Sea Water Pumping Issue (25k in so far)

AZ_Brad_320

AZ_Brad_320

New Member
Oct 5, 2022
8
Boat Info
2007 320DA 350 V's
Engines
350 MAG V-Drives
I've read every thread on this subject and have gone down almost every road I can think of. I would APPRECIATE any advice as I'm 25k in and no boat to use. Here's the story.. 2007 320 Dancer with 350 V drives closed cooling system....had a sea water (exhaust) issue where port not pumping as much water as starboard day I bought it.

Here's what I've had done by Hales' Marine here in Phoenix:
  1. Replaced seacock..thought it might have been stuck
  2. Replaced exhaust manifolds and risers, preventative... figure she had seen salt water before and it was good money spent.
  3. Replaced sea water pump and pulleys
  4. New hoses from strainer to pump etc.
They gave me the boat back dipped it and ...same problem (not enough water pumping so low pressure on Vesselview) alarms and shuts motor down.
  • At mechanics suggestion replaced tranny coolers....back in water same problem.
  • At mechanics suggestion replaced heat exchanger...back in water same problem
  • They have put 2 different water pumps on it (mercruiser brass) and ...same problem
We have jumped the water pressure sensor over to the starboard motor just to see if it was a sensor thing...no luck.

What the hell could this be? Has anyone ever heard of anything like this?
  • It presents itself as a water pumping issue (not enough volume of water being pumped through manifold), port running 30 degrees hotter than starboard.
  • So water pump seems like the best place to start but after 2 new ones its same old same old.
  • Blockage could be a thing if we hadn't replaced everything on the cooling system.
  • I've asked about a collapsed hose and they swear we replace all the hoses.
  • Is there anyway they messed something up with the manifold/riser job? A gasket slipped off in there or something.
  • Thought about air leakage but they swear they did the clear hose test?
 
Ok, stop throwing parts at the problem and start tracking the water.
Remove the strainer basket and slowly open the seacock, it should fill and flow. Slow fill, go to the scupper under the boat and see if it’s blocked. Back flow, but it could be fouled. Ok next, go to the raw water pump. Was it run without water after replacement? If so the impeller is shot. Replace it. If not trace the output line to the lower heat exchanger. Mine is down low on the forward part of the engine. That’s were most impeller bits get stuck and block the flow. Needle nose pliers to get the big parts and then back flush the exchanger.

Last thing, you could have split tubes in the exchangers or blocked tubes. That would mean pulling the exchangers and cleaning them professionally. Start with the main upper exchanger.

I wish you luck and let us know how it goes. All of these things you can do.
 
I remember a post not to long ago guy had a similar issue and he soaked his t stat housing in muriatic acid and water and fixed it.
 
Gentlemen.....he has a water flow issue which is causing the engine to alarm and heat up. The thermostat on the closed cooling side would not trigger a water flow sensor.

Since we don't know the history of the boat prior to the OP....the best way to figure out is to do some simple tests. First start with how much water is coming out of each exhaust port (assuming you have side exhausts) per minute at 1,000 rpm. You can use a gallon jug and a watch to get a pretty good estimate.

Empirically, that gives you a hard baseline of the problem you are chasing. Let's say the test shows he has 5 gallons a minute on the starboard side and 2.5 gallons a minute on the port.

The port pump, strainer and connecting hose is new so a blockage there is unlikely.

From there you have to follow the hose from the pump to the manifolds, heat exchangers and coolers. My speculation is that an impeller let loose previously and a few vanes are blocking the water flow. Pump pressure is probably fine but the blockage is impeding the water flow. No easy way to do it......you have to pull each hose and visually check it and what it connects to. Usually the vanes lodge themselves where the hose turns or where it connects to something.

Your note says they replaced all the cooling hoses but they missed something. I did make a tool a while back that may help you sort it out. I used a low pressure gauge and pvc fittings to measure water pressure at several key points. Specifically the water pressure going into the manifolds, risers, heat exchangers and coolers. The pressure tells you pretty quickly where the problem is.

gensentry.jpg


Pressure on the other side of a blockage is less than it is in front of it. Checking a few key points will find the issue.

