Ahhh....Finally Enough Water (Dreaded BIII transom clogs)

W

William Miller

Member
Mar 16, 2007
327
Darnestown, Maryland
Boat Info
290 AJ
Engines
Twin Mercruiser 300 hp Bravo III
After a few seasons of chasing down overheating issues, (Manifolds, pumps, impellers, thermostats and such) I decided that the issue could almost only be the transom hose or elbow inside the transom on the raw water line was clogged or partially obstructed.

Instead of hauling the boat and removing the drives and such, I decided to install new seacocks, and strainers plumbed straight to the back of the engine raw water pump. The seacocks are a 3 way valve made by forespar and have a garden hose attachment to allow for flushing and winterizing. Seacocks are 1-1/4". Used 1-1/4 engine exhaust hose to forespar strainers that are the size of a swimming pool strainer. Then about 5' of hose to the intake of the pumps..... I also installed some big clam shell intake scoops on the bottom of the hull.

This was a fun project over the holiday weekend while my boat was on the lift. Help from the passing hurricane lead to ultra low tides in the upper chesapeke.

The best was immediate gratification the minute I started the mains. I had water pressure showing on the smart craft display that I had never seen before!

What a great feeling that this whole issue is behind me and I will have time to have fun on the boat and attend to other stuff!

Fixing the original design would have been such a waste of time. I just cant imagine that mercruiser has not come up with something better.



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Hopefully you shut down the water supply transom assembly setup from both ends because that will rot out at the water fitting on the transom assembly and leak into your boat. Thru hull is all that's needed for the motor. Cut the water line at the bell housing so the B3 can circulate water and cool itself.
 
Thanks!
I spoke to mercruiser about this a few weeks ago.
I have a temporary plug in the red inlet water line (Its where the quick connect fitting was before under the exhaust manifold.)
Boat's on a lift so it can't sink at the moment.
I ordered the block-off plate kit that replaces the 90 deg fitting. (not sure i can get back there to make the swap out.)
Any suggestions? Actually this was one of the reasons I chose to do the thru hull intakes.

Mercruiser mentioned about cutting the hose and letting the water splash to help cool the drives.
I wonder how much comes out?
Once the hose is cut at the outside of the transom plate, is there something on that side to close up the hole?

Thanks for your input!
 
Since there is no water pump in the drive, if you cut the hose there won't be any water flowing to "splash to help cool the drives". Not that the water was really used to cool the drive in the first place - I'm sure there was some parasitic cooling, but nothing significant since it was just a straight pipe up to the transom with no cooling passages in the drive. You can always add drive showers if you are concerned about cooling them.

Edit: After reviewing some more information it looks like (a) there's a lot more water circulation in the drive unit than I thought, and it could be significant for cooling and (b) at speed, water would probably be forced through the drive without a pump. Sorry for speaking before knowing.
 
Last edited:
I used a plug and a hose clamp on the outside water line and 9"needlenose vise grips on the inner water line.
 
Bill,

The through hulls was a good idea. I would caution you to be careful in removing the gooseneck. In the picture below you can see where it mounts.



To get at this you may have to move the steering rack. The issue is that the clogging you experienced is probably at the gooseneck mount on the outer transom plate. The gooseneck itself is plastic, the two bolts that old it on are stainless. The outer transom ring is aluminum. The risk is you can unbolt the gooseneck and the threads will come out of the bolt mounting points and the mounting surface will be corroded. If that happens its new transom ring time. Figure $ 4500 per drive for parts and drive, transom ring and engine removal. So the short version is be very gentle in removing those bolts.

Henry
 
If you block off the water from the inside and outside, there is no need to remove the gooseneck, even if its rotten.
 
scoflaw said:
If you block off the water from the inside and outside, there is no need to remove the gooseneck, even if its rotten.
Click to expand...

The point is that if it is rotten, the gooseneck will eventually leak between it and the transom plate at the the interface. If he carefully takes off the gooseneck without damaging the threads, the mounting surface can be cleaned up if its early enough. I switched over to a through hull, however I left the waterline from the drive connected on Mercruiser's recommendation. I discovered the gooseneck was leaking last spring and when we took it off assuming it was cracked we discovered the corrosion damage.

Henry
 
If you block it off fore and aft there will be no water at the goose neck. Merc says you only need the duel cooling if your south of the 15th parallel N.
 
