Yanmar 3HM - Page 174

168
Thi s technique can beu sed to che ck thermostat openin g
by
marking the th cnno stat housing with two thermomelt
sticks: one with a temperature lower than the thermostat
opening temperature, and
one with a temperature higher
than the full open position. When the coolant or water
reaches the first temperature, the mark made by that stick
will melt. The mark made by the second stick will not melt
until the coo lant or water increases to that temperature.
WARNING
Do not remove the pressure jill cap from a
fresh ..... ater(closed) coolingsystem while the
engineis
warm. Coolant may blowout ofthe
heat exchanger and cause serious personal
injury.
Overheated Engine
1. Relieve the freshwater cooling system pressure by
carefully removing the pressure fill cap from the heat
exchanger. Sec Figure 15. typical.
2. Rub a 180
0
F (82
0
C) the rmo melt stick on the th ermo -
stat cove r.
3. Start the engine and run at a fast idle.
4. Ifn o coo lant flows into the heat exchanger by the time
the mark starts to melt. either the
thermostat is stuck
closed or the water pump is failing. Remove the thermo-
stat and test it as described in this chapter.I ft he results are
satisfactory, replace the water pump.
Slow Engtne Warm -Up
I. Relieve the freshwater cooling system pressure by
carefully removin g the pressure
fill cap from the heat
exchanger. Sec
Ftgure IS, typical.
2. Rub the 160
0
F (71
0
C) thermomelt stick on the ther-
mostat cover.
3. Start the engine and run at a fast idle.
4. If coolant or water flows into the heat exchanger be-
fore the mark starts to melt. the
thermostat is stuck open
and should
bereplaced.
IIUSE
REPLACEMENT
Replace any hoses that are cracked, brittle, or very soft
and spongy. Ifa hose is in doubtfulcondition, replace
it to
be on the safe side. Hoses in some installations are ex-
tremely difficult to change; attention to hose condition
can prevent a failure while off-shore.
Hose manufacturers generally rate coo ling system hose
life at two years. How long the
hoses will last depends a
great deal on how much the boat is used and how well the
CHAPTER EIGHT
system is maintained; however, it is a good idea to change
all hoses every two years. Always replace a cooling sys-
tem
hose with the same type as removed. Pleated rubber
hoses do not have the same strength as reinforced molded
hoses. Check the hose clamp condition and install new
marine-grade clamps with a new hose, if necessary.
Partially drain the cooling system when replac ing upper
hoses. Completely drain
it when replac ing lower hoses.
I. Loosen the clamp at each end of the hose to be re-
moved. Grasp the hose and twist it
off the fitting with a
pulling motion.
2. If the hose is corroded 10 the fitting and will not twist
free, remove the clamp and insert a small screwdriver or
pick tool between the hose and
the fitting. Work the tool
around
the fitting, then remove the hose.
3. Clean any rus t or corrosion from the fining with a wire
brush.
4. Wipe the inside diameter
of the new hose with liquid
detergent and install the hose ends on the fittings with a
twisting motion.
5. Position the new clamps a
tleas t 1/4 in. (6.4 mm) from
the end
of the hose. Make sure to position the clamp screw
for easy access with a screwdriver or nut driver. Tighten
each clamp snugly.