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DRIVES WITH IMPELLER IN BELT DRIVEN PUMP

TO TROUBLE SHOOT THE WATER SYSTEM OF A MERCRUISER YOU

MUST DEVIDE THE COOLING SYSTEM INTO PARTS AND CHECK EACH

FOR PROBLEMS.

1) THE DRIVE AND INPUT HOSES

THE EASIEST CHECK FOR THE DRIVE AND PUMP SECTION IS TO DISCONNECT THE HOSE WHICH

COMES FROM THE DRIVE BEFORE IT PASSES THRU ANY OIL COOLERS OR PUMP..  WITH A FLUSHETTE ON

THE DRIVE.

(MAKE SURE THAT THE WATER SEAL ON THE FLUSHETTE ON THE SIDE OPPOSITE THE HOSE

HAS EXCESSIVE WATER LEAKING AROUND THE SEAL WHICH MEANS THE FIXTURE IS ON CORRECTLY.)

WITH THE ENGINE OFF.

THE WATER SHOULD FLOW FREELY FROM THE HOSE FROM TRANSOM PLATE ADAPTER AND

SEA WATER PUMP, WHICH IS DISCONNECTED FROM THE PUMP AND HANGING IN THE BILGE.

CHECKING FURTHER WITH THE CITY HOSE CONNECTED TO THE PUMP  END SHOULD FLOW FREELY AND GUSH

OUT OF THE OUTDRIVE SCREENS ON EACH SIDE OF THE DRIVE.  IN OTHER WORDS FREE FLOW FROM THE INPUT

SCREENS TO THE RAW WATER PUMP INPUT.  IF PRESSURE DEVELOPS UPON THE REVERSE TEST YOU SHOULD

SUSPECT BRAVOITIS COVERED BELOW.

2) THE INTERNAL ( PUMP THRU T/STAT) HOSES

WETTING ALTERNATOR ETC,) INSERT THE CITY WATER HOSE IN THE OUTPUT HOSE REMOVED FROM THE

RUBBER IMPELLER PUMP HEADING INTO THE COOLERS ETC AND CLAMP.  FULL FLOW FROM THE CITY

HOSE SHOULD MAKE NO  PRESSURE BY THE CLAMP AND FULL FLOW SHOULD COME FROM THE END

FOR THE T/STAT HOUSING.  PRESSURE WOULD INDICATE A CLOGGED OIL COOLERS OR A FLAP IN ONE

OF THE HOSES CAUSING BLOCKAGE.

3) THE MANIFOLD AND ELBOWS

THE INPUT HOSE FOR EACH MANIFOLD IS FED BY ABOUT 1-1/8" HOSE THEN IT FLOWS INTO THE ELBOW

AND OUT INTO THE EXHAUST.  EVERY DROP OF WATER WHICH COOLS THE ENGINE MUST BE

EQUAL TO THE EXHAUST WATER.  IF THE ELBOWS ARE NOT CLEAR THE WATER WILL NOT GET

OUT AND THEREFORE NONE WILL COME IN.

TO CHECK MANIFOLD/ELBOW FLOW, CONNECT A GARDEN HOSE INTO THE INPUT HOSE FOR EACH

 SIDE OF THE MANIFOLD SET OR ONE ON THE IN LINE ENGINES.

 IF A SECONDARY RELIEF HOSE GOES TO THE ELBOW, USE A VISE GRIP ON THE HOSE TO BLOCK THE FLOW.

 

NOW THE TEST.  WITH THE FULL CITY WATER FLOW INTO THE MANIFOLD AND PASSING OUT OF

THE OUTSIDE PROP AND EHXHAUST RELIEF HOLES,  FEEL THE HOSE TO THE MANIFOLD,  YOU

SHOULD BE ABLE TO CRUSH THE HOSE WITH YOUR HAND AND FEEL THE FLOW THRU THE HOSE.

IF, HOWEVER THE HOSE FEELS LIKE IT CONTAINS HIGH PRESSURE AND FEELS IT WILL BURST,  

YOUR EXHAUST SYSTEM IS BLOCKED.  THE ELBOW SHOULD BE REMOVED AND CLEARED OR REPLACED.

 

4) BRAVOITIS

THE WATER HOSE WHICH CARRIES THE WATER FROM THE BELL HOUSING TO THE TRANSOM PLATE

WHEN SUBJECTED TO SALT OR BRACKICH  WATER FORMS A CORROSION OUTSIDE THE END OF THE

HOSE WHERE IT PASSES THRU THE TRANSOM PLATE CAVITY.  THE CORROSION PRODUCES A CRUSHING

PRESSURE WHICH CLOSES THE TIP OF THE HOSE AND THE INTERNAL HOLLOW PLUG.  THE REDUCED

INSIDE DIAMETER LIMITS THE FLOW UP TO 80% WHICH STARVES THE SEA WATER PUMP.  THE

RESULTANT LOW FLOW IN THE PUMP REDUCES COOLING AND FRICTION HEAT INCREASES.  THE RUBBER

IMPELLER DOES NOT LIVE LONG  WITH THE HOT WATER.  IMPELLERS WITH BLADES CRACKING AND

FALLING OFF WITH NO OBVIOUS REASON IS USUALLY THIS PROBLEM.  ANY BRAVO WITH HAVING THE

ENGINE REMOVED FROM THE BOAT, OR TRANSOM PLATE BEING REBUILT SHOULD ALWAYS HAVE THE

IM654 KIT INSTALLED FOR PREVENTIVE MAINTENANCE.

5) THE IMPELLER PUMP

THE PUMP ITSELF CAN BE THE TROUBLE FPR THE OVERHEATING BUT THIS IS THE FIRST THING

CHECKED.  WITH THE PLASTIC BODY PUMP A KIT IM3909H SHOULD REPAIR THE PUMP. THE BRASS

GEN 7 496 PUMP TAKES A DIFFERENT KIT IM496.  SOME PUMPS HAVE DAMAGE TO THE BODY

ON THE ENDS OF THE IMPELLER HITS THE END OF THE BODY CAUSED BY SAND SPINNING INSIDE

BETWEEN THE IMPELLER AND CASE IF THE DAMAGE IS THERE THE IM496REB KIT IS NEEDED

6) UNEVEN ELBOW TEMPERATURE

IF AFTER THE ENGINE IS COOLING PROPERLY, PUT YOUR HANDS ON THE ELBOWS AND SEE THE

HEAT FROM EACH.  IF ONE IS HOTTER,  THE T/STAT HOUSING IS FAVORING ONE SIDE WITH

MOST OF THE WATER.  IF YOU TAKE FOUR PIECES OF 5/8" WATER HOSE APPX 3 INCHES LONG

AND INSERT  THEM INTO THE FOUR WATER HOSES FROM THE HSE TO THE MANIFOLD AND TO THE ELBOW.

THESE HOSES WILL RESTRICT THE FLOW AND CAUSE THE WATER TO EVEN OUT.

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