First, Ill try and get some pictures this weekend.
I don't think i have as much corrosion as in the picture. but this may be a good reason to wait an install the block off plate at the end of the season. I finally feel like i got my boat back and dont want to screw that up mid season. On my amberjack the back edge of the engine hatch is just over the manifold elbows. im either going to have to take them off and squeese over the top or take the manifolds off so i can squeese between the engines. or take 4 batteries out to get on the outside of the starboard engine. my kid can fit in the back to the port of the port engine. climbing over the waste tank. no easy way. too easy to break off those bolts or pull the aluminum threads out of the transom plate without delicate surgery...

Thanks for the pictures and advise....

Btw i know the bravo unit has quite a large cavity inside the little water strainer holes. It seem like a bad setup / design. Sure it works great when new!!!!
 
I just removed my gooseneck from a 03 300 Sundancer and the hose was good. no corrosion at the gooseneck but there was no gasket, only silicone. Is this from the factory & is there a gasket available? I have been overheating at higher RPM's after getting on plane. Pulling back on the throttle cools it down. I changed the raw water pump with no change. The original impeller was in good shape and it ran great last year which was my first year. I split the outdrive and found barnacles inside the drive. I cleaned it then painted the inside of the drive. The good engine was clogged a lot worse than the overheating engine so I am not sure if cleaning took care of the over heat problem. That is why I pulled the gooseneck to inspect. Please let me know about the gasket.
Thanks,
J-Rod
 
J-Rod said:
I just removed my gooseneck from a 03 300 Sundancer and the hose was good. no corrosion at the gooseneck but there was no gasket, only silicone. Is this from the factory & is there a gasket available? I have been overheating at higher RPM's after getting on plane. Pulling back on the throttle cools it down. I changed the raw water pump with no change. The original impeller was in good shape and it ran great last year which was my first year. I split the outdrive and found barnacles inside the drive. I cleaned it then painted the inside of the drive. The good engine was clogged a lot worse than the overheating engine so I am not sure if cleaning took care of the over heat problem. That is why I pulled the gooseneck to inspect. Please let me know about the gasket.
Thanks,
J-Rod
Click to expand...


I don't know about how it left the factory, but the block off plates I bought did have a gasket.
Do you have pressure sensors with the readout on smart craft. I'm now pushing about 7 psi at cruising rpm and higher.
How did you get back behind the engine to pull the goose neck?
 
update:
Well I have pictures but cant upload them.

While evicting the birds nest from the blower hoses. my son was able to scope out the inner transom plate and goosneck fitting. He thinks he can get to the port side from behind the waste tank. Starboard side might require removing the power steering ram and possibly the two exhaust manifolds between the engines.

My goosenecks have the quick connect fittings like the hose below the exhaust manifold going to the raw water pump intake.
 
On the outside I cut the water supply hoses near where they enter the outside of the transom plates. I will plug the ends that go tward the transom plate. I extended the hoses that come up from the drive housing with a temporary piece of garden hose and routed it up above the swim platform. I wanted to see if they would flow any water while the boat is moving. In fact they do produce a pretty good flow once on plane and s bit more the faster you go. Not really a lot of pressure but about as much as a garden hose with the valve half open. Next plan is to direct that water over the top of the drives like a drive shower.

Next step is to sort out a simpler way to flush the engines using the threeway sea cock.
The trick is that i need to turn on and adjust the hose from dock at the same time as i am starting the engines. If i put full street pressure on without the pump sucking it, it forces the lid on the strainer up and blows out the seal. I have a cheap pressure relief valve that came with my old flushing kit but its fairly delicate. I need to source a relativly low pressure relief that is fairly beefy.
 
Cheapest way: put an inline shut-off valve in the hose a few feet from the end that will be in the boat. Leave the dockside water on and control it from in the boat with the new valve.

I think you have become a paying member of this forum to do pictures? Not sure, though.
 
Its been a while.
Since i pulled the engines anyway. I decided to replace the goosenecks with the block off plates.

Very carefully loosened the bolts and lucky they came out without stripping the heads.
They were NOT stainless.

These pictures confirm the issue.
So glad I installed the thru hulls.
Ill take pictures next time i go to the boat.

NOW...how to clean out the hole and get the hose remnants out.
Once its cleaned out. I was thinking of plugging it with epoxy putty to prevent future corrosion. Then install the block off plates.

Maybe just a pipe plug on the outside.
The hose on the outside is still in the way so i cant see what i will be dealing with.
 

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If you plug off the raw water lines at the transom assembly make sure the water flow through the drive body isn’t impeded. So on the outside you need to disconnect the feed to the transom assembly.
 
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