Mercury 225 EFI, Service Manual

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COOLING
Page 4B-12 90-884294 OCTOBER 2001
Problem Diagnosis
Condition Recommended Range Possible Cause
Pressure below specification @
idle 1.5 – 4.5 PSI (10.3 – 30.8 kPa)
•
Poppet valve spring defective
(weak, broken, missing)
•
Defective poppet valve seal
•
Thermostat stuck open
•
Severe internal leak
•
Low output water pump
•
Inlet restriction
Pressure above 5 psi (34.2kPa)
@ idle 1.5 – 4.5 PSI (10.3 – 30.8 kPa)
•
Plugged poppet by-pass pas-
sage or tell-tale
Pressure does not drop between
1000 – 2500 RPM indicating pop-
pet valve has opened 6 – 7 PSI (41.1 – 47.9 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
•
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. 8 PSI (54.8 kPa)
•
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
Pressure higher than normal @
W.O.T., but engine still indicates
overheat condition Maximum pressure – 30 PSI
(206.8 kPa)
•
Outlet water passages restricted.
•
Steam pocket has formed at top
of powerhead due to lack of cool-
ing water