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Closet Powerboater
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Discussion Starter #1
The experience of last weekend, where I thought I had sucked water back from my exhaust into my cylinders scared the $hit out of me. I don't fear too many things on my boat anymore, but $$$uddenly ruining my diesel for good is one of them.

So how can one destroy a perfectly good diesel? Lets get a list going. Let's also get a parallel list of how to prevent destruction.:D Of course proper maintenance, inspections, etc is assumed. This list is meant to be of the sudden causes of premature death.


Ways to ruin your diesel:

1. Loosing oil pressure.
--Prevent by installing a gauge and audible alarm.

2. Overheating.
--Prevent by installing a gauge and audible alarm.

3. Filling your exhaust circuit with water while cranking when cold starting.
--Modify starting system and engine to improve cold starting. Crank with raw water closed. Install raw water diverter for use when cranking for long periods.

MedSailor
 

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Senior Member
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4. Don't be vigilant about inspecting belts and replacing them ahead of failure. ESP timing belts. Few diesels are clearance engines, meaning the pistons won't clear an open valve at TDC.. so if the cam stops and the crank doesn't, WHAM - 2200 rpm to zero in a heartbeat or less.

... don't ask how I know.... If you're lucky you'll just need a head rebuild.. but pistons may be damaged too.

In our case the belt was not old, but a nut vibrated off a belt guide fitting and fell into the crank sprocket, tried to go around under the belt and - SNAP - WHAM - STOP - silence.....

We were three days from home and limped back, sailing when we could and hip-towing our 40' 16,000lb boat with our trusty 5 hp Nissan on our inflatable when we couldn't.
 

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the pointy end is the bow
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6,265 Posts
put off dealing with a worn cutlass bearing, which leads to excessive engine vibration, which leads to a ten pound alternator shaking back and forth, which leads to the timing chain cover breaking open where the alternator bolts on.
 

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Senior Member
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put off dealing with a worn cutlass bearing, which leads to excessive engine vibration, which leads to a ten pound alternator shaking back and forth, which leads to the timing chain cover breaking open where the alternator bolts on.
... and you know this how????;);):)
 

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I've had considerable success over the years in keeping things in safe and top condition but releasing the pull stop prematurely caused my 100 hp diesel to do the back stroke with water from the wet exhaust. Shook the boat but only bent 3 of the 4 con rods.After I did complete re and re for 8 grand I'm much more careful and the bruises on my butt have faded somewhat.As an aside I put a solenoid valve on the riser to drain if the anti syphon were to fail (oil press) Works and I think it's a good idea.
 

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I've had considerable success over the years in keeping things in safe and top condition but releasing the pull stop prematurely caused my 100 hp diesel to do the back stroke with water from the wet exhaust. Shook the boat but only bent 3 of the 4 con rods.After I did complete re and re for 8 grand I'm much more careful and the bruises on my butt have faded somewhat.As an aside I put a solenoid valve on the riser to drain if the anti syphon were to fail (oil press) Works and I think it's a good idea.
I didn't follow that exactly.
What did you do?
 

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Courtney the Dancer
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Overheating has got to be one of the most common ways a marine engine bites the dust. Lack of maintenance is probably the main culprit. Impellers, hoses, hose clamps, water pump belts and circulating pumps can all fail and it doesn't take very long to cause damage if at high rpm. Mostly a matter of maintenance to prevent failures and just using the good old eyeball on a regular basis to look things over. The alarms that warn of a lack of raw water seem like a good idea, although I haven't installed one yet.
 

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Crotchety Old Member
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910 Posts
I have a good one. Our diesel was just reinstalled three days ago after a topside rebuild.

You have to calculate exactly how long your water pump belt will last, wait until about a minute before it breaks. Have someone bump the key off (alarms go off), then wait until you smell paint burning. There you have it - a blown head gasket on a new Yanmar with 140 hours on it!

Then $2200 later your new Yanmar 30 is back up and running.
 

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A couple times I forgot to open the raw water engine cooling seacock after starting the engine. While warming up the engine the overheat alarm went off, opened the seacock and engine cooled down fine. It is raw water cooled so high temp alarm is at about 170 degree- should not have damaged engine.

