thanks and muff question

Joined
Sep 18, 2017
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4
Even though I just joined (so I could start participating and ask questions), I have been referring to this forum for a long time while shopping for a used boat again.
Any time a seller said there is something wrong with his boat for sale, I would type in a google search. This forum was usually at the top and even when it wasn't, it has always been the best resource.

Eventually, I just started referring to this forum to get answers first, without the google search!! Thanks for all of your time and efforts to everyone who participates!

Question: I was reading somewhere a couple of months ago about muff use on some forum, don't remember which one.
Someone said to never use muffs for more than 45 seconds and never exceed idle.

I never knew this and in 35 years of boating, I have never had a problem breaking these "rules". Have I been lucky or is that bad info?

thanks again !!
 

sogood

Petty Officer 1st Class
Joined
May 11, 2016
Messages
361
I imagine it would be very difficult to run tests etc. on an engine if you were restricted to running on muffs for only 45 seconds. Apart from that, you would often/usually need to get the engine up to normal running temperature, which is never going to happen in 45 seconds. How else do you check normal idling operating temperature, choke operation. Admittedly, some tests, by their nature must be run on the water, under load. Otherwise it's muffs. Provided you have a sufficient water supply I can't see any issues.
​I might have occasion to give the throttle a little "dart" but I wouldn't rev it up constantly and I think the usual recommended max would be 1500 rpm's on muffs, but I may stand corrected on that.
 

JASinIL2006

Vice Admiral
Joined
Feb 10, 2012
Messages
5,525
I think the Mercruiser recommendation is 1500 RPM max. If you go much above that, you have problems getting enough water through a normal hose at city water pressure, and you revving the engine above 1500 can collapse your hose as the pump tries to pull water faster than the hose can deliver.

You can run it as long as you like on muffs. Mine will get up to operating temp on muffs, but it takes a while.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Sounds like nonesense.
As mentioned. As long as it's getting cooled, it's fine. I wouldn't be revving it much though.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
70,468
Ayuh,.... So long as yer supplin' more water to the muffs than the motor can use, it'll run Forever,....

Really no reason at all to rev the motor over 1500 rpms on the muffs anyways, except to make noise,....
 

JoLin

Vice Admiral
Joined
Aug 18, 2007
Messages
5,146
Can't tell you how many times I've run on muffs for a half hour. Temp gauge never moves out of the safe zone. The one exception is a 5.7 Volvo Penta I owned. Temp gauge would slowly rise above normal if I ran it too long, but again, I'm talking 20 minutes or more. I could run my Alphas all day on muffs if I wanted to.

My .02
 

H20Rat

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Joined
Mar 8, 2009
Messages
5,199
Can't tell you how many times I've run on muffs for a half hour. Temp gauge never moves out of the safe zone. The one exception is a 5.7 Volvo Penta I owned. Temp gauge would slowly rise above normal if I ran it too long, but again, I'm talking 20 minutes or more. I could run my Alphas all day on muffs if I wanted to.

My .02


On every alpha I've owned, the hose is supplying quite a bit more water than the engine will take. No matter how well the muffs fit, once you have water pressure and the engine is running, there will be water spraying out by the muffs.
 

JoLin

Vice Admiral
Joined
Aug 18, 2007
Messages
5,146
Did it again yesterday when I winterized the engines. 10 minutes to come up to operating temp, then another 15 minutes to give it a good flushing. Zero issues, and like Smokingcrater said, there's always water spraying out the sides of the muffs.

My .02
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
One thing I noticed:
I had to get a new set of those dual inlet muffs and they seem to be making the rubber stiffer and harder than it used to be. When running my Cobra on the hose it did not prime as well as before. I switched to the Merc/Quicksilver ones with the steel rod/clamp that goes through the water intakes and holds both halves tight to the lower unit. These cost more but seal better.

For those with Volvos and Bravos I came up with a little trick to get the impeller to prime faster and reduce wear on the impeller, used it on the Cobra and it works great:
Hook up your muffs and hose but don't turn on the water yet.
Get a funnel, water container and a screwdriver.
Go up the the front of the engine and disconnect the raw water intake hose at the impeller housing (V/P or Bravo) or thermo housing (Alpha or Cobra)
Put a funnel in that hose and fill it with water till you hear it leaking out around the muffs. Then re connect that hose & turn on the water. This will allow the impeller to prime much faster ESP with engine mounted impellers, because water will get to it quicker. It will fill that hose, and the water passage in the drive and the muffs & hose. Impellers can't suck air too well but suck water very well.
 
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