4.3 engine mounted raw water pump inquiry

[Putz463]

Hello Mercruiser owners with Engine Mounted raw water Pumps OR members here that have a real understanding of or have worked on or installed these systems. I'm looking for some real world experience/input please. I have a 73 Mako23 I/O with a carburated, electric fuel pump, raw water cooled, reman Michigan Motorz (300+hrs now) 4.3 w/A1G2 outdrive all pretty much OEM. I use the boat early and late season (read, in freezing temps) and recently had an outing interrupted by a failed (lower unit mounted) impeller, along with spending the rest of winter basically rebuilding or replacing my motor I'm considering switching the system to Engine Mounted raw water Pump. Re; it seems to me that in an event not unlike what my crew and I went through this past weekend that if the pump had been inside the boat that I would have had fighting chance to not burn my motor up while saving life and limb. In a very topical internet search it looks as though the parts/system exists, is used in some boats, wouldn't be too difficult to install (I have a deep mechanical background and in-house machine and welding dept)...I'm open to any yeah/neah input regarding the idea. Aside; 1 thing I couldn't find definitive info on is whether the EMP system needs the lower unit pump to lift the water initially OR does the EMP alone have enough pull to draw the water all the way up to it's inlet from the LU. Again, any input appreciated, thanks in advance.

 

[Scott Danforth]

first, welcome aboard

second, if you want an engine mounted raw water pump, you need a separate pickup for the motor and you still need to maintain the impeller in the lower unit for exhaust cavity cooling.

or, simply pull your drive every year like you are supposed to for the normal maintenance, and every 3-5 years throw in a new impeller.

 

[Lou C]

Agreed I have not had problems with impeller failure at all with my OMC Cobra drive and I’ve been changing the impeller every 3 seasons (even then there is only minimal wear). I think if anything drive mounted impellers are less prone to failure because the drive is always submerged in the water unlike an engine mounted impeller which is more susceptible to air leaks into the water supply.

 

[Bondo]

Hello Mercruiser owners with Engine Mounted raw water Pumps OR members here that have a real understanding of or have worked on or installed these systems. I'm looking for some real world experience/input please. I have a 73 Mako23 I/O with a carburated, electric fuel pump, raw water cooled, reman Michigan Motorz (300+hrs now) 4.3 w/A1G2 outdrive all pretty much OEM. I use the boat early and late season (read, in freezing temps) and recently had an outing interrupted by a failed (lower unit mounted) impeller, along with spending the rest of winter basically rebuilding or replacing my motor I'm considering switching the system to Engine Mounted raw water Pump. Re; it seems to me that in an event not unlike what my crew and I went through this past weekend that if the pump had been inside the boat that I would have had fighting chance to not burn my motor up while saving life and limb. In a very topical internet search it looks as though the parts/system exists, is used in some boats, wouldn't be too difficult to install (I have a deep mechanical background and in-house machine and welding dept)...I'm open to any yeah/neah input regarding the idea. Aside; 1 thing I couldn't find definitive info on is whether the EMP system needs the lower unit pump to lift the water initially OR does the EMP alone have enough pull to draw the water all the way up to it's inlet from the LU. Again, any input appreciated, thanks in advance.

Ayuh,..... Welcome Aboard,...... So what, exactly happened,..??
How long ago was the drive mounted pump serviced,..??

 

[Putz463]

Appreciate the welcome and input. I hope to learn more about EMP's from those more about experienced than I. I do impeller/LU service every 3yrs as I've always done. The 2yr old OEM impeller lost all it's vanes. Boat ran flawlessly on Saginaw a few weeks ago, sat draining/drying out in my heated shop since then, 32*f air temp all the way to the lake (1hr) this past Sat morning, no ice at launch. Left was taken out 2yrs ago, right taken out Sunday.

 

[Rick Stephens]

A pump in the outdrive is submerged and less likely to get freeze damage than an engine driven pump on cold days.

Like you, I live where I often go boating during cold times. I'm pretty good at draining everything when I pull a boat.

 

[Putz463]

I'm trying to understand your suggestion "you still need to maintain the impeller in the lower unit for exhaust cavity cooling." How is the LU pump doing this? It's my understanding that the lake water in contact with the LU and exhausted warmed cooling water is maintaining the exhaust cavity temperature and (from doing my homework, no in hand experience) that the EMP system' cooling water flows through the motor and exhausts the same way.

