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Can I flood my engine trying to start it?

Nov 26, 2012
1,069
Hunter 34 Berkeley
I read something recently that stated that if you cold crank your inboard diesel for too long you can flood the engine with seawater. As the story went: in the absence of back pressure from the engine the raw water that is pumped into the mixing elbow will backflow into the engine. Is this true? If so it seems like a serious design flaw.
 
May 20, 2016
2,793
Catalina 36 MK1 Everett, WA
yes - typically > 45 seconds before the muffler fills up. I've only once had to turn off the raw water inlet after changing fuel filters to prevent it -- but all boats are different yours may take longer or fill up earlier.

But this assumes you have a wet exhaust with a lift muffler. Its the velocity of the air/exhaust that lifts the water out of the muffler. Most mufflers also have a drain, my manual says if you crank for more than 45 seconds you have to drain the muffler - that's way too much work (the valve is corroded) so I just turn off the input and quickly turn it back on when the engine starts.

Les
 
Oct 22, 2014
9,929
CAL 35 Cruiser Portland OR, moored EVERETT WA
Mark true bit only if you are located near a bay bridge and it is summer. Oh and you have a water muffler in the exhaust line.
It is never a good idea to crank your engine for a long time. If your diesel does not start right away, then there is an engine issue that needs to be addressed.
Some folks use the start motor to crank their engine to get the fuel pump to bleed the fuel lines. This is so they do not have to use the manual fuel pump to bleed the fuel lines. While this is a reasonable idea, it can have consequences... like water in the engine. Options: Install an electric fuel pump, use the manual lift pump, or close the water intake valve and turn over the engine. Just remember to open the water valve once the engine starts. Oh and of the punishments besides water flooding for continuing to crank your engine... burned up starter or dead battery.

Thus the advise often shared... Diesel's are simple. They need Air, Fuel, and compression. If one of these is missing or not being supplied, correct the problem and then try to start the engine.
 
Sep 25, 2008
5,423
Alden 50 Sarasota, Florida
It isn't just when "cold cranking" nor is it a design flaw but rather, as others already said, a normal consequence of prolonged cranking of an engine which pumps water for cooling.
 
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TomY

Alden Forum Moderator
Jun 22, 2004
1,817
Alden 38' Challenger yawl Rockport Harbor
I read something recently that stated that if you cold crank your inboard diesel for too long you can flood the engine with seawater. As the story went: in the absence of back pressure from the engine the raw water that is pumped into the mixing elbow will backflow into the engine. Is this true? If so it seems like a serious design flaw.
It is true! You will flood your engine and I agree, it's not the best design. I had to install a complete water-lift muffler and exhaust on my boat. But there is no avoiding the situation with most wet exhaust installations on sailboats. The engine is usually at or even below the waterline so that gravity cannot drain the system.

On the good side, most raw water pumps draw very little water during the slow rpm's when the starter is engaged. But they do! And the output will vary so you should test to find out.

So it's a matter of volume: How much water can your water lift muffler and hoses hold, beneath the exhaust riser and/ or point of entry once the system is full.

I promised myself I would check to see how much raw water is pulled into the water lift muffler, during engine cranking. Sorry, I haven't done it yet because my engine is a quick start.

It would be a simple matter of draining the water lift, replace plug, crank for say 20 seconds. Empty water
lift into a container. If you do it, let us know the result. :)
 
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Aug 1, 2011
3,457
Catalina 270 Wabamun - on the orange ball
Given the size of the impeller in the pump, you'd think that it wouldn't move a lot of water. On that front, you'd be wrong. :)
 
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Feb 26, 2004
20,692
Catalina 34 224 Maple Bay, BC, Canada
I read something recently that stated that if you cold crank your inboard diesel for too long you can flood the engine with seawater. As the story went: in the absence of back pressure from the engine the raw water that is pumped into the mixing elbow will backflow into the engine. Is this true? If so it seems like a serious design flaw.
"As the story went..." leaves a bit to be desired. "...a serious design flaw" only if it is, and it is not.
What perhaps you missed in what you read (if it was there at all) is the WHY of How It Works, the "It" being the entire exhaust and cooling system.
Before calling it "a serious design flaw," you might want to consider doing some more research as to why they are built that way, so as to understand how it works.
There is a recurrent meme these days: "A feature, not a bug."
In this case, it is neither. It is inherent in the way wet exhaust systems work.
THAT's what you have to learn about.

PS - I'm an engineer, so I know about design flaws. This is NOT a design flaw.
 
