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TimBSmith 07-17-2022 11:39 PM

Help with sudden RWC overheating diagnosis..
Sailing out of Salem, MA this afternoon / evening. Monitoring temperature and and exhaust as I always do. Flawless operations for weeks after my fuel system pressure issue.

-No thermostat. Diverter valve. Usual run closed.
-Raw water cooled.
-Rarely breaks out of 170/180.
-Water batches reliably, basket filter bubbles briskly.

This afternoon we found some nice wind and decided to turn off the motor.
When I went to check temperature (I had last checked maybe 30 minutes earlier). Temp had risen to 208+ F across all spots I check on head.

-I went into trouble shooting mode.
-Check basket, clear.
-Checked impeller, wet, intact and hot water leaking from backing plate when I removed to check impeller. (new impeller last year).
-Marine exhaust hose from water lift hot to the touch and maybe felt firmer than usual. (New last year).
-All hoses forward of the water pump were hot to the touch.
-Confirmed flow from inlet through hull to basket filter.
-Oil level full and no sign of water.
-Transmission case felt hot.

-Restarted engine, no choke needed, opened intake through hull, no noticeable water flow or bubbling through basket filter. No water leaving the external exhaust.
-Shut motor down.
-Closed feed.

Wind picked up, a blessing, we sailed back to mooring in 12 Knots, steady south westerly. Oasis sailed like a dream, thought we might need tow service, but NOT ON THIS DAY BABY!

Back on mooring. Tidied up regular post-sail procedure.
-Started engine one last time as test.
-Started first crank with choke (You go girl!)
-Opened feed.
-No joy on water pressure to basket filter.
-Did notice leakage from pump backing plate. (I may have reinstalled the thumb screws too loose or didn't seat the gasket flush (maybe screw cross thread.) Still love the thumb screws!

Tomorrow morning going back to the boat to resume diagnostics.

-I will search list for signs of a failing or failed water pump.
-What diagnostics would you offer as I check the cooling system end-to-end tomorrow? I don't have exhaust back pressure gauge.
-How do our pumps usually fail. Do they seize-up or do they simply slow down and create less pressure? What are symptoms of a failing or failed water pump? I vaguely remember reading about a weep hole, and oil leaks from accessory drive? Investigating. Welcome thoughts.

Thank you brain trust. Until next. Stay well.

Peter 07-18-2022 06:47 AM

Once while warming up at dock I noticed steam coming from exhaust and no water flow. Shut down and started to troubleshoot.

Went for easy to test first - is water coming in from thruhull? Nope. Turned out I had pulled a jelly fish into the thruhull.

It was surprisingly difficult to get it out of there. No amount of me blowing into the hose would clear it. Finally hooked bilge pump discharge up and after a few minutes of cycling on/off it cleared.

My reading of your post suggests that checking for water in from thruhull may be a useful place to start.

Good luck!


Dave Neptune 07-18-2022 09:24 AM

The engine is running way to hot. A raw water engine with no t-stat should have a hard time getting above 140. At the temps you are running the salts will come out of suspension and crystalize in the block reducing heat dissipation and reducing flow through the block.
A good way to keep track of the water pump performance is with a water pressure gage. I have used many on marine applications where the pump runs in dirty or muddy waters as the debris eats away the pump veins.
You probably have a clogged line and/or are sucking air into the pump where it leaks. Pull the intake line at the pump and check for good flow and clear it if necessary. If it is open there check the pump impeller as it is an easy fix. If you are still running hot once you confirm the pump is OK try closing the diverter some and if it still stays hot a flush is in your engines future.

The temp rise you observed is NORMAL. As the engine is cooled via the cold water the internals of the engine are much hotter so when you shut down that heat in the internals radiates to the water raising the temp as it is no longer being carried away. My RWC engine ran at around 140 at a hard cruise and I would always let it idle for a few minutes before shutting down. Then a about 5 minutes after shutting down I would hit the key and see how much the temp would rise, usually about 20 degrees.

David Neptune :cool:

Sam 07-18-2022 02:19 PM

I have a raw water cooled early model for 45 yrs - different cooling routing than late model but similar issues. Normal running temp is 140 with stoke thermostat. I like to start with simple solutions. Every few years I see the temp moves up to 160 - 180. We are in Lake Michigan so I do not need to worry about salt water issues.

I take a piece of foot length of fairly stiff 10=12 gauge solid core wire and start poking into pump outflow and any water passages that I have access to. In a pinch I have even carefully used a wire coat hanger. Gunk, rust. debris etc. has been cleared every time and issue solved.

