COOLING
Page 4B-10 90-855347R1 JANUARY 1999
Problem Diagnosis
Condition Recommended Range Possible Cause
Pressure below specification @
idle
1.0 – 3.0 PSI (6.8 – 20.5 kPa) •Poppet valve spring defective
(weak, broken, missing)
•Defective poppet valve seal
•Thermostat stuck open
•Severe internal leak
•Low output water pump
•Inlet restriction
•Strainer screen for air compres-
sor water supply is restricted
Pressure above 5 psi (34.2kPa)
@ idle
1.0 – 3.0 PSI (6.8 – 20.5 kPa) •Plugged poppet by-pass pas-
sage or fuel cooler
Pressure does not drop between
1000 – 2500 RPM indicating pop-
pet valve has opened
4 – 9 PSI (27.4 – 61.6 kPa) be-
tween 1000 – 2200 RPM
•Wrong poppet valve spring
•Low output water pump
•Inlet restriction
•Poppet valve vent hole plugged
or restricted
•Severe internal leak
•Defective poppet valve seal
Poppet valve flutter/water pres-
sure drop does not stabilize prior
to 2500 RPM
4 – 9 PSI (27.4 – 61.6 kPa) be-
tween 1000 – 2200 RPM
•Wrong poppet valve spring
•Low output water pump
•Inlet restriction
•Broken diaphragm in poppet
valve
•Severe internal leak
•Defective poppet valve seal
Pressure is below minimum spec-
ification @ W.O.T.
12 PSI (54.9 – 68.5kPa) •Inlet restriction
•Engine mounted too high on
transom
•Engine trimmed out too far
•Configuration of boat bottom in-
terfering with adequate flow of
water to coolant inlets
•Severe internal leak
•Low output water pump
•Plugged strainer screen for air
compressor water supply
Pressure higher than normal @
W.O.T., but engine still indicates
overheat condition
Maximum pressure – 23 PSI
(157.4 kPa)
•Outlet water passages restricted.
•Steam pocket has formed at top
of powerhead due to lack of cool-
ing water
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