Cooling Upgrades - affect on bravo 3X drive

wofforduk

Member
Joined
16 Oct 2013
Messages
146
Visit site
okay, 3/4 of my trips this season have been fairly catastrophic... has to be said.

the last trip I think I'm lucky to still have a boat as it melted the exhaust rubber pipe just above the waterline but still leaked badly!

Im going to bypass the Bravo 3's water intake and exhaust completely, this is a decision which I have made and will stick with. CAD files for stainless blanks are already send, and engines removed ready for them to be fitted.

water pick up scoop from hull > stopcock > stainer>impellor>into engine. no messing.

Exhaust from swan neck> water mixer>90 bend>transom 4' outlet above waterline. once again no messing. all 4' rather than any reductions. Yeah i know it will be louder but id rather that than have any of the issues had before..


Anyway question is, do I need to cool the leg down somehow?? Read that for the yanmar 315hp you need the shower... so just curious really! im guessing probably not for the end of the season??
 

MapisM

Well-known member
Joined
11 Mar 2002
Messages
20,374
Visit site
Well, a shower doesn't hurt for sure. With high power/torque engines, it's always a good idea to fit one.
And its cost is minor, in the contest of the mods you are thinking to make.
Alas, be careful with them: you might well be jumping out of the frying pan into the fire.
Straight through transom exhausts must be carefully designed, and depending on the boat/installation, they can be a recipe for hydrolocking the engine.
With a B3x outdrive, a properly maintained standard installation should neither melt the exhaust pipe nor leak.
I'd rather have it checked and fixed by a good Merc engineer, before going for esoteric and risky mods.
Which btw would make the boat much harder to sell, not to mention illegal.... :ambivalence:
Mind, if you are fed up with outdrives troubles, there is one and only way known to mankind to get rid of them for good.
Change the boat and get one with shafts! :D
 

spannerman

Well-known member
Joined
30 Nov 2002
Messages
3,139
Visit site
Its imperative with all Mercruiser drives that the 'S' water hose from the drive to the transom has a good 2" cut out of it so that seawater which flows through the drive and cools it in the process can continue to exit if the water intake to the engine is blanked off at the transom, otherwise the flow stops and oil temp goes up.
And definitely fit a drive shower, we had a series of failures with a customer who had big Yanmars on B3 drives, the problem was the that on the plane so much of the drive was above the water it didn't get enough cooling. Also Askaladden here in Norway had problems with the Commuter with Mercruiser 4.2 engines and Bravo III drives as they found the boat was stern heavy so they added a box section each side aft to increase the stern buoyancy, but this created a low pressure area behind the boat which kept the waterline artificially low around the drive as it sat in a pocket between the two buoyancy extensions, and we had drive cooling problems, so they went to a through -hull water intake and blanked off the transom intake, but the factory people didn't understand how the system worked and didn't cut the 'S' hose from the drive, after about 5 drive failures on new boats at their expense they got the idea. We received several new boats without the mod and during PDI we cut the hose, this mod is in the Mercruiser workshop manual.
 

wofforduk

Member
Joined
16 Oct 2013
Messages
146
Visit site
Thanks MapisM - i have a very good swan neck that comes up probably 14 inches, more maybe above the waterline, so it shouldnt be a problem hopefully, and the outlet will be above waterline too. Not sure if that makes it illegal, didn't realise there were any laws on it...!

Cheers Spannerman, Ill definitely remove the pipe with pleasure, that messed up the system pretty badly as it came loose last time. rubbish system! ill probably just remove the pipe all together, and hope that maybe some water will flow through.

Im looking for a drive shower now. seems a logical solution!! Where can I find one in the uk? Googles not much help for this sort of thing! :D

Cheers
Will
 
Top