How to cool BravoIII with thru-hull water pick-up

S

shore

New Member
Jul 18, 2009
439
port orange florida
Boat Info
1996 290 Sundancer
Engines
Twins and a Gen
I'm changing my 7.4 BIII raw water drive pick-up to thru-hull water pick-up to avoid the transom hose issue again.

This is all pretty simple but my question is how to cool the internals of the BIII?

A drive shower is cheap enough but that does not do much for the internals.

I know this is a common mod but noone mentions in detail how to cool the drive with the transom hose dissconnected?
 
Cut the hose between the drive and the bellhousing and remove at least a 2-3" piece - you can access the hose by turning the drive hard over - just be sure to be very careful not to nick/cut the bellows:smt089 when you are cutting the hose - some people remove the entire upper section of the hose but it is hard to get to and you need a special tool
 
Henry's mechanic installed a T fitting. He is using both the B3 water pickup and a thru hull water pick up. The drive showers are suppose to cool the Bravo drives between 30 and 50 degrees depending on which shower you purchase.

Shore,
What problems did you have with your B3 PU hose?
Nevermind... I just looked up your thread.
 
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Someone correct me if I'm wrong, but don't you just leave the hose open so the water just flows into the drive the normal way and then up and right back into the ocean?

Ididntdoit - is that what you meant? Sorry if I'm just repeating what you said.
 
Dennis,

That is one way that it is done. although it is a little more complicated. A plug has to be installed in the transom to block where the hose goes through. Mercury sells a kit to do just that. Then you install a trough hul and connect that to the engine water pump.

Now comes the interesting part. When we were going this route last year my tech contacted Merc to make sure he had the right diameter for the engine. He was told that the recomneded practice was to install a tee inside the boat connecting both the water line from the drive and a new through hull. I ended up adding two tees so that I could have a flushout fitting.

I don't know the rationale for the recommendation. The shop that does my service was going to cut the hose and plug the transom as they had done in the past many times, and in fact the owner's boat is set up that way. My observation is that Mercury is very conservative from an engineering perspective with a healthy case of CYA thrown in for good measure.

My recommendation would be to contact Mercury to hear what they say about the specifics of the boat. It may be that the 496 is a special case, and older/smaller engine designs can go the cut and plug route. It's doubtful they will come out and say that the cut and plug method is bad (CYA from potential claims for boats already modified), but if they are overly insistent read between the lines.

Henry
 
OK thx guys..here is what I taking from this.There are two suggestions

1..You are saying to just leave a foot or so of hose from the transom connected and plug the end of it?
I only need about 2' for my new thru-hull pick-up spot so there is plenty of hose.

2..Get a T-fitting for the intake hose from the transom AND the thru-hull.Therefore letting water still flow through the drive but primarily from the thru-hull?

I just don't understand how that amoutn of hose is going to let the drive cool internally.

I have about 3.5' of intake hose from transom to sea-water pump.I pulled the hose off the transom and shoved my house water hose into it...the water out the exhaust was twice as much.The manifolds/risers where warm to the touch now.prior you could not touch them more than a tap.
 
Aw geez, I get it....you're talking about cutting the hose BETWEEN the drive and bellhousing and letting the momentum of the boat moving force the water through the drive to cool...that makes sense.
 
Lazy Daze said:
Someone correct me if I'm wrong, but don't you just leave the hose open so the water just flows into the drive the normal way and then up and right back into the ocean?

Ididntdoit - is that what you meant? Sorry if I'm just repeating what you said.
Click to expand...
I had read the install procedures on the Bravo block off kit somewhere. They pulled the water intake tapered insert out. And cut the hose off closer to the inner transom plate. Then installed the water blockoff plate in place of the 1 1/4" hose barb fitting for the water intake hose that goes to the seawater pump.
So Yes Lazy Daze. Once that hose is removed or cut. Its all open ocean. Just a plate installed to keep the open ocean from flushing your Bilge and ER
 
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A) Never use brass because it will corrode, fail and sink your boat. Use bronze hardware instead, properly linked to the boat's bonding circuit.

B) If you don't want to remove the drive, then install a tee in the line and let the throughhull do the heavy lifting for the engine cooling.

