Yanmar 1GM User Manual page 41

TROUBLESHOOTING
1. Loose pump drive belt (except IGM models)-A loose
drive belt prevents the circulating pump from operating at
the proper speed.
2. Loose hose or pipe connections-Air may be drawn
into the suction side of the system.
3. Worn or defective water pump-A worn or defective
pump may not provide sufficient cooling water.
4. Dirty cooling system-Debris in the cooling system
prevents adequate heat transfer to the cooling water.
5. Defective or incorrect thermostat-A defective ther-
mostat may stay closed or not open sufficiently to allow
hot water to leave the engine. An incorrect thermostat
may open at a temperature higher than specified, thereby
raising the temperature of the cooling water in the engine.
Conversely, a thermostat that stays open and doesn't close
or opens at a low temperature will cause the engine to run
at less than optimum temperature.
ENGINE EXHAUST SMOKE
The engine should emit colorless exhaust smoke or
smoke that appears no more than a light haze. If the ex-
haust smoke is black, white or blue, an engine problem
exists.
Blue Smoke
Blue exhaust smoke indicates that oil is burning during
the combustion process. Look for a condition that allows
oil to enter the combustion chamber, such as a broken pis-
ton, broken or stuck piston rings, a damaged cylinder
wall, worn valves or guides, a defective crankcase vent, or
an overfilled oil sump.
White Smoke
Unburned fuel causes white exhaust smoke. The un-
burned fuel may be due to retarded fuel injection timing or
insufficient compression pressure. Low compression
pressure may be caused by a damaged cylinder gasket,
broken piston rings, leaking valves or incorrectly adjusted
valves. Raw, unburned fuel may be due to incorrect fuel
(low cetane rating) or a defective injector.
NOTE
White smoke may also be due to coolant
leaking into the combustion chamber.
35
Black Smoke
Black exhaust smoke results from excess fuel (rich) that
forms soot when burned. Either excess fuel or insufficient
air can cause black smoke. Some possible causes are a de-
fective fuel injection pump, poor injector spray pattern,
low injection opening pressure, clogged air intake, re-
stricted exhaust system or low compression pressure.
ENGINE NOISES
Often the first evidence of an internal engine problem is
a strange noise. That knocking, clicking or tapping sound
never heard before may be warning of impending trouble.
While engine noises can indicate problems, they are
difficult to interpret correctly; inexperienced mechanics
can be seriously misled by them.
Remember that diesels are much noisier than gasoline
engines and have a normal clatter at idle, especially when
cold. It is necessary to become accustomed to these nor-
mal noises in order to detect possible problem-associated
noises.
Professional mechanics often use a special stethoscope
for isolating engine noises. The home mechanic can do
nearly as well with a sounding stick, which can be an ordi-
nary piece of dowel, a length ofbroom handle or a section
of small hose. Place one end in contact with the area in
question and the other end near the ear to hear sounds em-
anating from that area. There are many strange sounds
coming from even a normal engine. If possible, have an
experienced mechanic help sort out the noises.
Clicking or Tapping Noises
Clicking or tapping noises usually come from the valve
train and indicate excessive valve clearance. A sticking
valve may also sound like a valve with excessive clear-
ance. In addition, excessive wear in valve train compo-
nents can cause similar engine noises.
Knocking Noises
A heavy, dull knocking is usually caused by a worn
main bearing. The noise is loudest when the engine is
working hard, such as accelerating at low speed. It is pos-
sible to isolate the trouble to a single bearing by disabling
the fuel injectors on multicylinder engines one at a time.
By disabling the fuel injector nearest the bearing, the
knock will be reduced or disappear.
Worn connecting rod bearings may also produced a
knock, but the sound is usually more metallic. As with a