Muff Not The Answer.

[Mr Hemi]

I changed out my Thermostat and hoses.
Ran it on muff and it overheated.???

Was worried I had done something wrong with my installs.
So I took the props off my boat and submerged my Bravo 3 drive into a huge container of water.( 20x12x 28inch container.)

It was about 3 inches higher than my intake vents on my drive.
I filled the container with water, turned the tap on full and put it in the container and let it spill over.(I had my wife watch the container and make sure it was okay.)
As I was running my motor my wife yells at me the water was going below my intake vents.
I shut down the motor.
i waited a couple minutes for the bucket to again fill up with water and we ran the motor again.
Same outcome.

So how do mufflers work if this is what happens?????
They Dont.

Next time your doing maintance,is with muffs on, and your boat overheats, just remember its probably the muffs, not something you thought you messed up.
Like 99% probably.

I finally got my boat up to operating temperature so I could test out my Thermostate and my temp was perfect at 175.
It took about 20 minutes of starting and stopping to allow the container to fill with water, so I could run the motor.
If I had just run it on the muffs, I am sure I would be pulling in more air than water, as the test continued.
Not a very accurate way to check for issues.

[mmwjr]

Muffs do work as the hose pressure is applied directly at the water pick up of the drive. The container you used is way to shallow for running the engine. In a tube this size or much deeper the hose doesn’t apply any pressure as it’s open to atmosphere pressure under this condition and you are relying on the container to stay full. Remember running on a hose is only meant to be done at idle rpm as the hose cannot supply enough water.

[Mr Hemi]

Originally Posted by mmwjr

Muffs do work as the hose pressure is applied directly at the water pick up of the drive. The container you used is way to shallow for running the engine. In a tube this size or much deeper the hose doesn’t apply any pressure as it’s open to atmosphere pressure under this condition and you are relying on the container to stay full. Remember running on a hose is only meant to be done at idle rpm as the hose cannot supply enough water.

For Me:
The Muff did not work.
I ran on Muffs and thats when it overheated.
I ran the test at 1000 RPM.
Thats why I wanted to run a different test.
I hear what you are saying the positive suction and the hose pressure should be enough pressure to not allow air into the system, but in my case it did.

I have been chasing a elevated temperature 185 degrees for 3 years now.
Problem was the guy i payed $500:00 to change out my impellor did not change it out.
Cheers.

[mmwjr]

Glad to hear your issue is fixed.

[shrew]

I'd be interested in seeing the muffs and comparing brands. I used muffs on a Bravo III for many years and never had an issue. I'm not saying you didn't have issues, I'm simply curious if we're looking at all of the variables.

I'm also curious if this is a water pressure issue at your spigot. When I've done this, I was in a place where the water pressure was very high and pushed more water than the intake could take in. A large amount of water would blow out the muff 'cups'.

Here is what I used for years:

[Mr Hemi]

Originally Posted by shrew

I'd be interested in seeing the muffs and comparing brands. I used muffs on a Bravo III for many years and never had an issue. I'm not saying you didn't have issues, I'm simply curious if we're looking at all of the variables.

I'm also curious if this is a water pressure issue at your spigot. When I've done this, I was in a place where the water pressure was very high and pushed more water than the intake could take in. A large amount of water would blow out the muff 'cups'.

Here is what I used for years:

I used these also and did not have a problem.
I could not find them, so i used the cheap round muffs that dont completely cover the intake ports and that was the problem.
Im guessing.