Pontoon Boat & Deck Boat Forum

Ok guys, I've touched on this subject in the past, but being new to boating this season, I still need alittle advice... My boat has a Yamaha 75 horse 4 stroke on it. There is a "hose connection" on the upper unit that allows you to "flush" your motor. I have used this proceedure several times and the water has flowed freely from the " pee hole" on the upper unit as well as running out freely on the lower unit. When I have done this, I have not run my motor, just flushed it. I also have read on here about using ear muffs.. so first of all, what's the best way to flush, upper unit hose connection or earmuffs. It would seem that upper unit would be good simply because the water runs all the way thru the motor, top to bottom. Secondly, if using the upper connection or using ear muffs, are you supposed to run your motor also. I ask what seems like a stupid question because everytime i've been around someone using earmuffs they ran the motor, but when I asked the mechanic at my boat dealership about using the "upper unit flushing system", he told me it was not necessary to run the motor. So you can see why an inexperienced boater would be confused. Thanks in advance for your help.

The upper flush port (hose on the cowling) was originally designed for boats that stay in the water...it has since become a fairly standard feature on most outboards and NO you should not run the engine using this method. As for which method works best...both do a good job of flushing. I personally prefer to use the flush muffs on the lower unit and run the engine for 15-20 mins... it's really personal preference as either will work good as long as you flush it regularly after use in salt water.

Why are you flushing so much?? Are you in salt water?

If you use muffs then you have to run the engine (because water is being applied before the impeller). That is my preferred way of flushing an engine because it cleans the impeller section more thoroughly. IMO

Running the engine with just the hose connection is not recommended because not enough water is in the impeller housing and could cause impeller failure.

I an engine running muff guy but that is a personal preference.

The hose connection at the upper unit comes in handy while I'm docked in salt water. After a day cruising the Inter-coastal Waterway of Florida, I hook up the hose and flush fresh water to clean out the salt and sand with the engine raised out of the water. My owners manual says to not run the engine when using the hose connection and to not run high rpm when using the muffs.

I guess each motor is different. I have a Mercury 90HP 4 stroke and manual says to attach hose to the fitting in the upper unit, turn hose on 1/2 way, and you MUST run the engine in idle.

jmiliz wrote:I guess each motor is different. I have a Mercury 90HP 4 stroke and manual says to attach hose to the fitting in the upper unit, turn hose on 1/2 way, and you MUST run the engine in idle.

Done mine this way twice since I had the boat, no problems. The owner's manual on the mercury dose say to do it this way. It dose seem weird to have the engine running with no muffs

Follow you manual and you can't go wrong

Most dealers keep a muff attached to a hose. It is easier for them to just slap the muff on rather than taking out the plug (if your motor has one). Personally, I don't see a problem with using the flush port provided, as long as you have water coming out the pee hole and around the prop, you have full circulation. The only way, I know of this causing a problem, is if there was a backflow preventer or check valve that would stop the circulation of water through the cooling system. If you feel better using the muffs do that.
doc

I have a 90 HP Yamaha and I flush with the hose connection (boat is stored on a lift). It is run in salt water and I flush after every trip for 15 minutes.

Is it necessary to flush after every trip?

Oldboater wrote:I have a 90 HP Yamaha and I flush with the hose connection (boat is stored on a lift). It is run in salt water and I flush after every trip for 15 minutes.

Is it necessary to flush after every trip?

If you're running in salt water I would think you need to flush at the end of every trip. jmo

May seem like overkill, but I do both I flush with the hose adapter for about 5 mins with engine off, and then for about 5 mins with earmuffs and the engine running. I run most of my trips in salt or brackish water, so I flush after every trip. I think you should do it after every trip regardless of weather it is in salt or fresh. Most lakes have some sediment or algae in the water. Your garden hose is a lot cleaner water than murkey lake lake water with suspended sediment in it. It only takes a few minutes, and

A couple pieces of advice about flushing I have learned the hard way.

1. Never walk away or go inside to answer the phone while the engine is running. (I did this one time, only to return 2 mins later to an audible overheat alarm. YIKES! The motor was not getting enough water due to some algae build up on my intake screens on the lower unit).

2. Always check that screen to make sure it is clear of debris (came from screw up number one).

3. Make sure the hose has plenty of pressure and it has made a good seal around the intake screen (no hose kinks, on all the way etc).

Happy boating brother!