Pump redundancy

[Tomtomterrific]

Hi - I replaced my seafarer 5.7 outdrive impeller. I also replaced the crank mounted raw water pump supplied by a seacock. I believe the crank pump is redundant/optional. Can anyone confirm? Also does the GM style water pump also circulate raw water? Thanks, Tom

 

[DennisG01]

We're missing some info... but I'll make an assumption that you have a Mercruiser with an alpha drive? Assuming that...

-- At some point someone added the crank-mounted raw water pump. Probably becasue there was an issue with the standard raw water pump in the drive.
-- The drive pump may actually be disconnected... did you verify if it actually pumps water?
-- The crank mounted pump is superior to the drive pump
-- You will ALSO have a circulating pump on the engine (belt driven). But that is not a raw water pump. That one circulates the water through the engine.

 

[Tomtomterrific]

We're missing some info... but I'll make an assumption that you have a Mercruiser with an alpha drive? Assuming that...

-- At some point someone added the crank-mounted raw water pump. Probably becasue there was an issue with the standard raw water pump in the drive.
-- The drive pump may actually be disconnected... did you verify if it actually pumps water?
-- The crank mounted pump is superior to the drive pump
-- You will ALSO have a circulating pump on the engine (belt driven). But that is not a raw water pump. That one circulates the water through the engine.

Thanks.

Yes alpha 1 gen 1. I’ve replaced the (toasted) lower unit impeller and tested in on muffs and in the water with the seacock for the crank pump closed. It runs at 150-160. So yea it seems to working properly.

The old crank pump was ‘custom’ installed with pipe sections as pulley spacers and fabricated aluminum bushings as mounting spacers.

I cleaned up the install bolting the crank pump directly on the pulley/balancer and used stainless steel spacers on the bracket.

I’m not happy with the install though. It wobbles and appears to be dripping already. It was a Volvo pump and I sourced a matching replacement.

I want to delete it (or get the right OEM crank setup)

Installed to a Merc tech and was told the factory setup was the outdrive impeller and no through hull/crank pump.

Thanks, Tom

 

[Tomtomterrific]

Thanks.

Yes alpha 1 gen 1. I’ve replaced the (toasted) lower unit impeller and tested in on muffs and in the water with the seacock for the crank pump closed. It runs at 150-160. So yea it seems to working properly.

The old crank pump was ‘custom’ installed with pipe sections as pulley spacers and fabricated aluminum bushings as mounting spacers.

I cleaned up the install bolting the crank pump directly on the pulley/balancer and used stainless steel spacers on the bracket.

I’m not happy with the install though. It wobbles and appears to be dripping already. It was a Volvo pump and I sourced a matching replacement.

I want to delete it (or get the right OEM crank setup)

Installed to a Merc tech and was told the factory setup was the outdrive impeller and no through hull/crank pump.

Thanks, Tom

That should say ‘I talked to a Merc Tech…’

 

[DennisG01]

OK, good - that extra info helps clarify things.

Yes, the original install would have been WITHOUT the crank-mounted pump.

The crank mounted pump will absolutely supply more water than the in-drive pump. If anyone tells you differently, they are flat out wrong.

Now, whether you NEED the cank pump can only bet determined by getting a good load on the boat for an extended time. Running in neutral doesn't give the answer. It very well might be fine with the drive pump - but the question still remains... if everything is good with the drive pump, WHY would someone go to the expense of installing the crank pump?

 

[Tomtomterrific]

OK, good - that extra info helps clarify things.

Yes, the original install would have been WITHOUT the crank-mounted pump.

The crank mounted pump will absolutely supply more water than the in-drive pump. If anyone tells you differently, they are flat out wrong.

Now, whether you NEED the cank pump can only bet determined by getting a good load on the boat for an extended time. Running in neutral doesn't give the answer. It very well might be fine with the drive pump - but the question still remains... if everything is good with the drive pump, WHY would someone go to the expense of installing the crank pump?

Thanks!

OK, good - that extra info helps clarify things.

Yes, the original install would have been WITHOUT the crank-mounted pump.

The crank mounted pump will absolutely supply more water than the in-drive pump. If anyone tells you differently, they are flat out wrong.

Now, whether you NEED the cank pump can only bet determined by getting a good load on the boat for an extended time. Running in neutral doesn't give the answer. It very well might be fine with the drive pump - but the question still remains... if everything is good with the drive pump, WHY would someone go to the expense of installing the crank pump?

Thanks. I did run it for 30 mins under load with the seacock closed so I think the in drive impeller is ‘supplying’ enough water.

Idk when/why the crank pump was introduced. The PO told me it was repowered around 2000 (the motor's a 97) and it has a newer SEI outdrive.

Any recommendations on a good crank pump setup? I can run it as is with a good redundant supply. As I said I just don’t like the way it wobbles.

Thanks, Tom