interesting advice?

C

Cobalt 25

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I read this advice recently from a boating publication:

"A pressurized water supply should never be used to feed the raw-water pump of an engine equipped with a water-cooled exhaust system. Applying even a low-pressure supply of water to the raw water pump creates the risk that the water will flow through the pump when it's not operating, or deliver an excessive flow of water if the engine is operating slowly. Either condition can fill the exhaust system with water, which can back up into the exhaust manifold and enter a cylinder." He then advised drawing water from a container instead.

Is he saying I shouldn't use a garden hose and muffs on my fresh water cooled Merc 8.1? Being that it's a trailer boat with over 800 hours and I've successfully used muffs maybe a hundred times, am I missing something here?

Peter
 
If a boat is in the water and you feed water faster than it will gravity flow out the underwater exhaust system or have a waterlift muffler it could happen.
 
"am I missing something here? "

Possibly. The muffs are not "directly connected" and excessive pressure will result in the muffs loosening, and releasing excessive flow. The question is: In spite of this, will the muffs allow too much pressure? and the answer is: in your case, apparently not.

I would not Directly hook in a hose. ie: using a screw fitting on the hose to directly attach, without leakage, into the system. THAT would almost certainly cause issues, as balancing delivery rate and pressure would be extremely difficult. The use of muffs allows excess rate/pres to escape, hopefully at a sufficiently low pres so as to not cause damage.

IMHO. YMMV. This opinion is free of charge, and worth every cent you paid for it...
 
Thousands and thousands of boaters have been using Muffs on their outboards and Inboard/Outboards for decades. Can anybody document a problem that this has caused? Other than a muff slipping off and the unit not getting any water.

G
 
quote:
Originally posted by gcolton

Thousands and thousands of boaters have been using Muffs on their outboards and Inboard/Outboards for decades. Can anybody document a problem that this has caused? Other than a muff slipping off and the unit not getting any water.

G

Click to expand...


G, when you put it that way the law of averages says someone somewhere encountered a freak accident doing it. I am however a betting man and the odds are far in your favor that its okay to use muffs.
 
I generally leave the water pressure low when I am ready to start the engine. As soon as it starts I then increase pressure until it starts discharging excessive amounts of water out of the muffs. It has worked well for me since the early seventies, but I'm always open to learning more about things I THINK I know about.

This same publication also contended that they had never seen stainless steel rust. That caught my attention, and I've always been a little skeptical with their advice ever since.

Peter
 
Muffs are fine, they were talking about connecting the house directly to the hose on the inlet side of the pump. Only a problem if the pressure is left on while not running. BY design the muffs can not hold pressure. On an inboard boat it is another story. I just kink the hose when I shut down.
 
My mechanic always had me start the engine before turning on the water.
There is no pressure forcing water in when the boat is sitting in the water, it is fed by suction.
So to force water in can be bad.
Some hose bibs can throw out tremendous PSI.
Always start engine first, then turn water on.
Those 5 seconds it runs dry will do less damage than forcing water in unless you have a helper or a remote hose valve.
 
I flush my raw-water cooled engine after each use. I believe this advice is geared towards outboards - inboards (at least mine) won't have this problem because...

First, unless the pressure regulator from your water source is bad, you will not get excessive pressure. If that pressure regulator was bad, hoses would burst and the marina toilet valves would probably fail and leak all the time.

Second, unless your impeller is almost gone, there is no way for water to get past the vanes when it is off. If your impeller is bad, you're going to see a trickle of water come out your exhaust when the engine is off. Replace your impeller.

Third, at least for my engine, even with the hose on full blast, it does not cool the engine enough to run it past idle. That tells me that the hose delivers less water than the raw water pump's capacity. Hence there is no way to flood my engine.

Again, this is for my Merc 350. Outboards certainly have a different water cooling system, so you should study your manual or simply call the engine manufacturer for support to see if the above advice applies.
 
quote:


" Applying even a low-pressure supply of water to the raw water pump creates the risk that the water will flow through the pump when it's not operating, or deliver an excessive flow of water if the engine is operating slowly."

Click to expand...