BTW Welcome to CSR!
 
I agree 100% with what has been told to you about tracing and testing the flow of water through your engine. But, why the heck isn't your "mechanic" doing this? This issue is "boat mechanic 101". Instead it looks like he's just listening to you tell him to replace things and I'm pretty sure he's having steak and lobster for dinner.....just sayin'
 
What lake do you boat in
 
dwna1a said:
Ok, stop throwing parts at the problem and start tracking the water.
Remove the strainer basket and slowly open the seacock, it should fill and flow. Slow fill, go to the scupper under the boat and see if it’s blocked. Back flow, but it could be fouled. Ok next, go to the raw water pump. Was it run without water after replacement? If so the impeller is shot. Replace it. If not trace the output line to the lower heat exchanger. Mine is down low on the forward part of the engine. That’s were most impeller bits get stuck and block the flow. Needle nose pliers to get the big parts and then back flush the exchanger.

Last thing, you could have split tubes in the exchangers or blocked tubes. That would mean pulling the exchangers and cleaning them professionally. Start with the main upper exchanger.

I wish you luck and let us know how it goes. All of these things you can do.
Click to expand...
 
Thanks a bunch for the input!

Strainer check is all good (water flows into boat when lid is opened) this was an issue before, we moved the strainer down in the hull a bit) We put a new sea cock as well in so that's all good as well.

New heat exhanger via Mr. Cool so that's good.

My gut is that this is a impellor vane somewhere in the mix, I'm going to take this intel to my mechanics today! To get them started chasing possible clog points.
 
PlayDate said:
Gentlemen.....he has a water flow issue which is causing the engine to alarm and heat up. The thermostat on the closed cooling side would not trigger a water flow sensor.

Since we don't know the history of the boat prior to the OP....the best way to figure out is to do some simple tests. First start with how much water is coming out of each exhaust port (assuming you have side exhausts) per minute at 1,000 rpm. You can use a gallon jug and a watch to get a pretty good estimate.

Empirically, that gives you a hard baseline of the problem you are chasing. Let's say the test shows he has 5 gallons a minute on the starboard side and 2.5 gallons a minute on the port.

The port pump, strainer and connecting hose is new so a blockage there is unlikely.

From there you have to follow the hose from the pump to the manifolds, heat exchangers and coolers. My speculation is that an impeller let loose previously and a few vanes are blocking the water flow. Pump pressure is probably fine but the blockage is impeding the water flow. No easy way to do it......you have to pull each hose and visually check it and what it connects to. Usually the vanes lodge themselves where the hose turns or where it connects to something.

Your note says they replaced all the cooling hoses but they missed something. I did make a tool a while back that may help you sort it out. I used a low pressure gauge and pvc fittings to measure water pressure at several key points. Specifically the water pressure going into the manifolds, risers, heat exchangers and coolers. The pressure tells you pretty quickly where the problem is.

View attachment 146329

Pressure on the other side of a blockage is less than it is in front of it. Checking a few key points will find the issue.

BTW Welcome to CSR!
Click to expand...
 
Great advice.... You are correct in the volume of water at the exhaust port is much weaker on the port motor. My first write up to them identified this. (I think we were getting 1.5 PSI port vs. 6-7PSI starboard on the water pressure reading) After 2 new water pumps same thing...uuuuggghhh Love the pressure gauge solution I'm going with this one to the mechanics. It's funny these are "the guys" in town for the bigger boats, but this problem has been kicking there ass for 6 months. So now I turn to the A team for some intellectual insight. Thank you for your time...this is exactly what I was hoping for with this forum! Stay tuned.
 
brewster16 said:
I agree 100% with what has been told to you about tracing and testing the flow of water through your engine. But, why the heck isn't your "mechanic" doing this? This issue is "boat mechanic 101". Instead it looks like he's just listening to you tell him to replace things and I'm pretty sure he's having steak and lobster for dinner.....just sayin'
Click to expand...
 
