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Old 18-01-2009, 01:49   #1
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Can you explain...

So how i understand it the exhaust on your engine and raw coolant water mix and the exhaust pushes the water up and out...

Why is this???

and If the engine doesn't start right away and push the water up and out can
it back flow to the engine and hydro-lock the engine and well destroy it???

beetle
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Old 18-01-2009, 03:00   #2
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Our engines use heat exchangers to cool them fed by raw water and yes if you have a hard starting engine..keep you raw water sea cock closed till she fires or you can flood the engine from the raw water pump back through the exhaust valves.

Why?...we dont have adequate air flow to run radiators for a closed system and the side benifit is relatively cool exhaust gases as well as engine room..its a good deal actually but with the typical electrolysis issues we have to deal with as a down side ...nothings perfict.
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Old 18-01-2009, 04:48   #3
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Re: Exhaust System Fundamentals ~ by Dave Gerr

This is a diagram posted by GordMay...I hope I'm not breaking any rules in reposting it.
Keep in mind that there are variations to these.

The top diagram is probably the most common in modern sail boats.

The bottom diagram, in my opinion, is the safest way to go in that the highest point in the system is dry and directly behind the engine.
Over cranking would not flood the engine with this set-up.

Unfortunately this is not always possible with conventional lay-outs and it requires a longer piece of non water cooled exhaust that needs insulated…also vibration of the dry stack needs addressing.
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Old 18-01-2009, 12:16   #4
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will cranking the engine with out having the sea cock open fry the impeller
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Old 18-01-2009, 13:31   #5
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After replacing the fuel filters, I usually have to crank the engine for 30-60 seconds to get it to fire up. I close the raw water intake seacock almost all the way, leaving it cracked in order to allow some water in to lubricate the impeller, but not enough to fill up the exhaust system.
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Old 18-01-2009, 14:59   #6
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Quote:
Originally Posted by beetlejuice30 View Post
will cranking the engine with out having the sea cock open fry the impeller

Yes...Eventually it will. Definitely not good for it.
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Old 18-01-2009, 16:09   #7
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Yes...but in actuality very little due to the fact that it is heat caused by friction that does most of the dammage to impellers and your talking less then 60 rpm..so unless as mentioned your bleeding an engine and laying on the starter for a long time I personally dont even worrie about it...

Exanple:
1 min or less total time in shorter 10 second spurts cranking up a cold blooded engine or low compression engine is not going to vaporize all the water from the pump and harm the impeller, water is the lubricant...

Id rather replace an impeller then bend a rod from hydraulicking a motor wouldt you?

My procedure for a cold start is this if Im alone..I keep it closed..start the engine and dash below to open it...so Im getting a couple seconds at 3 to 4 hundred RPM at the pump..which would translate into 30 to 40 compleat revolutions to the impeller before it got water if it took me 6 to 8 seconds to get below and open it.

If I have crew I have someone open it as soon as it fires from a cold start...of course most new or warm diesels should fire within a revolution or two so there is no issue anyway.

Just my Opinion... and FWIW..I change mine every two years in my boats not yearly because I cant use them that much yet..and I havent pulled a broken one yet.

Hope this helps
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Old 18-01-2009, 16:11   #8
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i Understand that plenty of people are able to eliminate the problem as long as they are aware of it.
but does any one make some kind reed valve for the exhaust before the water enters the system, to prevent water from back flowing in to the engine

does this idea make any sense???
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Old 18-01-2009, 16:17   #9
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Invent one your co. will guarantee a replacement engine if it fails and I'll install one other then that my way is simpler and guaranteed..

Your making to much out of this methinks..
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