Special Instructions

tive.) Maintaining coolant level at all times cannot be over

d. Problems with engine cooling fans, drive belts (or

emphasized.

drive shafts if applicable) and pulleys have contributed to

overheating problems. Inspection and maintenance of

these items should include the following:

WARNING

(1) Some early 6V53T engines and M551 ARAAV

cooling fans were equipped with aluminum pulleys. Early

Remove radiator cap(s) slowly to relieve pressure

failures resulted in a change to cast iron pulleys. Only cast

and avoid injury to personnel.

iron pulleys are authorized for use on all cooling systems

for 6V53, 6V5,3T and 8V71T engines.

b. During initial radiator fill, or refill after cooling

(2) Be sure pulleys are tight and properly alined.

system has been disturbed in any way to affect coolant

Burrs, nicks and other sharp edges can cause early belt

level, it is important that coolant be added slowly,

failure and should be removed or pulleys replaced.

particularly the last few quarts. This is necessary to permit

(3) Fan shafts should be examined for spline or

trapped air to escape and assure that maximum amount of

bearing wear.

coolant has been added to the system. The radiator

(4) Belts must be properly adjusted for effective

should be filled to the top of filler neck When filling or

operation. Belts that are too loose will slip and belts

refilling cooling system remove the radiator cap (if system

adjusted too tight will wear prematurely as well as impose

has two caps both must be removed) and proceed as

undue strain on bearings, shafts and pulleys.

follows:

(1) Add coolant slowly until radiator is completely

filled (never add cold coolant to a hot engine). Excess

NOTE

coolant, if any, will be automatically expelled through the

Where belts are installed in multiples (two or more)

pressure relief Replace cap(s).

they must be replaced in sets because they are

(2) Run engine for about 5 minutes, or if possible

matched sets. Replacing one belt in a set will

until normal operating temperature is reached.

result in belt failure since the tighter new belt will

(3) Stop engine and recheck coolant level. Add

be doing all the work. Refer to the applicable

coolant as required to bring level to top of filler neck and

technical manual for correct tension and

reinstall cap(s).

adjustment procedure.

c. Defective or improper radiator caps (or pressure

relief valve when applicable) can cause a loss of pressure

(5) Cooling fan blades must be free of bends, nicks,

or abnormally high pressure. Each cooling system is

or breaks These fans are precision balanced at time of

designed so that the engine will operate at a temperature

manufacture This balance can be affected by tears, bends

that is expected to give the best performance PSI (pounds

and/or missing chunks which lead to early failure, possible

per square inch) rating of the cap (or relief valve)

damage to surrounding parts and injury to personnel.

determines the temperature at which coolant will boll. If

(6) Observe fans, shafts, pulleys and belts in

cap or relief valve has a lower PSI rating (defective or

operation to be sure all items function properly.

improper) than system requires, coolant will boil at a lower

e. Properly functioning thermostats are essential to

temperature causing loss of coolant, which if not

efficient operation of cooling systems.

Defective

corrected, will result in overheating If cap (or relief valve)

thermostats should be replaced but under no

has a rating too high, the boiling point is raised and more

circumstances should engines be operating without

pressure is imposed on the cooling system than it was

thermostats. Assure that correct thermostat is installed In

designed for. This may cause leaks in hoses, connections

the proper place.

or radiators. The following points pertinent to radiator

Clogged radiator cores restrict engine cooling.

caps are provided for consideration.

Every effort should be made to keep radiators as clean as

(1) During normal operation, if coolant tends to stay

possible In some areas dust having a high clay content

above 200F, radiator cap may be faulty.

tends to adhere to the radiator core, frequent cleaning is

essential to preclude overheating. Radiator maintenance

(2) If pressure relief continues to expel coolant below

should include.

normal operating temperature level, radiator cap may be

(1) Remove dirt and other foreign matter from

faulty.

radiator air passages. Use compressed air or stream of

(3) On vehicles having radiator caps exposed and

water to dislodge imbedded material, do not use steam.

subject to damage by crew members stepping on them it

When practical, direct air or water from direction opposite

is recommended that a "NO STEP" caution be stenciled

normal intake flow. A radiator and oil cooler cleaning tool

on the deck near the radiator cap location.

is available for effective cleaning(10, fig 2-1).

(4) Pressure rating of the radiator cap is stamped on

top surface of cap Assure that cap is the one prescribed

by applicable technical manual.

2-18