Lesson 5/Learning Event 2
The cooling system should never be allowed to stay for an extended time without the protection of a rust
inhibitor. This is particularly true just after cleaning as considerable corrosion may take place in a few hours.
Use an antifreeze hydrometer to check the amount of protection given by the antifreeze.
After cleaning and flushing a cooling system and the temperature is expected to stay above 32F, add
amount of inhibitor that is recommended on the inhibitor container or in the technical manual. Start
engine and operate it until operating temperature is reached. This is to open the thermostat valve so
inhibitor will circulate through the entire system. If antifreeze is to be added to the system, do not add
When the temperature is expected to go below 32F or if the vehicle is to be maintained combat ready,
antifreeze is used. If temperatures are expected to go lower than -55F, completely drain the cooling system
and refill it with arctic-type antifreeze.
If the freezing temperatures are expected to remain above -55F, fill the cooling system with a mixture of water
and ethylene glycol antifreeze. Prepare the mixture according to the protection tables given on the antifreeze
containers. Always tie a tag on the radiator, telling how long it is protected.
When you are asked to locate trouble in a cooling system, it will probably be because one or more of the
following complaints: the engine overheats, coolant is being lost, or the engine fails to reach operating
temperature. Because of the differences in the design of different vehicles, the causes for these complaints may
vary. For this reason, you should always refer to the troubleshooting section of the technical manual for the
vehicle you are working on.