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Can I use the flush out fitting as muffs?

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Can I use the flush out fitting as muffs?

Old 10-12-2020, 08:07 AM
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Default Can I use the flush out fitting as muffs?

I was working in my driveway on my yammy a few days ago. It's a 2020 and has a flush out fitting that I attach a hose to and flush it after each trip if I used it in brackish or muddy waters.
But when I went to run the outboard to see if the tach was wired correctly I used the muffs on a hose over the water intake ports on the lower leg.

My question is since this model has a flush out fitting can I use this instead of the muffs when running the outboard in my driveway.
Is there enough water pressure going through that fitting for a cooling flow to not burn out the impeller?
Or should I stay with the muffs?
Old 10-12-2020, 08:14 AM
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Originally Posted by expidia View Post
I was working in my driveway on my yammy a few days ago. It's a 2020 and has a flush out fitting that I attach a hose to and flush it after each trip if I used it in brackish or muddy waters.
But when I went to run the outboard to see if the tach was wired correctly I used the muffs on a hose over the water intake ports on the lower leg.

My question is since this model has a flush out fitting can I use this instead of the muffs when running the outboard in my driveway.
Is there enough water pressure going through that fitting for a cooling flow to not burn out the impeller?
Or should I stay with the muffs?
you'll have to look at your manual.

My suzuki manual says not to start the engine on the port. Only run it using muffs. It also says running it on muffs is the preferred method for flushing.
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Old 10-12-2020, 08:21 AM
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Originally Posted by Codycat View Post
you'll have to look at your manual.

My suzuki manual says not to start the engine on the port. Only run it using muffs. It also says running it on muffs is the preferred method for flushing.
This ^^^ My Yamaha manual says to not run it when connected to the flush port. Specifically "do not perform this procedure (flushing cooling water passage) while the engine is running. The water pump may be damaged and severe damage from overheating can result." IMO, no further discussion is needed unless the manual for your specific model says otherwise.
Old 10-12-2020, 08:23 AM
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I would check the manual, but I'd bet that using the flush port will ruin your water pump impeller. The muffs are a better idea.
Old 10-12-2020, 08:33 AM
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My 2020 Yamaha 115 manual says NO!
Old 10-12-2020, 09:03 AM
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No you can’t (per the manual)
Old 10-12-2020, 09:15 AM
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No you cannot run it without the muffs. The hose flush is just that use a hose and leave motor off.
Old 10-12-2020, 09:17 AM
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No.
Old 10-12-2020, 10:13 AM
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Thanks for all those replies. Now that I read the replies I do remember reading in the manual do not run the motor with the flush port connected.
Old 10-12-2020, 10:29 AM
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Always read the manual!
Old 10-12-2020, 10:41 AM
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So here is a bit of inside info on this...yes, all of the manuals tell you not to do it...the company field engineers tell boatbuilders a different story. They will tell them that you can run the engine on the flush out, but there is a caveat...you cannot run the engine at anything more than idle speed. So why is this, and why are they so adamant in the manuals telling you not to do this? Simple really...when you hook up the flush port, you are essentially pushing water from a t in the flow line out the telltale and backwards through the system down to the water pump and out the intake. When you crank the motor up, the impeller is now pushing that water back up and out through its normal flow path. The impeller on any outboard is cooled by having constant waterflow. Revving the engine under these conditions can starve the impeller and the thing is, you might not even know you were damaging it because the engine is getting plenty of water flow from the flush out. It can also be a problem if you run the engine more than a couple of minutes as you can get more than normal heat buildup between the impeller and the wear plate because it is not getting the full amount of water it would normally get.

So the short answer is no, you should not do it. If you are in a bind and need to crank it up for a minute in the off season just to maintain it, you can get away with it as long as you idle only. The thing about muffs is sometimes they are not much better. The cheap ones that push water in from one side often wont cause enough pressure to push water up to the impeller. The impeller is not self priming. Under normal circumstances when you crank the motor, it is completely submerged in water. Once primed, it will work fine even though on plane it is actually above the water surface as it sits above the anti ventilation plate, but that is compensated for by the amount of water pressure being forced through the intakes because of the forward motion of the boat. Find a set of muffs that has a "Y" tube that the hose connects to and pushes water in from both sides. When I use them, I also use a clamp to tighten the seal of the muffs against the lower unit casing. Even better is if you can set up a drum or trough to completely submerge the lower unit, just like when you put it in the water, this is also better for maintenance because it creates back pressure on the exhaust system.
Old 10-12-2020, 02:53 PM
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Been there done that. Smoked two perfectly serviceable impellers. Muff em!
Old 10-12-2020, 02:57 PM
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Originally Posted by gator1 View Post
So here is a bit of inside info on this...yes, all of the manuals tell you not to do it...the company field engineers tell boatbuilders a different story. They will tell them that you can run the engine on the flush out, but there is a caveat...you cannot run the engine at anything more than idle speed. So why is this, and why are they so adamant in the manuals telling you not to do this? Simple really...when you hook up the flush port, you are essentially pushing water from a t in the flow line out the telltale and backwards through the system down to the water pump and out the intake. When you crank the motor up, the impeller is now pushing that water back up and out through its normal flow path. The impeller on any outboard is cooled by having constant waterflow. Revving the engine under these conditions can starve the impeller and the thing is, you might not even know you were damaging it because the engine is getting plenty of water flow from the flush out. It can also be a problem if you run the engine more than a couple of minutes as you can get more than normal heat buildup between the impeller and the wear plate because it is not getting the full amount of water it would normally get.

So the short answer is no, you should not do it. If you are in a bind and need to crank it up for a minute in the off season just to maintain it, you can get away with it as long as you idle only. The thing about muffs is sometimes they are not much better. The cheap ones that push water in from one side often wont cause enough pressure to push water up to the impeller. The impeller is not self priming. Under normal circumstances when you crank the motor, it is completely submerged in water. Once primed, it will work fine even though on plane it is actually above the water surface as it sits above the anti ventilation plate, but that is compensated for by the amount of water pressure being forced through the intakes because of the forward motion of the boat. Find a set of muffs that has a "Y" tube that the hose connects to and pushes water in from both sides. When I use them, I also use a clamp to tighten the seal of the muffs against the lower unit casing. Even better is if you can set up a drum or trough to completely submerge the lower unit, just like when you put it in the water, this is also better for maintenance because it creates back pressure on the exhaust system.
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