Cooling 454 with Bravo One Drive

J

j-d

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Friend upgraded the power plant in his Chris Craft Sea Hawk from 350/Alpha1G1 to 454/Bravo1. Both RWC.
But this 454 is a Crusader and he's using a belt driven Sherwood raw water pump connected to the outdrive. Boat overheats and the blades are missing from the raw water pump. Thinking the pump is starving for water from the outdrive.
How should the raw water be connected? I've heard Bravo drives should have a through hull pickup. Is that in addition to the lower unit source or does it replace? If replace, does the hose from the lower unit simply get capped? Does the lower unit cool the upper gearcase through that supply hose? If so, this lower unit came with a drive shower. Would that be sufficient?
Thanks!
 
Well dang, the impeller has to be good or it ain't gonna do a lick of good no matter how things are hooked up.

What size( in /out) fittings on that water pump(gives us an indication of the GPM or pump capacity)

Yup, The drive pick-up cools the drive and YUP, ya gotta add a thru-hull water pick-up cuz the drive pick-up has small diameter passages that restrict water flow.
 
I've owned a 454/Bravo 1 RWC and currently own a 454/Bravo 3 RWC for 10 years that I converted to FWC (both Mercruisers). Only water pickup was/is from the outdrive and never an overheat with either.

I suggest you 1 - find all the missing blades and 2 - check the outdrive for blockage.

I hope this helps.

Bob
 
Charlie,

He wasn't using an old or damaged impeller going into this project and problem. It has destroyed a couple new impellers once launched and then the engine overheats.

Scooter,

The 1-1/4" approach is what I'd like to see him do, and just block the line from the outdrive, not use it at all. That is why I asked if the raw water flowing through the outdrive contributed to the cooling of the upper gearcase and mentioned the outdrive shower.

Bob,

He's flow tested this with a garden hose feeding the gearcase inlet with earmuffs. I wonder if: 1. That's enough water to cool a 454, and 2. If the Sherwood pump could be sucking the "S-Hose" [gimbal to transom] or the transom-to-pump hose [inside the boat] into a collapse.

If the inlet flow to the raw water pump is inadequate for 1. or 2. above [or something we haven't figured yet], it seems that shortage could damage the pump.

Has anybody used two sources, the Outdrive and a Through Hull, connected together?

Thanks!
 
Ayuh,.....

With the Millions of 454s out there sucking their water thru the Bravo drive,......
I gotta believe that your Bud's has some Blockage somewhere Up-stream from the Pump.......
 
JD,
Merc now recommends drive AND thru-hull raw water pick-up.

and yes, it's possible that the pump is partially collapsing the feed hose an contributing to it's own failure.

DON'T block off the drive pick-up.
 
Charlie, You are confirming what I thought I heard [two pickups and don't block drive pickup] and what I suspected [hose from outdrive to boat collapsing or water flow simply inadequate].

Possible wild card here is the Sherwood pump. Its design might make it either more demanding or less fault tolerant than the ones commonly used by MerC.

I'll pass this on and encourage adding a through hull TO the I/O hose.

Just called for the hose size on the Sherwood. It's a 1" pump.

He also confirmed he started this with a new impeller. It trashed that one and another new replacement.

Thanks again, all!
 
if he ads a thru hull inlet, do not block off the line coming from the outdrive. the flow of water does help cool the outdrive. if he ads the thru hull, have him add a drive shower. divert the water from the drive to cool the shower.
 
Merc now recommends drive AND thru-hull raw water pick-up.

JTYBT15 - do you have a service bulletin number or other source for this information? I'd like to look into it further.

Thanks -

Bob
 
I'd like to see that as well. Not, just for the record, that I don't accept what the guys are saying about a second pickup. But I'd like to see if MerC has locations, dimensions and so on.
 
I believe there is a problem with the set up
We run twin 502's with Bravo's all day long at 140 degree's
No problems with the standard Merc water/fuel pump.
The hoses do need to be plumbed correctly however.
Good Luck
Hope this turns out ok for you
The solution will be interesting
 
Charlie -

So you read a service bulletin? Did someone tell you they read a service bulletin?

Thanks -

Bob
 
Sorry guys, I read it here(bulletin) a couple years ago(or more) and set up my alpha to BII swap that way.

If you've done any work on a B cooling system, you know there are fittings that are about
5/8 inch which is very restrictive for a 1" or larger pump.
 
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