Another point is that visual water flow can be deceptive. About 15 yrs ago the A4 was running hot. I unhooked the disharge hose to check flow and it looked great to me [no pressure gauge]. An older sea salt looked at it and said I needed a new water pump based on the visual pressure/flow - a different perspective. I knew the impellar was new so I changed out a 30yr pump - again problem solved.

TimBSmith 07-18-2022 03:34 PM

Update 1. Issue unresolved. Making progress.
Thank you for all the notes. Feed. Running hot. Salts. Flush. Normal heat gain. Reaming hoses and fittings. Testing flows of hose segments starting with feed. Roger.

Water pressure gauge in my future. I also read a lot into historical threads last night.

A couple hours with the cooling system today and one observation from trouble shooting yesterday. More work to be done.

Observation yesterday.
1) I recalled and meant to add that yesterday removing the basket filter top was significantly more difficult than normal. It (filter) was completely empty of water and felt as if under strong vacuum pressure when I finally removed the top there was a noticeable hiss as the vacuum cleared. So without jumping to conclusions or cutting diagnostic short, I started to think the feed had been block by something.

Observations and steps today.
1) I made a first attempt at reseating the backing plate to the water pump. And inspecting the water pump weep hole etc.
-The plate was not seated correctly yesterday, the round gasket was not set into its channel.
-Set the gasket and retightened plate with thump screws. Got this result. After startup.
Clearly have to go back in and reseat again and see if I can figure why thumb screw leaking (gasket did not look damaged). Wondering if the plate gets worn into a certain registration and if I don't get it right when replacing it might not seal well.
-There is no sign of weeping or seeping of oil or water at the pump seep hole. See video above.

2) Restart. There was water flow through basket and there was water batching and exiting the exhaust. The water pressure in the basket was anemic compared to all prior startups and historical observations. The basket was barely filling 1/2 way up. Head temp quickly raised to 150 to 170 within a few minutes of startup. Shut down.

3) Aside from the poorly sealing water pump backing plate, which is not helping pressure. Next trip to boat I will see about:
-Reseating (again) the pump plate.
-a method to try and flush out the feed, apply pressure and test flow at the feed through hull. I have a hose connector T'd in so maybe I will block the feed hose toward the strainer and plumb my backup bilge pump to it and a water source. First blow water out, then suck water in.
-a method to bring water source to pump intake without using strainer flow. Plumb around strainer and feed to see if batching flow increased.
-methods for clearing hoses and choke points. Hanger etc.
(I replaced all of the hoses to the waterjacket inlet and the diverter valve to thermostat in the off season. Replaced hoses had zero build up. Though that, I know, is only part of the bracketing.
-main choke points with hose access are water jacket injector, L at the thermostat housing, then the manifold fitting. Others?
-consider other flush options while on my mooring.

I will update when I have more done. Please continue insights and guidance will adjust as I work from feed to manifold. Until next. Stay well.

Dave Neptune 07-18-2022 04:39 PM

The loose plate will really kill water flow under any kind of pressure as it sucks in air. The plate needs to be "flat" and the "0" ring must be seated. If any air is getting sucked in anywhere the system will not function well.

Also take a good look at the impeller as running dry will damage it quickly.

Check for a restriction at the exit fitting on the manifold sa it can gather krap and restrict flow.

Dave Neptune :cool:

joe_db 07-18-2022 07:33 PM

I am RWC with a bypass valve and I can hardly crack 140 with the bypass in the hot position, let alone cold!
As for no water at all, the water pump impeller can come apart and block the pump totally. I have also had a little fish get sucked into the pump and plug it.

Easy Rider 07-19-2022 12:36 AM

I recalled and meant to add that yesterday removing the basket filter top was significantly more difficult than normal. It (filter) was completely empty of water and felt as if under strong vacuum pressure when I finally removed the top there was a noticeable hiss as the

My thoughts would be that the pump is trying to suck but there is a restriction between the through-hull and the basket filter causing the vacuum in the basket when you removed the basket lid. 1. Basket lid hard to remove. 2. Felt like a vacuum. 3. Hissing noise removing the lid.
Start at the through-hull and work upstream checking for restrictions or air leaks. Good Luck.

Surcouf 07-19-2022 03:54 AM


Originally Posted by Easy Rider (Post 128825)
Start at the through-hull and work upstream checking for restrictions or air leaks. Good Luck.

a good blow of compressed air backward from the basket suction line may help push back outside anything that could be blocking your water intake...

