Necessary to shut off raw water intake? - SailNet Community

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Old 08-08-2008
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Necessary to shut off raw water intake?

I recently had a mechanic do some work on my Volvo MD 2b 25hp diesel raw water intake engine.

He made the statement that I should always turn off the raw water intake valve for a few seconds before turning off the engine.

My question to the group is this...does that mean that it is necessary that when I go sailing and I turn the engine on and off several times during the outing, that I must turn off the valve each and every time?

Does this make sense? Why would this be necessary.

Thank you for any info.

Sincerely,
Rick
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Old 08-08-2008
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i keep my intake open the whole time i'm sailing. i only close it when i get back to the dock and that is after i turn the engine off. reading the service manual for mine, if the valve is open and you are trying to turn on the engine & it doesn't start, you can eventually flood it. he may be trying to avoid that by having you shut the valve, the engine dumps some water, then you turn it off.
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Rick, I'm not sure what his goal is, but that simply sounds impractical WHILE you are sailing, and might need the engine "NOW NOW NOW" during the day.

Never heard anyone else recommend that, but haven't been intimate with V2b engines, either.
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Thanks guys. I have asked others as well. The manual for the boat (a 1970's Westerly Centaur) also suggests running the engine for 15 seconds with the water intake valve closed before shutting down. I guess given common sense and practicality I will do this at the end of a sailing day. Thank you again.

Rick
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Hello,

It's a good idea to close the valve when you leave the boat.
I don't believe it is necessary to close the valve when you are
on the boat and sailing and will use the motor.

FYI, I never close the valve because on my boat it is too
difficult to reach.

Barry
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Old 08-09-2008
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I had to do this on a boat to prevent flooding the engine. Indeed, when not done, engine struggled to start. Painfull procedure. Months later discovered the exhaust system was wrongly designed (hand made, waterlocker not sized to hold the return water). Once fixed, never had to do it again. It's a weird requeriment, but keep you eyes open or ask someone else to review your entire exhaust system.
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Harp :
I've got the Volvo MD17c, and I have never turned off the intake before stopping the motor.
What on earth for?
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If you have a plastic muffler it can melt if run for 2 minutes without raw water flow. I would think 15 seconds should not hurt anything.
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Quote:
Originally Posted by harpguitar View Post
He made the statement that I should always turn off the raw water intake valve for a few seconds before turning off the engine.

...

Does this make sense? Why would this be necessary.
It can. It all depends. It is my understanding (IOW: I am not authoritative on this subject) that, with certain systems, on certain boats, when the engine is shut off raw water can be siphoned from the exhaust and into the engine. This is a Very Bad thing. Closing the raw water intake a few seconds before shutting off the engine breaks the siphon and prevents this. The other thing you can do is install a raw water anti-siphon loop.

Here's a thread from a little earlier this year: raw water anti siphon/vented loop? where they're discussed. I'm sure that if you search Sailnet and Google, you'll find plenty more on the subject.

The other thing to be aware of is being careful of cranking too much with the raw water intake open. The water lift muffler requires the exhaust from a running engine to empty it. If you crank too long w/o the engine starting, the water lift muffler soon fills up, then the water backs up into the engines exhaust manifold, thence, via the exhaust valves, into the cylinders and, eventually, just about everywhere else in the engine. Very bad.

If I have to crank more than 10-15 seconds, the raw water gets shut off.

Jim
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So it sounds like I really need to make sure I shut off the raw water intake if I have starting problems. Given all that has been said i will 1) turn off the intake for 15 sec before shutdown at the end of a sailing day and 2)I will not crank it for more than a few seconds with the intake open...I will close the valve if I am having starting problems. Fortunately this particular engine tends to start right up.

Thank you again,
Rick
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