I did not inspect the raw water pump and since then have run many hours on the engine without pump problems. Could the impeller still be damaged? I plant to change it say every 3 years.
 

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Senior Member
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A couple times I forgot to open the raw water engine cooling seacock after starting the engine. While warming up the engine the overheat alarm went off, opened the seacock and engine cooled down fine. It is raw water cooled so high temp alarm is at about 170 degree- should not have damaged engine.

I did not inspect the raw water pump and since then have run many hours on the engine without pump problems. Could the impeller still be damaged? I plant to change it say every 3 years.

There's a good chance your impeller is somewhat damaged.. they don't like to run dry. They will often continue to move adequate amounts of water despite a broken vane if there's no resulting pluggage... Also suddenly flashing cold water into an overheated block is another way to cause cracking.. probably better off the shut down, allow to cool then open the valve and restart.

Frequency of impeller changes probably should be based on hours more than simple elapsed time, but I know many who do it seasonally just because.

If part of an impeller vane is broken off it will find its way into the heat exchanger (if FWC) or 'who knows where' in the water jackets of a RWC engine. In a H/E it's usually easy to find/flush out. If it gets jammed up inside the engine itself it's very hard to know where it ended up and a passage could be 'starved' at some point. Not a nice prospect.

btw.. some people hang their engine key on the RW through hull valve handle.. tends to discourage 'forgetting'...;)
 
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There's a good chance your impeller is somewhat damaged.. they don't like to run dry. They will often continue to move adequate amounts of water despite a broken vane if there's no resulting pluggage... Also suddenly flashing cold water into an overheated block is another way to cause cracking.. probably better off the shut down, allow to cool then open the valve and restart.

Frequency of impeller changes probably should be based on hours more than simple elapsed time, but I know many who do it seasonally just because.

If part of an impeller vane is broken off it will find its way into the heat exchanger (if FWC) or 'who knows where' in the water jackets of a RWC engine. In a H/E it's usually easy to find/flush out. If it gets jammed up inside the engine itself it's very hard to know where it ended up and a passage could be 'starved' at some point. Not a nice prospect.

btw.. some people hang their engine key on the RW through hull valve handle.. tends to discourage 'forgetting'...;)
By leaving the raw water seacock closed will the impeller actually run dry? The way my engine is set up the engine is below the water line. So when the seacock is closed, the water pump is flooded. Now when the pump starts, it cannot get a suction of water, but is the pump still flooded with water? I am not sure how it would go dry as that would mean their would need to be a total vacuum at the pump.

I will plan to replace the impeller just a precaution in any event. That would be bad if pieces start breaking off.
Regards
 

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By leaving the raw water seacock closed will the impeller actually run dry? The way my engine is set up the engine is below the water line. So when the seacock is closed, the water pump is flooded. Now when the pump starts, it cannot get a suction of water, but is the pump still flooded with water? I am not sure how it would go dry as that would mean their would need to be a total vacuum at the pump.
These units are pretty close to being 'positive displacement' pumps so they will push water out.. in any event I'd worry about heat from friction without the steady supply of intake water.

Certainly check your impeller for peace of mind... or change it, for that matter, for the same reason..
 

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Letting a raw-water-cooled Volvo MD 17C freeze in fresh water is one way of nearly wrecking a motor. The aft barrel cracked, and still drips a wee bit, but it survived.
I was lucky.
 

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here's a great other way to buy yourself a new prop shaft key , prop shaft coupler, and gearbox, while w rrecking your summer vacation ...:

