach the cap to the end of the Pressure Cap Test Adaptor (see Figure 2). Working the plunger, bring the pressure to 15 psi on the gauge. If the pressure cap fails to hold a minimum pressure of 14 psi, replace the cap. If the pressure cap tests properly, but will not hold pressure or vacuum when installed on the filler neck, inspect the filler neck and the cap top gasket for irregularities. These irregularities can prevent the cap from sealing properly.

The neck can easily be tested with the radiator pressure tool. Remove the overflow hose at the radiator filler neck nipple (see Figure 3). Attach the pressure tool to the filler neck nipple and pump air into the radiator. The pressure cap upper gasket should relieve pressure at 10-18 psi and hold pressure at 8 psi minimum.

Thermostat Testing

The thermostat is operated by a wax filled chamber (pellet) which is sealed. When the heated coolant reaches a predetermined temperature, the wax pellet expands to overcome the closing spring and water pump pressure. The valve opens and coolant flows into the engine block.

Thermostat diagnostics are included in the on-board diagnostics programming of the PCM. The malfunction indicator light (MIL) will illuminate and a diagnostic trouble code (DTC) will be set when an open too soon condition occurs. Do not change a thermostat for poor heater performance or temperature gauge position unless a thermostat irrationality code is present.

The thermostat failing to shut is the normal and usual long term mode of failure. Also, this condition usually occurs on high mileage vehicles. When the thermostat fails to close, the temperature gauge on the (IP) will indicate this condition.