Water pressure in muffs with engine off-BAD?

[gozierdt]

In another of todays threads

http://forums.iboats.com/showthread.php?t=436445

it's mentioned that the posters mechanics thought the reason he found water in his engine was because he left the water pressure on his muffs while he re-installed the seats, put on cover, etc. Is this a real concern for running the engine on muffs? When I run my 88' 4.3 LX on muffs I typically am alone, so I turn the water on, walk to the boat, start the engine, do whatever I want to accomplish, turn off the engine, climb out of the boat, walk over 30-40 feet, and turn the water off. I never considered there should be a time limit on turning off the water. Is this a problem? From what I understand of the cooling system this shouldn't be a problem unless I have manifold leaks.

 

[Don S]

Re: Water pressure in muffs with engine off-BAD?

It shouldn't be a problem, and even if it did back up into the engine, it would be in the cylinders not the oil. You would also have a hydrolock because the cylinder was full of water.
Believe it or not, most people that visit "Marine shops" seldom get to talk to a mechanic or anyone really familiar with the workings of a boat. Usually it's a parts person or some other non mechanical person that says things they shouldn't.

 

[NHGuy]

Re: Water pressure in muffs with engine off-BAD?

If you get some quick disconnects with a ball valve shutoff you can rig up a nice easy on off valve for your muffs. I got these at a discount shop up here called Ocean State Job Lot, but I have seen them at Walmart too.
So get 2 garden hoses, a muff, a ball valve, and optionally another quick disconnect so you can switch between the muff and your sprinkler or spray nozzle.
Put a hose onto the house valve, put the ball valve on the other end, then put the 2nd hose next, and finally the muffs. Close the ball valve, open the house valve, install the muffs to your drive. Bring the ball valve into your boat. Run and watch the water for a short time to be sure it is flowing to the pump pickup ports, then start your engine.
I did some work this week including some carb adjustments and a compression test. I ran the water every time I turned the engine over. Had it out the following 2 days no issue. I ruined my first impeller before I ever dunked my boat. In the yard playing "vroom". Never again.
It might be over kill, but I think of it as precaution.

 

[a70eliminator]

Re: Water pressure in muffs with engine off-BAD?

Or you can just jump out and kink the hose, that's what I do and for no other reason than flooding out my driveway and wasting water.

 

[dozerII]

Re: Water pressure in muffs with engine off-BAD?

Any garden center will have a small ball valve that will thread onto the male end of the garden hose then into the female end of your muffs, so you can shut the water off right at the out/drive. That's what I do and the valve cost $3.99.
Glen

 

[bigdan1]

Re: Water pressure in muffs with engine off-BAD?

I must say ,I read good ones here !

seriously ,unless you have special high pressure system
I dont see how tap water pressure could do this .....
the impeller pusshes the water up in the system .....

by what i read now , the impeller would be useless on tap water pressure !

non sense ...another urban legend!

 

[NHGuy]

Re: Water pressure in muffs with engine off-BAD?

Any garden center will have a small ball valve that will thread onto the male end of the garden hose then into the female end of your muffs, so you can shut the water off right at the out/drive. That's what I do and the valve cost $3.99.
Glen

Yeah but my point is that you can turn it on & off inside the boat without hopping in and out. This saves water and reduces messes.

The original question was about muff water over filling the cooling system. It can't.

 

[EddiePetty]

Re: Water pressure in muffs with engine off-BAD?

"The original question was about muff water over filling the cooling system. It can't."

...and I can agree with that statement,but:
...if the OP has a defective impeller (missing blades/collasped blades) muff water can fill and pressurize the cooling system with the engine shut off.
Just another vote for closed cooling systems!!!!

 

[NHGuy]

Re: Water pressure in muffs with engine off-BAD?

I don't understand where any effective pressure could occur. But we are probably speaking of the same thing. As far as I see any water that gets by the impeller just flows through the system. And I agree a bad impeller can be masked by muff water pressure & flow.

 

[bruceb58]

Re: Water pressure in muffs with engine off-BAD?

...if the OP has a defective impeller (missing blades/collasped blades) muff water can fill and pressurize the cooling system with the engine shut off.

Impossible since the water exits out the exhaust.

 

[a70eliminator]

Re: Water pressure in muffs with engine off-BAD?

Impossible since the water exits out the exhaust.

Right after excessive pressure lifts the thermostat off it's seat.

 

[bruceb58]

Re: Water pressure in muffs with engine off-BAD?

Right after excessive pressure lifts the thermostat off it's seat.

That may possibly happen depending on how bad the impeller is. There are passages to the exhaust manifold that bypass the thermostat though.

 

[bigskiohio]

Re: Water pressure in muffs with engine off-BAD?

from experience ,bad but experience ,do not run full city pressure on muffs or you will blow out seals in pump. Also mercruiser says that motor should be running as the pressure keeps water out , i ran water thru mine with engine off and next thing i hear is a big clunk when starting . i pull plugs change oil . no damage but a pain so now i make it a two person job as soon as water hits outdrive i start and i turn water off same time as motor. yes i probbaly have a leaky gasket in riser but mercruiser bulletin says no bigee. so bad well not on a new boat, on older i would say yes.

 

[Dshow]

Re: Water pressure in muffs with engine off-BAD?

My 2 cents... Better safe than sorry. Don't leave the pressure on the muffs any longer than you need to.