• On September 1st, Maine Sail suffered a major hemorrhagic stroke. One of the most generous members of our sailing community, he has helped thousands. Now it's our turn. Click here to learn more

Hen's Teeth: The Saga Continues.....

Jan 19, 2010
950
Catalina 34 Casco Bay
Brief recap: Had started to notice a gradual overheating over a period of time.. First thought was that the impeller was failing. After replacing the impeller, there was an inability to get water to come out of the stern discharge. Replacing the cam did help, but lost the prime yesterday. Today: Removed the pump cap and lubed the impeller. Removed the thru hull seen line at the pump to prime, but it had water in it. Started the engine and was rewarded with discharge water..
Facts: 1986 Universal M25
Oberdorfer pump ( OEM?)
Heat exchanger caps dropped and clear sightline to port side
First new impeller failed, second holding strong
New cam installed
New intake hose and pump to exchanger installed
Oberdorfer pumps currently unavailable
Boat is propelled by an 3 bladed Autoprop
WOT yields 3000 RPM when not in gear
Normally the engine in forward WOT will only yield 2300 RPM and push the boat at 6.8 to 7.2 kts
NOW: Above 1900 RPM overheating will slowly start
1500 RPM yields 5.2 to 5.4 KTS
1900 RPM yields 5.8 to 6.2 Kts

CONCLUSIONS: Yesterday when the engine was hot and had lost the prime after checking the strainer and would not pump it was reasoned that the heat expansion of the pump body that is already believed to be out of tolerances that were exacerbated by the heat of the pump.
Today with a cold engine and no need to prime, the engine/pump was able to draw, pump and cool the engine. The replacement of the cam added significant area to the internal pump body that allowed it to perform. BUT, that alone is not enough when the engine is under load.

So for now, RPMs will be held below 2000 RPM...

Once Oberdorfer is back up and in production, a new pump will be acquired and installed. This might not happen until next spring, but an update will be provided.
 

capta

.
Jun 4, 2009
4,306
Pearson 530 Admiralty Bay, Bequia SVG
We use the same pump on our Onan genset. Is there much wear on the inside of the impeller cover plate? If so, this could be a part of your problem. How is the exhaust water output? Near normal? Have you put a plain hose on the discharge (out) side of the pump and seen how much water it puts out? Do you have another thru hull you could use as an intake to test the input flow?
If all is OK on the seawater side look to the fresh water side. Have you tested the thermostat? If it isn't opening all the way this could also be some of the problem. If your engine is a Kubota conversion, which I suspect it is, then the fresh water circulation pump is aluminum on a cast iron block. That pump could be the problem. Just some other thoughts.
 
  • Like
Likes: sailme88
Nov 6, 2006
9,225
Hunter 34 Mandeville Louisiana
Had a problem like that on a friend's C-34.. The new impeller was not as wide as the original by about a 32nd of an inch.. Replaced with correct impeller and all was fine..
 
Jan 19, 2010
950
Catalina 34 Casco Bay
Had a problem like that on a friend's C-34.. The new impeller was not as wide as the original by about a 32nd of an inch.. Replaced with correct impeller and all was fine..
Impellers are Catalina Direct. They get them from Westerbeke... yet there have been problems
 

DougM

.
Jul 24, 2005
2,181
Beneteau 323 Manistee, MI
There was a problem some time ago with Globe impellers somewhat related. It seems that the bond between the impeller material and the metal core would become detached. The pump shaft would turn along with the core of the impeller while the blades would not.

Also, have you checked the intercooler for old bits and pieces of impeller clogging the system, and that the engine thermostat is functioning properly?
 
Jan 19, 2010
950
Catalina 34 Casco Bay
There was a problem some time ago with Globe impellers somewhat related. It seems that the bond between the impeller material and the metal core would become detached. The pump shaft would turn along with the core of the impeller while the blades would not.

