Raw water pump - Ouch!

[Compass790]

Originally Posted by jimbunyard

Some might say I live a sheltered life, but I've never seen a flexible rubber impeller water pump">raw water pump with a ceramic/graphite pressure seal, though such seals are the norm for freshwater/engine coolant circulation pumps as well as other centrifugal pumps like water or well or pool pumps.

As for "there is no possibility of water getting into the oil", standard rubber lip seals generally only work one way; they can and sometimes do allow contaminants, for a variety of sometimes subtle dynamic reasons, to enter a system into which they are 'sealing' another substance.

Perhaps I'm "overthinking" it Jim but doesn't item 7 in his view resemble a mechanical seal? I too haven't seen one but I'm not a fulltime marine mechanic.

[Compass790]

Originally Posted by lituya1617

I beg to differ. I was a commercial fisherman with a wooden boat for many years. The nonsense about raw water cooled heat exchanger and water-cooled exhausts is just that, nonsense. If you have a "yachty" mentality, you may buy the nonsense but no commercial fisherman wants to risk his life and income to the possibility of a weed-choked water intake, a broken v-belt, a spun keyway, a broken or burned impeller made of rubber, a salted exhaust water injector, a ruptured hose that will sink you quickly, or a leaking/plugged heat exchanger. Pumping a continuous large volume of salt water into a boat is dumb! Many pleasure yachts have sunk because of this application. Hoses break, boats sink. Not good. A keel cooler heat exchanger is a no-moving-parts simple system fastened to the hull in the protected garboard-keel angle. It has minimal drag, less than the propeller shaft and strut, and contains antifreeze and water with anti-rust compounds to protect the engine. The engine water pump is the only pump used - and it is used with internal heat exchangers too. Such pumps are highly reliable and easily repaired. You are required to have a water-cooled exhaust on a boat with an enclosed engine room; therefore, your engine has an exhaust header that is water cooled. However, from the header to the outside air, the exhaust pipe is simply insulated with fiberglass and placed inside a metal heat shield to prevent skin burns. An efficient and cheap automotive muffler can make the exhaust nearly inaudible. The heat shield also functions as a passive cooling vent for the engine room. Having the exhaust go straight up allows one to hear the function of the engine and look for signs of problems like smoke or weird noises - things a water lift muffler prevent. But the worst thing about the water-cooled and water injected exhaust systems so common on sailboats and yachts is the fact that the exhaust valves and cylinders are exposed to salt water vapors when the engine is not running. Think about this: your open steel exhaust valves and the iron heads and steel rings in the cylinders directly communicate with a large volume of warm salt water when you shut down the engine. When the engine cools, the air in the exhaust shrinks and draws the water even closer to the block. Over time, a matter of only a few months, you can rust up you engine to the point it needs a complete overhaul - just because you "like" a water-cooled exhaust. Not a wise choice. Sure, you can flush the system with fresh water but even that is not good for the internal parts of your engine. My opinion: keel coolers are by far the best option.

Yes agree with a lot of your well argued points but I've heard too many stinking fish boats coming from a long way off to be convinced about the noise factor. To address keel cooling pipe drag,yachts are designed to avoid drag, who wants more wetted area?
Good point about salt air, now I feel almost happy I have a single so I can shut it out by putting on compression stroke. ( wish I had a triple tho ) But your arguments are valid for someone who has a diesel hammering away 24/7.
Some actually enjoy it.

[donradcliffe]

A similar problem on a much larger scale. At least you didn't plug the weep hole.

https://www.sandiegouniontribune.com...110-story.html

[jimbunyard]

Originally Posted by Compass790

Perhaps I'm "overthinking" it Jim but doesn't item 7 in his view resemble a mechanical seal? I too haven't seen one but I'm not a fulltime marine mechanic.

Guess I do live a sheltered life, cause that's exactly what it is.

Given the care needed in installing such seals, I wonder if it's selection and installation in such an application was the ultimate cause in the bearing failure?

Sometimes simpler is better.

[Compass790]

Originally Posted by Wotname

I can't speak for your engine (don't know what it is) but many direct driven raw water pumps are simply tang driven off the end of the camshaft i.e. runs at half the crank rpm.