I think that statement is a no brainer. Using a hose under pressure could cause water to get by the pump but the chance of that is slim. Almost everyone only uses the muff when they run the engine. I normally turn on the water and then hop on the boat and start it up; takes 20-30 seconds to hop back on the boat. I don't like running the impeller that long without water.
 
If this is such a big risk why does Volvo put a very nice garden hose connection on the side of all their new I/O engines? Their manual says to turn on the water first, then start the engine. They also recommend that the water pressure be AT LEAST 17 PSI.

Any water that is forced past the raw water pump should simply pass through the manifolds, into the risers and out the exhaust. If your engine is installed correctly with a constant downward sloping exhaust system there should be no chance of water backing up into your engine (whether the engine is runnig or not).

However, boats with water-lift exhaust systems are probably at risk since there is no exhaust flow to purge the muffler. In this case I think you should always ensure the enginer is running for the entire time the water is turned on.

Mike
 
we use this often most speed boats have a wash down system its a hose fitting and check valve on the sea strainer we have a valve on the line feeding the sea strainer we can close and then force water thru the engine all our hoses are aircraft fittings or hydraulic because of the extreme pressure on the inlet side can exceed 400 pounds! we use globe impellers because they are soft and pump well at slow speeds then are soft enough to let water blow by so they act as a restriction we use large pressure reliefs to dump excess pressure out the side of the hull this system we use a lot to cool the headers after running with the engine off i run the water till they are cool to prevent burns the only time this might not work is with water lift mufflers or sail boats if you crank to long with the decompressor on they will fill the exaust, water lift mufflers have drain plugs if you do accidently fill them. you can not force water thru an outdrive with ear muffs unless you sea clamp them in place!
 
quote:
Originally posted by CurrentSea

My mechanic always had me start the engine before turning on the water.
There is no pressure forcing water in when the boat is sitting in the water, it is fed by suction.
So to force water in can be bad.
Some hose bibs can throw out tremendous PSI.
Always start engine first, then turn water on.
Those 5 seconds it runs dry will do less damage than forcing water in unless you have a helper or a remote hose valve.

Click to expand...


You can ruin an impeller very quickly if that water does not get to it soonest.

G
 
quote:
Originally posted by Cobalt 25

I read this advice recently from a boating publication:

"A pressurized water supply should never be used to feed the raw-water pump of an engine equipped with a water-cooled exhaust system. Applying even a low-pressure supply of water to the raw water pump creates the risk that the water will flow through the pump when it's not operating, or deliver an excessive flow of water if the engine is operating slowly. Either condition can fill the exhaust system with water, which can back up into the exhaust manifold and enter a cylinder." He then advised drawing water from a container instead.

Is he saying I shouldn't use a garden hose and muffs on my fresh water cooled Merc 8.1? Being that it's a trailer boat with over 800 hours and I've successfully used muffs maybe a hundred times, am I missing something here?

Peter

Click to expand...


I fail to see where they are giving reference to 'muffs'. What I am familar with is the act of Hydroing. This is common for diesels where in trying to start the engine by cranking for extended periods you can suck water up the exhaust and into the cylinders, causing financial harm.

Absolute,

Suckin Sludge & Havin a Gas
 
The publication was Boat US Magazine.

In the question and answer segment someone asked whether they should hook up a 18 HP diesel to a garden hose so that they could run it out of water. The response is above.

The author made a blanket statement relating it to all engines that were raw water cooled.

Bob
 
I am not aware of any manufacturer recommending starting a motor with a outdrive ie I/o without the water first being put to the drive.

The impellers in the drive or motor mounted such as volvo and bravo motors, will melt in as little as 30 seconds and sometimes break apart.

Then the fun really begins finding the pieces.
 
Few things: 1) adjusting the tap on your garden faucet does not adjust pressure, you only adjust flow even if it is only cracked open and you KINK the hose, the hose will go to FULL pressure. in the case of the muffs, you can only maintain the pressure that the spring back can maintain, the small oriface in the connector is generating the pressure drop to be safe for the lower unit.
2) In the Volvo instance, they havce installed a metering oriface to drop the pressure and control the flow based on a normal standard of 55 PSI water pressure. very simular to the older shower heads..
 
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