TimBSmith 07-21-2022 10:08 PM

Headed to boat tomorrow for day of trouble shooting...
Quick question.

Does anyone know if the Moyer flange pump, which my PO installed, uses both of the O rings that come with it? I recall when I started trouble-shooting this overheating event that I found one O ring loose and re-seated it in the groove on the pump back. I did not see a second O ring loose.

Maybe it sits below the one I found and reseated?

One course of business tomorrow is to reconfirm impeller condition and account for all of the O rings I am supposed to have with the flange pump. If one is missing, that may help explain my leaky plate.


I am also going to attack the raw water through hull with available means to flush anything out that may be stuck in there. And see to a couple of possible choke points.

Until next. Stay well. Advice on O rings appreciates soonest and I will search the threads.

TimBSmith 07-21-2022 10:22 PM

Reference document for MMI flange pump maintenance..

TimBSmith 07-22-2022 05:30 PM

Update from 7/22 trouble shooting. Success!
Half a day at the boat in 98 F heat. Most of the time in the port quarterberth and the starboard "sail locker". Lost a few pounds of water weight for sure.

Raw Water Feed Through Hull Investigation
-Removed hose after a cautious wrestling match. (Images of a sheered Marelon through hull flash in my mind.) Hose removed. A viscous clear fluid seeped out of closed through hull along with a slight smell. Probed and flushed through hull both directions. Flow was strong/symmetrical when valve opened. Had never done this before. The pressure was impressive.

-Inspected hose between through hull and garden hose T fitting.
A plug of kelp like material was found to be stubbornly set between the through hull side and the garden hose T fitting.
-Material wedged along the radius of the forward edge of the garden hose T fitting inside the feed hose.
-The kelp came out in the shape of a dense sewing thimble. More viscous fluid along with the plug.

Here is the picking tool I used inside the section of the feed hose I am referring to. The material was woven and wedged in tight.

Here is the plug after unweaving the material.

Checked flow from garden "T" to basket filter. Basket filter to pump.

Moyer Flange Pump and Backing Plate Leak
-Much closer inspection of impeller. No signs of cracked or compromised paddles. Replaced last July. Clear that the impeller had never run completely dry. No dry wear around top nub of paddle. No noticeable play with impeller shaft.
-Much closer inspection of backing plate
Noticed radial etching on backing plate. I theorize that at some point in all this fine metal particles may have settled back between backing plate and paddles from the hose feeding the water jacket injector.

Cleaned out O ring seating groove. (confirmed no missing O ring/determined only 1 O ring used in groove).
-Marine grease in groove and on O ring. Noticed and noted a fine small flat spot on the O ring. Replaced backing plate.
-Tested cooling system. SUCCESS
-Spot checked water flow and temperature nominal relative to my history with the motor.

Checked for backing plate leak. Lead slower but still present. Same location. Leak greatly reduced yet there is still a droplet that slowly puddles.
-Will check backing plate housing and order new O rings. See if that stops it. Confirm that backing plate lays flat, no warping or bend.
Leak during running

Noted that leak when not pumping has slowed to point that no water drop pooled for at least 30 minutes after shutdown.

Choke Points and Flush
-Will still make my way around engine cooling choke points. And consider acid flush this season.

-Backing plate leak.
-Pump flushing/maintenance if metal particles making way into housing.
-Concerns about Garden "T" fouling feed before strainer.
-Temperature sender and gauge repair replace.
-Look into early warning systems available.
-Water pressure, exhaust pressure, etc.
-Fresh water cooling in my future.

Thank you for all the help this far. Welcome any suggestions on pump backing plate beyond my next steps. Very productive day because of this forum, MMI flange pump documentation, and the service, rebuild, and newsletter manuals.

W2ET 07-22-2022 07:07 PM

It is amazing how much water flows out of a relatively small hole not all that far below the water line.


TimBSmith 07-23-2022 07:40 PM

Update: Great family afternoon out sailng in a light breeze. Temp nominal.
-Temperatures under constant load 3.5 to 4.5 knots for 1 hour motor out; stayed in nominal range. Today that meant rarely above 150 F.

Motor seems to be running cooler than before the kelp blockage. Maybe some other pressure points released during the over heating pressure and event? Too early to tell.

-Maybe 3/4 drops from plate during entire motoring time in and out of gear about 2 hours. No noticeable leak after engine shutdown.

-Thank you Ken at MMI for callback on O rings. And I ordered replacements today.

-Thank you all for helping me come this far. More work to be done from this episode. And great to be back on the water.

Until next. Fair winds.

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