 

[tpenfield]

Not sure an engine mounted pump would solve your problem, as they too can/do have impeller failures.

 

[Scott Danforth]

I'm trying to understand your suggestion "you still need to maintain the impeller in the lower unit for exhaust cavity cooling." How is the LU pump doing this? It's my understanding that the lake water in contact with the LU and exhausted warmed cooling water is maintaining the exhaust cavity temperature and (from doing my homework, no in hand experience) that the EMP system' cooling water flows through the motor and exhausts the same way.

you still need the pump in the lower unit to move water thru it.

part of the instructions when adding a heat exchanger is to add an engine driven raw water pump for more flow, however to cut the hose from the drive to transom and continue to maintain the lower unit impeller for exhaust cavity cooling by keeping the water flowing in the drive.

how many years did the impeller you bought sit on the shelf?

factory mercruiser impellers should last well over 5 years from date of manufacture.

 

[kenny nunez]

As Scott said the water needs to cool the upper gear housing that is getting heated from the exhaust system, the oil in the upper is getting over heated.
Volvo AQ drives have a impeller on the propeller shaft that continuously circulates the oil from the lower to the upper to keep the oil cool.
Marine Power has both belt and crankshaft nose driven raw water pumps. If you have 4”-6” in front of the crankshaft the the crankshaft nose style is the easiest to service.

 

[Putz463]

Following up, again thank you all who shared info regarding my pump inquiry. Found this thread on another forum and it answers pretty much all hopes/thoughts/concerns about adding an EMP to my 4.3, including pulling cooling water up through the alpha system to cool the upper/gears. A good read if you so choose. I'm open to continued input if anyone here sees anything in it that is grossly over/under stated or flat out wrong. Now onto getting into the engine and understanding the extent of the damage, fingers crossed.

Good news about crank driven sea water pumps - Offshoreonly.com

Do It Yourself, Boating on a Budget - Good news about crank driven sea water pumps - Moving from pre-Alpha to Bravo required a complete re-design of my cooling system for twin SBC's. The popular favorite is the Mercruiser belt driven sea water pump that mounts on a bracket on the starboard side...

www.offshoreonly.com

 

[Scott Danforth]

Following up, again thank you all who shared info regarding my pump inquiry. Found this thread on another forum and it answers pretty much all hopes/thoughts/concerns about adding an EMP to my 4.3, including pulling cooling water up through the alpha system to cool the upper/gears. A good read if you so choose. I'm open to continued input if anyone here sees anything in it that is grossly over/under stated or flat out wrong. Now onto getting into the engine and understanding the extent of the damage, fingers crossed.

Good news about crank driven sea water pumps - Offshoreonly.com

Do It Yourself, Boating on a Budget - Good news about crank driven sea water pumps - Moving from pre-Alpha to Bravo required a complete re-design of my cooling system for twin SBC's. The popular favorite is the Mercruiser belt driven sea water pump that mounts on a bracket on the starboard side...

www.offshoreonly.com

but you are not moving from an alpha to a bravo. so your premise is flawed.

if you stick with an alpha and add the crank driven raw water pump, you still need to maintain the raw water pump in the leg.

 

[achris]

but you are not moving from an alpha to a bravo. so your premise is flawed.

if you stick with an alpha and add the crank driven raw water pump, you still need to maintain the raw water pump in the leg.

I wonder if it would be possible to remove the drive impeller, maintain everything else in the drive (properly sealed up impeller housing, all the hoses, etc), then add the crank driven pump in the line between the transom plate and thermostat housing. That would have the advantage of pulling water through the drive (to help with the upper housing cooling) and the added volume and serviceability of the new pump... Sort of like the drive pickups in a Bravo drive...

???

Chris...

 

[76SeaRay]

After a lot of research, I decided to go with a Y connection for seawater with one leg of the Y for a seawater pick up outlet as primary flow for the Seawater Pump and the other leg for the Alpha One internal pump outlet. Both are providing flow to the system in normal operation. I am running a GM 5.7L vortec engine by the way so my comments are referenced to that set up.

Most Seawater Pumps require a higher flow than the Alpha One supply line provides, however, a big reason for this Y set up is to be able to run the engine on the trailer using muffs on the Alpha One and a shutoff valve on the Seawater pickup. That's nice to have for tuning your engine and makes it a lot easier to flush the engine out of the water. You also don't have to figure out how to dump the water flow from the Alpha back overboard if you aren't using that flow to do more than aid in cooling the Alpha. The other thing to consider is if you are using closed cooling system which typically (but not all systems) requires a higher flow volume of water provided by a Seawater Pump with a seawater pickup should give better performance for the system.