Also, have you checked the intercooler for old bits and pieces of impeller clogging the system, and that the engine thermostat is functioning properly?
Doug, None of the impellers have shown any loss of structure that would contribute to a clogging of the exchanger. Having said that, one of the first places that I checked was the exchanger. Both caps were dropped and the tubes were clear. One of the new impellers that Westerbeke supplied to a vendor displayed the above Globe problem. Now awaiting the vendor to make good.
 
Sep 30, 2016
302
Hunter 23.5 Patoka Lake, IN
Like Capta mentioned, Id try a new thermostat. They go bad, and they are cheap. Dont forget to get a gasket.
 
Jan 19, 2010
950
Catalina 34 Casco Bay
Like Capta mentioned, Id try a new thermostat. They go bad, and they are cheap. Dont forget to get a gasket.
The thermostat may indeed need replacing, but it can't and won't work properly is there is no water across the exchanger and out the transom....
 

jviss

.
Feb 5, 2004
4,627
Tartan 3800 Westport, MA
The thermostat may indeed need replacing, but it can't and won't work properly is there is no water across the exchanger and out the transom....
So, you are convinced that the root cause is that the sea water pump does not move enough water when it's hot, true?

I have a hard time buying into this, since the sea water pump is cooled by a continuous flow of sea water through it.

Have you made any temperature measurements?
 

RoyS

.
Jun 3, 2012
1,210
Hunter 33 Steamboat Wharf, Hull, MA
You appear to have two problems:
1. You should not be reaching hull speed at low engine rpm's; you are over-propped.
2. You have a cooling water flow problem, most likely an obstruction in the thruhull.
 
Jan 19, 2010
950
Catalina 34 Casco Bay
So, you are convinced that the root cause is that the sea water pump does not move enough water when it's hot, true?

I have a hard time buying into this, since the sea water pump is cooled by a continuous flow of sea water through it.

Have you made any temperature measurements?
I am convinced that the 34 yrs of spinning impellers have eroded the internal pump walls to the point that the vanes are making less than good contact. My QED for this is the replacement of the cam. Before the new cam zero water.. immediately after the replacement... water. If I let the prime drop by checking the strainer when the engine is hot, it will NOT draw water. Same process on a cold engine... water
 

jviss

.
Feb 5, 2004
4,627
Tartan 3800 Westport, MA
If I let the prime drop by checking the strainer when the engine is hot, it will NOT draw water. Same process on a cold engine... water
While the temperature is coincidental with the observation, we don't know if it's causal. They are other factors. Have you observed no flow through the pump in the latter case, by checking for flow or pressure at the pump outlet, or are you basing this on observing no water out the exhaust?

I find it hard to believe that there could be such a binary result from a small change in temp. Maybe I will learn something here.

I forget, did you mention the condition of the inside of the pump front cover?

(I forgot, I was going to measure the temp of my water pump this weekend!)

Is there anything else that could prevent flow when the engine's hot?
 
Jan 19, 2010
950
Catalina 34 Casco Bay
While the temperature is coincidental with the observation, we don't know if it's causal. They are other factors. Have you observed no flow through the pump in the latter case, by checking for flow or pressure at the pump outlet, or are you basing this on observing no water out the exhaust?

I find it hard to believe that there could be such a binary result from a small change in temp. Maybe I will learn something here.

I forget, did you mention the condition of the inside of the pump front cover?

(I forgot, I was going to measure the temp of my water pump this weekend!)

Is there anything else that could prevent flow when the engine's hot?
So I removed the thermostat yesterday and then went for a test run. At the firewall a slight increase in temp before pulling back the RPMs to 2000. With the reduction in RPMs the temp dropped quickly. Today, at idle maybe 120 with water flow. Motored into the harbor for a sail. AS long as RPMs were below 2K temp stayed around 130-140. Shut down for maybe 10-15 minutes. Upon restarting no exhaust water.