However it seems to me that many of you are overthinking the problem. The OP identified the root cause in the first post. Lack of timely maintenance!

A slowly developing leak in the raw water pump gives plenty of warning - that is what the slinger and weep hole is for. The design of these water pumps is quite satisfactory. Attend to to initial problem and the rest won't cascade into a serious problem.

Thanks to Reefmagnet for highlighting the real problem - it is a timely reminder for the rest of us. :Thank:

Jamhass hit the nail on the head back in post #16

Yes fair point Wottie but I prefer my systems to be idiot proof as many times I've proven to be one!
Still prefer to give the salt water fewer paths to get into the oil.

[Reefmagnet]

Yep, I was a nincompoop for letting the pump leak for so long without attending too it. I'm still cussing myself out about it!


Having said that, I'm still convinced that there is an issue with lubrication reaching the oil seal when the engine is lightly or irregularly used on this particular configuration. As we're about to head off on along term cruise soon, this probably will no longer be a factor moving forward. I'd certainly be one to preach from now on that if the water seal is leaking on the pump, the chance is high that the oil seal won't be far behind.



On a brighter note, I've got most stuff apart and the engine parts except for the bearing immediately facing the pump are servicable (although I'll replace the opposite side bearing while at it). I've got the final and most challenging task left to remove the remains of the outer bearing shells and a spacer from inside the pump body. Of course they're all pressed together as one and pushed down onto the oil seal flange so it's impossible to press them out or get anything behind them. Looking for ideas on how to proceed with they're removal?

[botanybay]

Originally Posted by Reefmagnet

My raw water pump had a small leak for a while. After a long layup the leak got a bit worse when relaunched, and water started appearing in the oil. Ripped the pump off the engine and the image shows what was underneath

The lesson learnt is replace that leaky water pump seal ASAP. Don't assume the oil seal is still fine.

Unfortunately the oil seal is there to keep oil in, not raw water out.

If the weep hole plugs it will result in alot of raw water in the lobe oil.

Interestingly, I do an oil analysis on every oil change (probably excessive but for $25 why not) and the salt content of the oil climbs dramatically at the first sign of the raw water seal failing. Long before excess moisture is detected in the oil.

I carry a spare, rebuilt and ready pump. 15 to 30 min job to swap pumps and then send leaking pump to shop.

Good luck with repair.

[Compass790]

On a brighter note, I've got most stuff apart and the engine parts except for the bearing immediately facing the pump are servicable (although I'll replace the opposite side bearing while at it). I've got the final and most challenging task left to remove the remains of the outer bearing shells and a spacer from inside the pump body. Of course they're all pressed together as one and pushed down onto the oil seal flange so it's impossible to press them out or get anything behind them. Looking for ideas on how to proceed with they're removal?[/QUOTE]

Well I'd try heating the pump body & freezing spray on the shells. Sounds like a right bstd of a job. You may have to use a dremel type tool otherwise or mount pump body in lathe & bore them out if you can machine/have access to lathe.

[Compass790]

Originally Posted by botanybay

Unfortunately the oil seal is there to keep oil in, not raw water out.

If the weep hole plugs it will result in alot of raw water in the lobe oil.

Interestingly, I do an oil analysis on every oil change (probably excessive but for $25 why not) and the salt content of the oil climbs dramatically at the first sign of the raw water seal failing. Long before excess moisture is detected in the oil.

I carry a spare, rebuilt and ready pump. 15 to 30 min job to swap pumps and then send leaking pump to shop.

Good luck with repair.

Does the water come out of the pumps weephole before it shows up on the oil analysis. I'm curious about that unstated part.
Very interesting that the salt content shows up before oil turns milky. But unsurprising that the analysis is much better than eyeball.
What engine model do you have?
Good idea to carry spare pump as you do

[lituya1617]

The lack of critical replies to my dissing of heat exchanger/salt water exhaust injectors would seem to reveal that my opinion carried the day. Or, people could just ignore me...

[Simi 60]

Originally Posted by Scorpius

I really don't know why the vast majority of pleasure boats use heat exchangers (with their associated salt water pumps) for engine cooling. Reading this forum, and from many other sources, they seem to be nothing but trouble. Around here there are a great many fishboats and small tugs in the same size range as your average sailboat these days and I can't say I've ever seen one of them with a heat exchanger setup. They all, like Scorpius, use keel coolers. Just run some kind of pipe along the outside of the hull, run the freshwater engine coolant through it, and Bob's your uncle: simple and keeps salt water WELL away from the engine - which has to be a good thing.

