August 26, 1960
Bulletin No. SB-796
Trouble shooting
SUBJECT: OVERHEATING - CYLINDER HEAD GASKET REPLACEMENT, ALL MODELS.
Whenever problems of overheating are encountered on any engine, the normal recommended
procedure is to check out the following possible causes:
1. An inoperative water pump due to worn or faulty pump parts such as,
(a) impellers, (b) housings, (c) pump plates, (d) grommets, (e) seals, etc.
2. Clogged or obstructed water passages, hoses, intake screens, etc. due to
a. Corrosion - particularly in salt water areas.
b. Metal flashing, a thin film of metal, left in as a result of
die casting.
c. Other foreign matter or objects.
3. Clogged water jackets and passages in cylinder blocks and heads.
Look for the same causes as listed under 2 a, b and c preceding.
4. Inoperative thermostats, vernatherms or water pressure valves on
all engines equipped with thermostatically controlled cooling systems.
5. Faulty gaskets and water hose connections.
6. Replace all affected cooling system gaskets - INCLUDING CYLINDER
HEAD GASKETS.
Step #6 is strongly recommended because overheating tends to dry out the gaskets and
causes them to shrink. This is especially true of the cylinder head gasket. It's
basic function is to provide a tight seal between head and block to confine water to
its respective passages, and seal combustion pressures inside the combustion chamber.
Since combustion pressures are very high, the head gasket may no longer efficiently
perform its intended function and consequently allow exhaust gases to enter the cooling
system, thus intensifying the heating problem.
Always replace cylinder head gaskets on any engines which have overheated. Do this
after having first checked all other possible causes, or after being certain the cause
of overheating has definitely been corrected. Otherwise, the new head gasket may also
dry, shrink and again allow exhaust gases to enter the cooling system.
Repeat, as your final corrective operation, ALWAYS replace cylinder head gaskets on
all engines which have overheated.
JOHNSON MOTORS
W. W. DeWees
W. W. DeWees
Service Department
WWD:eb
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