1100 SERIES DIESEL TRUCK ENGINE Cooling System Caterpillar

Cooling System
1.1. Testing Cooling System Pressure

A pressurized cooling system serves two purposes. First, it permits safe operation at coolant temperatures higher than the normal boiling point; thereby, providing a margin of cooling for those intermittent peak loads. Secondly, it prevents cavitation in the water pump and reduces the possibility of air or steam pockets forming in the coolant passages.

Many times engine overheating is caused by failure to make simple systematic inspections. Visual inspections should be made before testing.

Coolant Level: Check the engine coolant level with engine stopped and cool. Always release cooling system pressure before checking. Fill to the proper level with water, as free as possible from scale forming minerals, not softened water. During freezing weather add sufficient permanent type antifreeze to the coolant to prevent freezing. Make up water added without the proper proportions of inhibitor can cause excessive mineral deposits. (Use inhibitor as recommended on container.)

Most commercial antifreeze solutions contain rust inhibitors, however, it is recommended the adding of AVSpare Coolant System Inhibitor to glycol base antifreeze if protection is for temperatures above -20°F (-29°C). If protection is for temperatures -20°F (-29°C) or below, do not add inhibitor.

------ WARNING! ------

Inhibitor contains alkali. Avoid contact with eyes. Avoid prolonged or repeated contact with skin.



Add coolant slowly to a hot engine (engine running) to prevent possible cracking or distorting the cylinder heads.

If a loss of coolant is noticeable, check for leaks in the system. After filling the system, start the engine and add coolant as necessary to maintain a full system during engine warm up. Running the engine at operating temperature will permit the temperature regulator to open and allow the coolant to circulate and purge air from the entire system. Some systems will normally loose some coolant during initial warm up cycle.

Cleaning the Radiator (External): Clean dirt and trash from between the tubes of the radiator. Accumulation of debris may cause excessively high operating temperature. Wash, brush or blow the dirt out with whichever method is available and most effective. When cleaning with air do not exceed 30 PSI (2 kg/cm2).

Cleaning the Cooling System (Internal): Clean the cooling system periodically. Mineral deposits can cause serious engine damage by retarding the transfer of heat to the coolant. A deposit of lime 1/32 inch thick insulates the same amount as 2 inches of steel, reducing the heat transfer substantially. Loose scale and sediment deposited in the cooling system will reduce circulation, resulting in possible engine damage. To clean, stop the engine when it is at normal operating temperature and drain as quickly as possible. Flush thoroughly, then fill with a solution of 3.2 ounces of Oxalic Acid or Sodium Bisulfate per one gallon of water. Run the engine at operating temperature one-half to one hour, then drain and flush until water is clear. Fill with a solution of .8 of an ounce of Sal Soda per one gallon of water and run the engine ten minutes. Drain, flush and fill with water, adding corrosion inhibitor or the desired amount of antifreeze.


Filling the Cooling System: When filling a cooling system it is essential for the system to be filled completely and air pockets eliminated. Air trapped in the system can cause loss of water pump prime resulting in coolant flow stoppage and possible engine damage.

Proper filling procedure is necessary to assure the cooling system is completely filled. Follow the step-by-step recommended procedure.

1. Fill the radiator with water containing corrosion inhibitor and/or antifreeze solution.
2. Start the engine and run at low idle.
3. Add coolant as necessary to keep level visible in top tank.
4. Run engine until there is warm coolant in the top tank.
5. Check coolant after a short period under load.

Testing the Temperature Gauge: Remember that boiling point temperature and pressure go hand-in-hand and neither one can be tested logically without considering the other. For example, the effect of pressure and altitude upon the boiling point of water is shown in the chart.

If overheating and loss of coolant is a problem, a pressure loss in the system could be the cause. If an overheating condition is indicated on the temperature gauge and loss of coolant is not evident, check the accuracy of the temperature gauge. Make this check by installing a reliable thermometer with a suitable bushing in the top plug opening of the front cover.


Use CAUTION when working around moving parts with the engine running.

Start the engine. Partially cover the radiator to reduce air flow and cooling. The reading on the instrument panel gauge should agree with the reading on the thermometer.

Testing Cooling System Pressure

In a pressurized system, a leaking radiator cap allows loss of pressure and coolant. For a simple check of cooling system pressure, install a pressure gauge in the radiator filler neck and pressurize the system. Do this by either using an air valve and a hand pump, or by operating the machine until the coolant reaches operating temperature. System pressure should rise to 7 ± 3 psi, and any additional pressure should force air past the relief valve through the overflow opening. Do not allow pressure to exceed 10 psi. The system must hold a minimum pressure of 7 psi, and pressure must remain constant with the air supply shut off or the engine running at a constant temperature.

NOTE: These cooling system pressures will vary depending on installation. Refer to the vehicle manufacturer's Operation and Maintenance Guide for additional information.


If the pressure isn't maintained, overflow loss can occur as cooling system temperature rises. If the system does not hold pressure, find the leak. Carefully inspect the radiator cap, seals, sealing surfaces and the top tank filler neck surface for damage.


Thermostats: Check thermostats yearly and install new ones if necessary. Thermostats are stamped with the opening temperature: Either 165°F (74°C) or 175°F (79°C) thermostats are used. This is the approximate temperature at which thermostat starts to open. A thermostat is fully open at approximately 20F° (11C°) above the opening temperature.


1. Remove the thermostat from the housing.
2. Submerge the thermostat and a thermometer in a pan of water as shown.
3. Apply heat to the pan slowly and stir the water to maintain uniformity.
4. Observe the opening temperature of the thermostat.

If the thermostat does not operate correctly, install new thermostats. These engines should never be operated with the thermostats removed.

Water Hoses: Inspect all water hoses and install new hoses if they show signs of cracking or leaking. Install new hoses at least once a year.

Air, Gases and Steam in the System: Incomplete or improper filling is a major cause of air in the cooling system.

Air in the system produces foaming or aeration and will prevent the water pump from delivering full circulation of coolant to all parts of the engine.

Exhaust gas leakage into the cooling system causes similar conditions. Exhaust gas can enter through internal cracks, damaged cylinder heads, or gaskets.

Air being added to the cooling system while it is running is one cause of overheating which can be located by a simple test known as the "bottle test". The equipment required to perform such a test consists of a 1 pint bottle, a bucket of water, and a length of hose with an inside diameter large enough to fit over the end of the radiator overflow pipe.

TO TEST: Fill the cooling system to proper level. Wire open the relief valve in the radiator cap. Install the radiator cap and tighten. Assemble the rubber hose over the end of the overflow pipe.

Start the engine and operate it at high idle speed for at least five minutes after the engine reaches operating temperature. Block off part of the air flow through the radiator to maintain operating temperature. After the temperature has stabilized and all expansion air has vented out, place the loose end of the hose in the water filled bottle which is inverted in the bucket of water. If it takes less than 40 seconds to displace the water in the pint bottle, with engine at high idle, leakage into the cooling system is excessive.