Mate has a similar sized vessel to us with same engine, his is keel cooled.
He needs a couple of thousand dollars of coolant to fill it we need about $150 worth

Of course you then need a dry exhaust. I'm on my second automotive (small truck) muffler in 35 years. I'm not sure what it cost me but I don't think it was more than fifty bucks - fifteen years ago.

And his boat NEEDS Air conditioning whereas we do not.
Lot of heat generated by that exhaust.

[skipperpete]

Originally Posted by lituya1617

The lack of critical replies to my dissing of heat exchanger/salt water exhaust injectors would seem to reveal that my opinion carried the day. Or, people could just ignore me...

I agree with you about keel/hopper cooling and dry exhausts but the reality is that it’s very difficult to install, manage and justify this system on most sailing pleasure craft. The extra drag created by an external cooling array on a fiberglass hull negates its usefulness but could be done on a metal hull with no major difficulty, however there still remains the problem of the dry exhaust running through the accommodation, often from mid ships to transom and introducing the problem of insulation to reduce fire risk. Then there’s the noise level and smoke issue, it should come as no surprise that wet exhausts act as scrubbers and often show no visible smoke but dry exhausts lack this advantage and the soot particles are released into the atmosphere and come back aboard to settle on white sails and clean decks. There was an old racing yacht that chartered in the whitsunday group with a dry exhaust that came out the top of the mizzenmast mast so it definitely can be done but the logical technique on the majority of vessels owned by contributors to this forum is to just stay with the wet exhaust and manage it well.

[jimbunyard]

Keel-cooling remains a niche market, despite having been around for almost a hundred years. Like other systems, the advantages (and disadvantages) have to be weighed by application, and it seems that market forces limit K/C to their niche market, despite the supposed 'advantages' listed above.

What's being left out is most telling; added complexity, dynamic challenges, hardware costs, installation complexities, etc., all which work to limit the technology's widespread acceptance.

A good application for the system is for boats working in highly contaminated water like shallow water tugs, inshore fishing boats and dredges.

[botanybay]

Originally Posted by skenn_ie

$2 seal ? Doesn't it have a ceramic/graphite pressure seal ? The gear-driven ones that I have seen have a pressure seal, then an air gap to bleed any water leakage, then an oil seal to keep the oil in the engine. There is no possibility of water getting into the oil.

The water can and does get into the oil. The oil seal is designed to keep oil IN the engine, any pressure from the outside of the seal will go right in.

So, if the water seal is leaking and the weap hole in the air gap gets plugged (corrosion or salt crystals) the output pressure of the water pump will be applied to the OUTSIDE of the oil seal. In this case lots of salt water will get into the engine lube oil.

However, at least on my perkins M90 gear driven Jabsco pump, when an oil analysis showed slightly elevated salt levels in the engine lube oil I checked the pump and found it moist with salt water. Perhaps a drop every 15 minutes... Rebuilt the pump and next oil change had no salt in the oil. (Gotta love those guys at Blackstone labs, their written reports are as valuable as the values themselves). I suspect that once the pump shaft is wet with salt water it can wick past the oil seal. Being that this appears to be the normal failure mode I could see pumps with a small weap hole getting plugged. On the M90 about 1/3 of the area under the shaft between the water seal and the oil seal is open to air so very unlikely to get plugged up :-)

My M90 was made in 1990 and has about 1400 hours on it. I find in southern CA there is so little silt or getting cold that the impeller lasts about as long as a pump rebuild (about 3 years) or about 200 hours of run time. Hoping it will last longer in continuous cruising... perhaps a season? That is the original pump so could be wear somewhere making the seals fail but I suspect salt crystals and sitting being the driver. I also tear down the heat exchangers, water injection flange, etc about every 5-6 years (as soon as I see any corrosion on the heat exchanger) as it is an aluminum housing with a galvanically isolated cupernickle tube stack. The housing is some 3K to 4K to replace!!! Dont want that to get out of hand.