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Nov 26, 2012
1,069
Hunter 34 Berkeley
Wow! Thank you for gracing my post with your knowledge and wisdom, Stu The Engineer. In addition to all of your knowledge about diesel engines I think you really nailed the tone I was looking for in a response. Thanks, again.
 
Jan 11, 2014
4,057
Sabre 362 113 Fair Haven, NY
One option when using the starter motor to bleed the engine is to close the seacock and release the compression lever on the diesel. The avoids a hasty trip to the engine compartment to open the the seacock.

Also note, running the water pump dry is not healthy for the impeller. Changing an impeller is much easier and cheaper than dealing with a hydrolocked diesel with a bent piston rod.
 
May 17, 2004
1,869
Beneteau Oceanis 37 LE Havre de Grace
So, naturally I am trying to work out in my head if there is a design to prevent this.
Probably. I'm imagining some complex system of bypass hoses and valves. The thing is, by the time you add that complexity you've added a ton of new failure points, each one of which could cause problems at much worse and unpredictable times than the original design.
 
Jan 11, 2014
4,057
Sabre 362 113 Fair Haven, NY
So, naturally I am trying to work out in my head if there is a design to prevent this.
There is, it is called a dry stack. The exhaust exits the boat directly without going through a water lift muffler. Of course having a 3" diameter SS pipe that is ~800* F running through the boat creates another set of issues.
 
Oct 22, 2014
9,929
CAL 35 Cruiser Portland OR, moored EVERETT WA
DO not think so, but necessity is the mother of invention.
 
Feb 14, 2014
3,859
Hunter 430 Saba Waveland, MS
On the best of water quenched muffler designs, use your ears and eyes to detect a problem.;)
1) Locate your overboard exhaust port.
2) Have someone watch it when cold starting or you listen for the "burping water"
3) Crank your engine.

No water seen or heard "burping" out the overboard exhaust...
STOP cranking and find the cause!

Even do this if you engine starts!!!:)

To find the time between "burps", set engine in idle and count the burps per minute.

This is the "pulse rate" of the heart of your engine.

Boat Doctor...
Jim...
 
Nov 6, 2006
8,419
Hunter 34 Mandeville Louisiana
My 34 will hydrolock after about two minutes of cranking without starting.. early on I got empirical data on that, cranking with compression released while bleeding.. I noticed water dripping out of air cleaner... took me a while to figure what was going on.. removed exhaust hose , closed seacock, then bled engine.. which also cleared the water.. then cranked and she fired right up. put exhaust hose back on, opened seacock and fired back up .. perfect..
EDIT: another way to prevent this is to remove the water hose at the exhaust elbow.. let it run into the bilge while you are bleeding etc.. then hook it back up when the engine starts.. Exhaust pressure is necessary to blow the water out of the muffler and tall hose loop under the stern..
 

TomY

Alden Forum Moderator
Jun 22, 2004
1,817
Alden 38' Challenger yawl Rockport Harbor
So, naturally I am trying to work out in my head if there is a design to prevent this.
With a water lift muffler and wet exhaust, I think the only way is to raise the level of your water injection point to be above your exhaust outlet, likely in the stern.

The idea being that any raw water pumped into the exhaust, can gravity drain out the exhaust port in the stern, before it reaches, and goes over the top of the injection elbow, and into your engine(via exhaust valves).

With most sailboat designs, as the exhaust outlet(and usually a high loop in the exhaust hose above that) needs to be safely above the waterline to prevent back flooding (equally catastrophic!), that would place the raw water injection point above decks.
 
May 20, 2016
2,793
Catalina 36 MK1 Everett, WA
With a water lift muffler and wet exhaust, I think the only way is to raise the level of your water injection point to be above your exhaust outlet, likely in the stern.
.
Nope you’d have to raise it above the high point of the exhaust, which on my water lift exhaust is several inches above cockpit seat level, if you do that no need for a water lift muffler, just let water flow down hill.
 
Feb 14, 2014
3,859
Hunter 430 Saba Waveland, MS
Nope you’d have to raise it above the high point of the exhaust
Nope.
It has to be higher than your high point vent on the sea water pump.
That is there to prevent back flow on engine shut down.

Most water quench exhausts are design for boat engine "dynamics" in calm seas.
When I checked my exhaust system elevations out, I found that my boat would "slosh back" the water seal into my not running engine, in a near bow on sea state of 2-4 feet.:yikes:

Gentlemen start your engines in high seas....
Jim...
 
Nov 26, 2012
1,069
Hunter 34 Berkeley
Kloudie. I assume you would have water in the crank case with hydro lock. Surely, you cannot run the engine that way.