1996 7.4L Not getting water to the thermostat / no exhaust bellows?

[TBarCYa]

I'm in the final stages of getting this boat back in the water and I've found a few problems. It's a 7.4L with a Bravo outdrive and I'm not familiar with Bravos.

The first issue is that I am not getting water to the thermostat and therefore no water out of the exhaust. Since I don't know the correct terminology, I'm referring to the raw water pump being in the drive, the lower water pump being on the engine by the fuel pump and the engine water pump being the one on the engine. Please correct my terminology tho so I know what I'm talking about.

I'm running on the muffs so the first thing I'll be replacing is the raw water pump in the drive but I would have expected that the hose would provide enough pressure to get water to the lower water pump regardless. All of my water is shooting out past the muffs so it's obviously not going anywhere I need it to. For the lower water pump, how prone are these to failure? I imagine that, like the engine water pump, there are no rubber vanes to go bad so unless it's leaking it should be pumping water, right? So far I have only pulled one of the hoses from the thermostat to the manifold and there was steam but no water. Once things cool down I'll pull some other hoses to see if there really is any water getting to the lower pump.

For the exhaust... There's no bellows from the port on the gimble to the drive. I doubt this is normal but this is how the previous owner ran it so I have to ask... Shouldn't there be an exhaust bellows or is it ok to run without it? There's a short rubber hose attached to the gimble that's not torn, it looks like it's supposed to be that way but it doesn't attach to anything and has the exhaust exiting directly at the drive.

Thanks for your help. We're hoping to have the boat in the water this weekend but it's not looking good unless the raw water pump fixes the water issue.

 

[harringtondav]

The raw water pump in the lower unit is a rubber vane pump, and they are subject to wear and failure. So I'd start there. The exhaust bellows is designed to be in place, so I'd also replace it. Running without it won't hurt, but it could allow a big backwash wave to enter and rise up to your exhaust manifold. Not a good thing.

 

[TBarCYa]

That's what I was thinking... The manifolds and risers are brand new and I definitely don't want to have to replace them any time soon. Is the lower water pump also a rubber vane pump? It's hard to tell from the pics I'm seeing online.

 

[GA_Boater]

Mercruiser exhaust comes in one of two flavors;

Exhaust bellows for thru-prop exhaust oran exhaust tube which doesn't exhaust through the prop. Both work OK and an exhaust bellows equipped drive is a little quieter on plane.


I'll let a more Bravo experienced folk weigh in on the pumps. What does your manual show for your Bravo version?

 

[metsfan3197843]

I don’t believe you have a sea water pump in your bravo drive, it’s mounted on the motor. At least that’s how it is on a bravo 3 It is a rubber vaned pump

 

[Scott Danforth]

ALL STOP.

ya-all gotta read the details.

Bravo drives have the raw water on the motor.

Alpha drives have the raw water in the drive.

OP has a Bravo based on post #1

I'm in the final stages of getting this boat back in the water and I've found a few problems. It's a 7.4L with a Bravo outdrive and I'm not familiar with Bravos.

since this is a Bravo drive, the raw water pump is driven off the crank via a belt.

has the transom shield been checked for "bravoitus"?
has the raw water pump been serviced, if not, start there.

while I would love to have you pull apart your lower unit looking to replace the impeller, I am not that cruel.

 

[tpenfield]

^^^ What Scott said . . .

First thing would be to open up the sea water pump (probably lower starboard front side of engine) and see what the impeller looks like. If it is trashed, then a backflush of the intake hose that leads up to the engine is in order to make sure you got all the bits and pieces out, because there are 2 coolers along the way between the sea water pump and the thermostat housing.

Replace the impeller put it all back together and see if you are now getting water through the engine.

 

[TBarCYa]

Ok... So what's "bravoitus"?

I called a buddy who told me about the lack of a water pump in the lower unit. I'm really glad I didn't have to take that apart. I hooked a hose to the flushing connector and got water rushing out of the lower unit so I'm clear thru the gimbal. Tomorrow I'll replace the impeller and check for pieces blocking up the coolers.

I'm a bit leery of the flushing adapter tho because where it's located the water has the potential to run down and out the lower unit rather than going to the raw water pump. I suppose once the pump is sucking the water will head that direction. Maybe putting the muffs on the lower unit will slow that direction down enough that the impeller will be wet when I start it.

 

[tpenfield]

Bravoitis is a situation of corrosion in the transom assembly where the inlet house comes through. The corrosion expands and strangles the inlet hose/fitting area, essentially choking off the water flow to the sea water pump.

The results is little water and overheating. Google some images of bravoitis and you will see.

 

[Bt Doctur]

Avoid the so called flushing adapter , use the correct ear muffs and you`ll be just fine. Replacing the impeller is not difficult ,
getting to the bolts to remove the pump might be. Once on the bench it`s a snap to repair. Just remember the location of the hose clamps

 

[thumpar]

Do you know which pump you have? Some were built into the fuel pump. I have the one that uses the one piece housing and it's own unit so that is all I can comment on. They are not hard to replace the impeller in. You may want to pull it out before ordering parts. If the housing is pitted you can get a kit that has everything included.

Getting it out can be a challenge depending on access your boat. Once you do it a couple times you can do it by feel. What I do is remove the hoses, the pulley and then the 3 nuts that hold the pump to the bracket. pay attention to which side it up for reassembly. You can get it out of the boat at that point to work on it in a better spot.

 

[QBhoy]

Hi there.
Fine advice above there. Your boat, most likely has the engine driven water pump....a great thing in most circumstances, but not such a great thing, if using the wrong muffs. Even at the best of times and the right muffs, any engine driven pump, whether It be Merc or VP, has a real hard time pulling water up from the muffs on the drive...especially if they are wrongly or poor fitting.

 

[TBarCYa]

My water pump does drive the fuel pump and I got the full kit with the new housing. As far as the muffs, I have the rectangular muffs that seem to fit well but may not. I'll find out later today just how bad of a job this is...

 

[Scott Danforth]

Many times when running on muffs you may need to use duct tape to hold them. Also, use the biggest hose you have and turn the spiggot on full

 

[Lou C]

​ Use these, the best....

 

[Lou C]

I have found that the dual rectangular ones are made out of rubber that is too stiff to seal well. The Merc/Quicksilver ones are made out of much softer rubber and seal much better.

 

[TBarCYa]

After watching some videos I decided to change the pump in the boat I figured that the next time I have to change it I may be on the water so it's better to figure it out now

It's not a bad job. The old impeller was trashed as was the two piece housing I got all of the chunks put of the cooler and hoses and test fired it with the hose disconnected and there's plenty of water now.

Today she goes into the water for the first time since I've owned her. After 8 months of work she's finally ready enough to use. Wish me luck