Henry
 
shore said:
Aw geez, I get it....you're talking about cutting the hose BETWEEN the drive and bellhousing and letting the momentum of the boat moving force the water through the drive to cool...that makes sense.
Click to expand...

well i think i'm with you on this. i have just installed a new b3 on our old boat and so far will be going with the sea water from the drive and not installing a sea-cock for cooling.

what i don't understand is tailchaser. if you remove the hose barb and block your not going to get any water in the inside of the drive to flow?? don't you still need to cool the drive fron the inside?

as a side note i had a drive shower on A1 and realy didn't see any help from it.
 
Yes, sorry, I wasn't as clear as I should've been - simply leave the drive side open. Thanks for the corrections. I agree it's a good idea to do the block-off thing at the transom.
 
shore said:
Aw geez, I get it....you're talking about cutting the hose BETWEEN the drive and bellhousing and letting the momentum of the boat moving force the water through the drive to cool...that makes sense.
Click to expand...
Check out clamshell scooper thru hulls for water intakes.
I saw another setup used on performance boats.
There made out of stainless tube. L shaped. They go thru the transom, Then drop down about 1/2" below the hull bottom for the water PU. Same principle as how the drive showers work. No strainer like the clamshell. But nice if you have trl bunks and stringers in the way for going thru the hull clamshell setup.
 
I think he thinks he needs to pull the drive to install the block off - he does not just remove the water neck and install the block off from inside the boat
 
garryowen said:
well i think i'm with you on this. i have just installed a new b3 on our old boat and so far will be going with the sea water from the drive and not installing a sea-cock for cooling.

what i don't understand is tailchaser. if you remove the hose barb and block your not going to get any water in the inside of the drive to flow?? don't you still need to cool the drive fron the inside?

as a side note i had a drive shower on A1 and realy didn't see any help from it.
Click to expand...
garryowen
Water will still go through the pickup strainer holes in the lower unit. Your only removing a rubber water supply hose that gets water from the outer transom assembly to the inner assemble where it can be picked up by the engine seawater intake hose.
The test I read about on the drive showers. They put temp gauges on the Bravo drives for checking lube temps. Mostly performance boats run in warm water. Basically, If your drive has white mineral deposits on it. Its running so hot the ocean/lake water is boiling on it. If not, Your most likely OK. On there test, They were reaching temps of 280 degrees or more. They cooled the drives 30 degrees with a single and 50 degrees with the double water PU showers.
 
shore said:
I'll brass plug the leftover hose inside the boat before I pull this drive off AGAIN..lol
Click to expand...
I think installing a one way check valve would be really cool.
Then you could install a bilge pump to it.:lol:
 
ok; when talking about the bell housing your referring to the one in the transom and not the back of the motor.
when blocking the the transom intake on the inside then you remove the hose in the transom-bell housing. this lets the lake water pull threw the drive intake holes and spill out on top of the bellows where transom hose is now removed from.
this give enough flow to cool drive?

sorry i didn't get the first time( if i still don't please bear with my and keep explaining)

as a note on the drive shower; the last drive i locked up, i had just checked for temp. and when it locked the first thing i did when boat stopped was reach down from swim platform and see if it was hot. also lake temp was 65*
any how drive shower on last drive didn't let it live any longer than the first two.
 
garryowen said:
ok; when talking about the bell housing your referring to the one in the transom and not the back of the motor.
when blocking the the transom intake on the inside then you remove the hose in the transom-bell housing. this lets the lake water pull threw the drive intake holes and spill out on top of the bellows where transom hose is now removed from.
this give enough flow to cool drive?

sorry i didn't get the first time( if i still don't please bear with my and keep explaining)

as a note on the drive shower; the last drive i locked up, i had just checked for temp. and when it locked the first thing i did when boat stopped was reach down from swim platform and see if it was hot. also lake temp was 65*
any how drive shower on last drive didn't let it live any longer than the first two.
Click to expand...
You have it right.:thumbsup:
Might even get more cooling. There is no cooling going through the rubber hose. With it removed, Now the water gets picked up and sprayed all over the bellows, drive, etc.

Very hard not to break the Alpha drive behind your 7.4
Your twisting shafts and breaking gear teeth. Its not a temp or lube related issue. The 1.32:1 GR ? Had thicker teeth on the gears helping that Alpha survive. Now there's only the 1.47:1 GR for the V8.
Another benefit of the stronger Bravo drive is being able to run a 2.0:1 or 2.20:1 GR is it puts more tq to the prop. Not a chance being able to run them GR's on a Alpha 1 drive without killing it fast. I put the 2.20:1 behind my 8.1 Mag. Going for max TQ to the prop.
 
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