A question about muffs...

[RandyBC]

No not those kind ;-)......

Being new to motorboats and inboard/outboard engines I've run mine a few times with muffs attached to a fairly high output garden hose. I'm now reading in various source not to open the tap all the way and to keep the pressure low. My questions are: #1 Why? #2 Have I likely screwed anything by ignorantly not following this advice initially? #3 What signs/symptoms would there be if I damaged something.

The engine is a merc 5.7 with alpha one outdrive.

 

[86 century]

Re: A question about muffs...

I use a 3/4" hose the pump is set to 60psi.

You will not hurt it with to much pressure what I doesn't want will spray out around the muffs.

Not giving it enough will kill the impeller real quick so give here all you've got she will spit out what she don't want.

 

[tpenfield]

Re: A question about muffs...

I have never read those various sources and my understanding is quite the opposite.

Think about it . . . what happens when you turn on the hose with the muffs on? Water squirts out the sides of the muffs. When you start the engine, less water squirts out the sides . . .

The muffs have this wonderful way of relieving any excess pressure by letting water squirt out its sides.

So, you can keep your boat in peace.

I my own experience, I have found that the hose sometimes does not provide enough water, rather than too much.

 

[TimeZone]

Re: A question about muffs...

I think under certain circumstances it might be possible for the engine to ingest water. I'm not sure how/why this could happen unless the impeller is shot and lets water past when the engine is not running?
I'd be interested to know why this service bulletin was put out as well.

 

[Scott Danforth]

Re: A question about muffs...

never run the engine faster than 1500 rpm on muffs. your garden hose will supply only about 7gpm. your cooling system in the water will use about 20gpm. that being said, open up the faucet full.

other than that, your muffs will relieve pressure like everyone mentioned.

 

[Don S]

Re: A question about muffs...

Actually the owners and service manuals say to not use over half volume of city water. They also say not to run over 1500 rpm as the suction from the pump will collapse the hose.
I have always run with the hose full on with no problems. The worst that can happen is the water pushes the muffs out of place. I always had a small diameter rope I used to hold the muffs in place.
You can't damage anything that I am aware of, and I worked on them for a living.

Here is what it says in manual #10 as an example.
\

 

[RandyBC]

Re: A question about muffs...

Thanks to all! I'll just carry on then.

 

[thumpar]

Re: A question about muffs...

You probably heard that from someone that is into jet skis. Those 2 strokes will eat water if not running and have the hose on.

 

[RandyBC]

Re: A question about muffs...

Nope. As Don pointed out it is written in the service manual and in the basic engine manuals.