They told me out of 65 work orders "I was the only problem child" I'm 25k in but for some other stuff as well. (I thought I was going in for a 2k repair haha) It's funny I have been thinking this entire time that "they are the experts" and "they know what they are doing"....I see here in this forum that most owners have a figure it out myself mentality. But when it comes to the exhaust manifolds/riser/pumps/pulleys etc...that was just more then daddy was willing to commit to..haha ..especially in the 320 with v-drives...tight as hell down there!
 
Logically, if both the water pressure and the exhaust flow is low it's NOT likely a blockage between the water pressure sensor and exhaust port. If there were a blockage in that area it would cause an increase in pressure with the new pump with it trying to force more raw water through the system.

That leaves some kind of blockage from the water under the boat to the water pressure sensor. Lack of sufficient water feeding the pump would be my guess (since the pump is new - not just the impeller).

You said the water flow from the strainer was ok, but did you compare it to the other engine's strainer?

Where is your water sensor located? From data online, it appears to be on the back end of the raw water pump. If that's the case, it narrows down the search of restrictions from the water under the boat to the water pump itself.

Just for sh#ts and giggles, you might confirm the flow by removing the raw water feed hose from the heat exchanger, fire up the engine for a few seconds and fill a bucket with that water. Repeat for the good engine and compare.

That's my 2 cents!
 
It is a simple problem to diagnose using a home made pressure gauge. Start with the hose running to the heat exchanger from the Sea Water pump. The "in" port should read pump pressure at 1,000 rpm around 8-10 psi. Then check the "out" port and it should read 8-10 psi. Follow the hoses to the oil cooler and exhaust manifolds and repeat the process. Within 30 minutes ......you will have your answer where the problem is.


Keep in mind where the Smartcraft raw water pressure sensor is located. The restriction is before the sensor.
 
It seems you have an air leak on the suction side of things. Happened on my boat. Ended up being hammer dings on the pump body where the impeller cover gets installed. The service guy tried to beat the impeller onto the pump. Took me weeks to figure that out.
 
On the side with low water pressure -- have you verified this low reading with some method other than the gauge/sensor? I can't remember if you said you swapped sensors from one side to the other to rule that out as the problem.
 
ttmott said:
It seems you have an air leak on the suction side of things. Happened on my boat. Ended up being hammer dings on the pump body where the impeller cover gets installed. The service guy tried to beat the impeller onto the pump. Took me weeks to figure that out.
Click to expand...

Allegedly ......the "mechanics" already tried using a clear piece of hose to determine if there was an air leak. That said.....in my book.....an air leak is still on the table. Until they actually test the pressure and follow it.....they will keep throwing parts at it.

I suppose this is as good a time as any to ask the OP at what point did this problem show up and what work was done prior to that moment?
 
PlayDate said:
Allegedly ......the "mechanics" already tried using a clear piece of hose to determine if there was an air leak. That said.....in my book.....an air leak is still on the table. Until they actually test the pressure and follow it.....they will keep throwing parts at it.

I suppose this is as good a time as any to ask the OP at what point did this problem show up and what work was done prior to that moment?
Click to expand...
It doesn't take much of an air leak at all to render a pump useless. Bubbles may be very tiny in a clear tube. Low water pressure indicates suction issues or something with the impeller or what drives the impeller.
The issue I had with my boat was insidious; At static and low engine RPM water flow was normal. There was enough (NPSH) net pump suction head (the pump is slightly below the water level) to enable the pump to appear it was operating correctly. However, what we found as engine RPM increased the discharge water pressure went down dramatically. As it ended up when the NPSH went negative that tiny air leak came into the picture and the pump flow rate went down. Hard to see but a tiny hammer ding across the cover plate o-ring groove.
IMG_2556.JPG
 
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