There are two types of Seawater Pump that I have found, the Mercruiser stock style pump and the Crank Mount pump. Mercruiser Pumps are few and far between and expensive if you find them. The Crank Mounted Pump is nice but without making up your own bracket, it has to be mounted so the inlet and outlet hoses from the seawater pickup are on the port side using the currently available bracket. In my case I don't have the room on that side so I have a stock Mercruiser Pump on the starboard side. Again, in my case, a GM 5.7 vortec engine so yours may be different.

As everyone has stated, the impellers must be maintained properly no matter how the pump/pickup system is designed and which pumps you use.

 

[Scott Danforth]

I wonder if it would be possible to remove the drive impeller, maintain everything else in the drive (properly sealed up impeller housing, all the hoses, etc), then add the crank driven pump in the line between the transom plate and thermostat housing. That would have the advantage of pulling water through the drive (to help with the upper housing cooling) and the added volume and serviceability of the new pump... Sort of like the drive pickups in a Bravo drive...

???

Chris...

if the passages were opened up maybe. otherwise the added inlet restriction may be problematic.

 

[kenny nunez]

Mercruiser recommends keeping the drive impeller when using a crank driven pump and drawing water from the bottom of the hull connecting the drive pump via a “Y“ pipe arrangement.
When I bought my Donzi half the blades were missing in the crank driven pump because the crank pump was pulling a vacuum on the drive pump.
I set it up as Mercruiser instructed with “Y” pipe arrangement, needless to say it worked perfectly. The drive flush out muffs was all that was needed also to run the engine on the trailer.
It was not necessary to even close the sea suction valve to flush it out.

 

[Putz463]

Thanks for sharing your ideas and experience, all good food for thought. achris's "I wonder if it would be possible to..." is basically my train of thought and the direction I'm continuing to study, something along the lines of a modified mini-bravo system w/o breaching the hull to install a thru hull/p-u. ScottD's suggestion about restriction & possible opening is valid, It does seem that the ~1/2" riser tube coming out of the Alpha pump would be a pinch point restriction since most of the crank pumps I'm finding have 1 1/4" in/outlets would seemingly create negative pressure on the inlet. Doing math on flow rates for 1/2"id tube/pipes shows ~7-14gpm pressure dependent and the ~11gpm/1k rpm of the Merc pumps so ~33gpm@cruising 3k rpm needs that ~1-1.25"id passage. Not a deal kill, just a factor that needs to be realized and managed.

How Much Water Can Flow Through A Pipe (GPM/GPH)?

Three tables to get a general understanding of water flow capacity through a pipe or roof drain. If you have questions, contact our roof Drain Wizard.

hy-techroofdrains.com

 

[Scott Danforth]

You do realize there are literally many millions of boats with an alpha drive that when maintained, last many decades.

I do believe that your impeller may have been older than you thought when you installed it.

since the drive comes off every year for maintenance, changing the impeller every 2-3 years would be less work and cost.

or switch to a bravo drive if you want to keep it mercruiser

 

[Putz463]

I do realize this, thanks for reminding me of it, but how many of those millions of them find themselves hunting 1/2 mile out in Lk MI in mid winter with their nephew in the layout boat 200yrds away when Lk MI winds kick up, shift ~90* and start throwing 3-4' rollers at you that are starting to break and smoke is rolling out of their doghouses. And then find the "new" 2yr old OEM impeller might have been "stale" past its sell by date that might have ruined a new 3yr old motor? Situations like these leave lasting impressions. Thus exploring the idea of getting a reasonably easy & quickly serviceable impeller in the boat. So, trying to understand how swapping a Bravo for this already inplace Alpha would be less work and cost than an ~$200-300 pump, some hoses and some custom brackets/plates made in house in my machine shop?

 

[Lou C]

I’ve never used my OMC Cobra in winter conditions but over the 20 years of boating in salt water I have never had an overheat due to impeller failure. I did have an episode of warmer than normal running due to sucking up sand. I normally change the impeller every 3 years and they look almost like new.
The only overheat I ever had was due to a raw water intake hose popping off the P/S cooler mounted behind the engine. So that’s something everyone who owns an inboard should check at the start of every season. All hose clamps in the cooling & exhaust system.