So, QED'd the thermostat

Cold engine yields water and as long as it stays running...water exhaust. Shut down while engine and pump housing hot or warm... zero exhaust water. It would appear that the tolerances with in the pump body have worn. When cold and contracted a tight enough seal to pump. Shut down warm or hot and the prime slips by and no water is pumped.
 

jviss

.
Feb 5, 2004
4,627
Tartan 3800 Westport, MA
(That's an odd way of using the abbreviation "QED," which, in my science education was used to mean "that which was to be proven," and literally means "quod erat demonstrandum," or "which was to be demonstrated." Is that what you mean by this? What was it that you demonstrated with this trial run? That the thermostat is not the issue?)

I'm not being a troll, I just find it so odd that a pump would click over to zero water from pumping due to a change in temperature, to the point that it loses prime and then cannot re-prime. I would expect only a degradation in pump performance. Flexible vane pumps are self priming. How could the dimensions of the inside of this pump change so much from temperature to render it completely useless?

What does the inside of the cover plate look like?

What else could fail in some dramatic way from elevated temperature and heal itself when it cools? Maybe a hose, where the inside wall is collapsing, like an arterial dissection (see the second pic):



Have you verified that a loss of prime is what's causing the lack of flow?

Have you replaced all the raw water hoses?

I guess I'll have to buy our theory on the pump, and wait and see.
 
Last edited:
Jan 19, 2010
950
Catalina 34 Casco Bay
(That's an odd way of using the abbreviation "QED," which, in my science education was used to mean "that which was to be proven," and literally means "quod erat demonstrandum," or "which was to be demonstrated." Is that what you mean by this? What was it that you demonstrated with this trial run? That the thermostat is not the issue?)

I'm not being a troll, I just find it so odd that a pump would click over to zero water from pumping due to a change in temperature, to the point that it loses prime and then cannot re-prime. I would expect only a degradation in pump performance. Flexible vane pumps are self priming. How could the dimensions of the inside of this pump change so much from temperature to render it completely useless?

What does the inside of the cover plate look like?

What else could fail in some dramatic way from elevated temperature and heal itself when it cools? Maybe a hose, where the inside wall is collapsing, like an arterial dissection (see the second pic):



Have you verified that a loss of prime is what's causing the lack of flow?

Have you replaced all the raw water hoses?

I guess I'll have to buy our theory on the pump, and wait and see.
Yes, ALL hoses have been replaced. QED does refer to to the thermostat.

My theory on the heating/ loss of prime is that the interior walls of the pump have gradually been worn away. With old cam in place there was not water movement in any condition. With the new cam, water would pump with a cold engine and continue as long as the pump ran. Once shut down, a restart while the engine was still hot would not render any water. Let the engine go cold....water. Now If I could get my hands on a new Oberdorfer....
 

jviss

.
Feb 5, 2004
4,627
Tartan 3800 Westport, MA
Yes, ALL hoses have been replaced. QED does refer to to the thermostat.

My theory on the heating/ loss of prime is that the interior walls of the pump have gradually been worn away. With old cam in place there was not water movement in any condition. With the new cam, water would pump with a cold engine and continue as long as the pump ran. Once shut down, a restart while the engine was still hot would not render any water. Let the engine go cold....water. Now If I could get my hands on a new Oberdorfer....
I have the original pump from my M25, from before the upgraded pump was installed, it that's of any interest. It make have a leaky seal.
 
Jan 19, 2010
950
Catalina 34 Casco Bay
I have the original pump from my M25, from before the upgraded pump was installed, it that's of any interest. It make have a leaky seal.
'Preciate the offer.. At this stage of the game I need to stop chasing my tail and replace all of the possible issues with new items that offer a seasonable chance of success. I must admit the frustration is beginning to take hold. Thought about replacing the aqua lift muffler... a multi month back order has quashed that. New hose from exchanger to exhaust mixer today. Nipple at mixer inspected and rodded... If I can't locate a new pump in a timely fashion I may need to bypass pump. Remove the impeller from the Oberdorfer and move the hoses to an electric pump of some kind, i.e. wash down pump etc...