run your faithful OEM diesel engine for 30 years, ignoring its ever-increasing noise, as it vibrates its engine mounts down to thin shreds and throws off your prop shaft alignment so that your p shaft is whining, out of alignment and stressing against its retaining key.... then ignore the weird noises until your prop shaft coupling bolts break, your key shreds itself and your prop shaft, now unrestrained, floats out the back of your boat until it hits the rudder, at which time you realize you no longer have (1) any forward momentum (2) any rudder and (3) w ater pouring into your boat thru the stuffing box hole where your p shaft used to be firmly held. then you are forced to interrupt your cruise, because you have no workable engine or p- shaft or p shaft key. then hope to #$%^ that some mechanic in a foreign port you'll never visit again will interrupt his regular workload to (a) mill you a new prop shaft key (b) order you up a new coupler (c) fix your wrecked marine gearbox. and while you are at it, reject the mechanic's kind offer to replace your wornout engine mounts which is about $300 of cost and $150 of labor since every thing else is in pieces. and insist that he REINSTALL the same wornout engine mounts you've used for 30 years. and discount his advice to install a flexible coupling or aquadrive (recommended in case you are ever this stupid and cheap again) and further insult the local folks at the dock who allow as to how it might have been a good idea to at least CHECK the height of the engine mounts, and faceout of the p-shaft coupling, a t least every year ??


moral of the story:
check your prop shaft alignment and engine mount heights at least yearly. if the faceout on your p shaft coupling is increasing-- ie 'out' -- then do something about it or hire someone who knows what to do about it. or
figure out how to measure your own p - shaft face out and adjust your own engine mounts.

we try to help out visitors with mechanical troubles, but guys like this don't need to come back for the next century...
 

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I should have read this forum before sailing but luckily none of that happened to me. I hear everyone and I mean everyone who sails saying change your impeller. I changed mine and the new one sucked.....so I took it apart again and but the old one back in. Works like a charm. Plus, they work fine even with tabs broken so I don't see the huge emphasis here. When the engine overheats....change it. I don't have a temp sensor on my YSM 12 but it shuts off automatically when it gets too hot. This is usually, when I leave the seacock closed or the mixing elbow on the exhaust gets clogged/blocked which seems to happen about every 24 hrs of run time. I hear everyone praising the Yanmar engines but I've never had more trouble with an engine. The one thing I would praise is I've been able to fix everything....pretty easy to work on. Well almost....currently I'm mounting a little 8 hp evinrude to the transom...not sure whats wrong with the Yanmar now. Won't spin. Probably water in the chamber which .... rebuild or replace with something better. It's on a Hunter 30 and only ran 4.5 knots. I'd love to get something that'll get me 6.0 knots.
 

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Those little bits of rubber impeller are probably jammed in the input side of the heat exchanger waiting for the right time to make their presence known. Maybe an engine room flight plan/check list would help with over heating by ODF (oops dang forgot)
 

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I should have read this forum before sailing but luckily none of that happened to me. I hear everyone and I mean everyone who sails saying change your impeller. I changed mine and the new one sucked.....so I took it apart again and but the old one back in. Works like a charm. Plus, they work fine even with tabs broken so I don't see the huge emphasis here. When the engine overheats....change it. I don't have a temp sensor on my YSM 12 but it shuts off automatically when it gets too hot. This is usually, when I leave the seacock closed or the mixing elbow on the exhaust gets clogged/blocked which seems to happen about every 24 hrs of run time. I hear everyone praising the Yanmar engines but I've never had more trouble with an engine. The one thing I would praise is I've been able to fix everything....pretty easy to work on. Well almost....currently I'm mounting a little 8 hp evinrude to the transom...not sure whats wrong with the Yanmar now. Won't spin. Probably water in the chamber which .... rebuild or replace with something better. It's on a Hunter 30 and only ran 4.5 knots. I'd love to get something that'll get me 6.0 knots.
Sounds like you need a temp gauge or over heat alarm- give you some warning before the engine dies. Or install a flow alarm- check
https://www.aqualarm.net/comerus/store/comersus_listCategories.asp
and maybe install new mix elbow.
 

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Crotchety Old Member
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I should have read this forum before sailing but luckily none of that happened to me. I hear everyone and I mean everyone who sails saying change your impeller. I changed mine and the new one sucked.....so I took it apart again and but the old one back in. Works like a charm. Plus, they work fine even with tabs broken so I don't see the huge emphasis here.
Stay subscribed to this thread. Then you can let us all know how much you will spend on your future rebuild. Start saving for it now.
 
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