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Mercruiser 74 Bravo 2 impeller hell

J

justmyluck

New member
"I dewinterized today and the

"I dewinterized today and the engine got to 200 degrees on the ear muffs so I pulled the cover from the water pump and sure enough, impeller was in million pieces. Always have a spare so I swapped them out , fired up, and no luck. engine started to get hot so shut it down, checked pump again, impeller was in bigger pieces this time. I have replaced the impeller 4-5 times before, the housing is 3 years old, and never had a problem.. The boat is a 1996 Sea Ray 454 Bravo 2. Any suggesions why it would fry a new impeller in a matter of 2 minutes? Thanks for any help."
 
"If water is not actually movi

"If water is not actually moving, the impellors will overheat and wear down or disintegrate.

Are the water feed holes in the leg open to allow water to the pump?

The feed lines above the pump leading to the recirculation pump, and possibly the thermostat housing, may be well clogged with pieces of the previous impellors. A back flush is definitely in order. Also open the thermostat housing and inspect/clean, etc.

Make sure water can get to the recirculation pump."
 
"Ayuh,.....

Backflush the c

"Ayuh,.....

Backflush the cooling system,....
You've probably got Chunks of all those Toasted impellers blocking things up...."
 
"OK I just backflushed from th

"OK I just backflushed from the thermostat and lots of little pieces came out the hose that I disconnected from the raw water pump. Next step is checking thermostat, how is this dismantled and checked?"
 
"I have given up on muffs afte

"I have given up on muffs after losing a couple of impellers the way you have. I fixed up a 5 gallon plasic bucket with a bulkhead fitting and brass hose barb on the bottom with about 4 feet of hose. I connect it to the inlet of the pump whenever I want to run the engine onshore. I keep the bucket full and run the motor with a positive flow of water. This has the added benefit of allowing me to flush with antifreeze for winterizing ( I can't believe I'm even thinking about that now, I must be sick)."
 
"It is my understanding that t

"It is my understanding that the pump would still draw water in if the thermostat were clogged? I flushed water thru both sides of the thermostat, through the hose that goes to the recirculationg pump (water came out thru the thermostat), through the hose that goes to the engine oil cooler, back thru the hose that goes to the outdrive(the intake hose)and my bilge is really clean now. Have I forgotten anything??? All water flows are good and clean. I am going for a new impeller and hook it back up. I will never use drive muffs again! thanks for all suggestions."
 
"adam:

Take two beers and g

"adam:

Take two beers and go boating in the morning!
biggrin.gif
"
 
"Guys; with all due respect, m

"Guys; with all due respect, muffs work just fine if you have enough water flow cranked up. I have used them for 20 years and never lost an impeller as a result of muffs.

Rod"
 
"Ok, had the boat out twice no

"Ok, had the boat out twice no problems with the NEW water pump/impeller. This weekend the temp was fine (165-170) while under 2500 RPM but rose to 210 while above 2500 rpms. got to 210 degrees and stayed there and dropped back to normal when I pulled throttle back a bit. It happened twice so I idled back to the dock. I am thinking thermostat (original 12 years old) or some type of blockage?? Need some suggestions. Only thing I did different was clean the carb and put STP fuel treatment in the tank. Thanks"
 
"Buy an infrared temp. gun; $4

"Buy an infrared temp. gun; $40. Point it to different locations on the engine, exhaust mans. and risers. Also the rubber exhaust sleeves. If the mans and risers are hot, can't lay a hand on them for 10 secs., then they may need cleaning or replacement due to age.

Time for a new T'stat after 12 years. Remove the hsg. from the intake. You probably will find alot of rust and scale buildup inside the hsg. including some partially plugged hose outlets. I removed the scale and rust w/a Dremel and 50 grit sanding sleeve.

Check the exhaust shutters for damage preventing them from opening completely to allow hot water to exit."
 
"Replaced thermostat, same pro

"Replaced thermostat, same problem. I took a temp. gun and everything is 110-120 (dash guage showed 160) on port side but starboard exhaust elbow got to 175. manifold stayed at 125, hoses 125, y pipe 150. I checked water flow thru the ENTIRE system and eveything is great. What is next??"
 
"Bill:

"exhaust elbow g

"Bill:

"exhaust elbow got to 175." Too hot.

You could use longer hoses to switch T'stat hoses to the risers and see if the hot riser changes sides. If it does then the issue would be weak water flow out of the T'stat Hsg.

Remove internal parts, reinstall gasket and top and secure w/different bolts, washers and nuts. Plug openings w/plumbers puddy except the base. Lay it top down and fill the T'stat Hsg. with muriatic acid (pool supplies) for 90 minutes, rinse and pressure flush it--BIG DANGER FOR SEVERE BURNS; USE RUBBER APRON, GLOVES AND FACE SHIELD. KEEP A RUNNING WATER HOSE AT HAND WHEN USING THE ACID!!!!! KEEP IN PLASTIC 5 GAL. BUCKET IN SECURED, VENTILATED AREA OR DO NOT LEAVE UNATTENDED.

Did you check the exhaust shutter at the top of the "Y" pipe?

Riser may not be getting enough cooling water or it is partially plugged. Pull it off, check for damaged gasket, check for buildup of internal crud and check the shutter while it's off.

Even if it LOOKS clean, remove brass fittings and soak in acid, OR plug holes and water jacket w/plumbers puddy and fill the riser with muriatic acid (pool supplies) for 90 minutes, rinse and pressure flush it--BIG DANGER AGAIN so use same precautions."
 
I had the same problem....I ac

I had the same problem....I accidently switched the hoses on the water pump and the impeller was not sucking in enough water the hose pressure on the muffs was keeping one side cool and other side was very hot...switched hoses and it was fine...had to replace impeller again though....good luck
 
"May consider circulating pump

"May consider circulating pump as well. if there is corrosion, the circ pump impeller may be cavatating in its pocket or dissentagrating.
also make sure circ pump suction hose is in good shape and not colapsing with pump suction.
2_cents.gif


Kurt

PS don't run at more than 1500rpm on muffs."
 
"Well, still had overheating p

"Well, still had overheating problems so I pulled the stbd exhaust elbow, riser , rubber ehhaust hoses off. To my surprise there was no exhaust flapper in the opening to the Y pipe. Disconnected the hose ( outside of boat) going to the outdrive at the transom and there I found the flapper in a bunch of pieces blocking the hose. would this only cause the stbd side of the engine to run hot? All other exhaust pieces looked to be in great shape."
 
"would this only cause the

"would this only cause the stbd side of the engine to run hot?"

Oh yes if there was debris blocking the starboard side of the "Y" pipe.
 
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