Insufficient Water Flow From Alpha One Stern Drive Unit Seawater Pickup Pump - MerCruiser GM4 Service Manual

Insufficient Water Flow from Alpha One Stern
Drive Unit Seawater Pickup Pump
1 Seawater shutoff valve partially or fully closed
(if equipped)
2. Water pick up clogged with foreign material
3. Kinked or broken bell housing to gimbal housing
water tube hose
4. Corroded through gimbal housing water tube
5. Water pick up inserts warped. (Engine will over
heat while boat is underway.)
6. Damaged gear housing or accessories improperly
installed on boat bottom or transom (speedometer
pick up, depth sounder transducer, etc) Substan
tial amount of barnacles or other marine growth
on gear housing or boat bottom. (Engine will over
heat while underway only)
7. Stern drive installed too high on transom or drive
unit trimmed out too far out allowing air to be
drawn into pump. (Engine will overheat while un
derway only)
8. Bell housing -to-driveshaft housing O-ring missing
or damaged
9. Faulty seawater pick up pump
10. Seawater pick up tube corroded thru
11. Driveshaft housing water pocket cover cracked
12. Broken-off impeller blade or other obstruction in
water passages (usually lodges in driveshaft
housing water pocket cover or cross drilled water
passage).
13. Water passage in driveshaft housing improperly
drilled
Index
1C- 36 - TROUBLESHOOTING
CAUSE SPECIAL INFORMATION
5. Pick up must not protrude above gear housing
surface or inserts will create an irregular or
turbulent water flow over the water pick up holes.
Consequently, this may cause loss of cooling
water and subsequent engine overheating. This
condition can be identified by cavitation burn
(pitting or erosion) the gear housing in the area
aft of the water pick up.
6. An object or an irregularity on boat or gear hous
ing in area close to to water pick ups could create
turbulence in water flow going to water pickups.
This could aerate the water flow and cause en
gine to overheat
7. Contact boat company if stern drive is too high.
Instruct operator on proper trimming technique if
until is trimmed out too far.
12. To check cross drilled water passages in drive
shaft housing, remove plug and pipe plug located
under decal on starboard side of housing. Drive
unit must be shifted into reverse to remove pipe
plug.
90-816462 2-695