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Author Topic:   Best Method for Flushing 90HP 4-stroke
drewc posted 05-09-2003 09:18 PM ET (US)   Profile for drewc   Send Email to drewc  
Hi! What is the board's opinion re *best* way to flush my new 90 HP Merc 4-stroke on my new 170? Dealer was confusing...said I may do *either* the "connect the hose to the flush port and run the engine at idle only" OR attach the *earmuffs* and connect the hose/run engine to flush" method. Challenge is that boat is at dock and no way to attach earmuffs w/out raising engine out of the water, and several mechanics said running that way was a *nono* due to improper oil circulation. So, what's the best way to do this important end-of-day task? Thanks in advance...
Dick posted 05-09-2003 09:54 PM ET (US)     Profile for Dick  Send Email to Dick     
drewc

Need a little more info.
I am guesing that you are in salt water. If so use the flushing port with the engine down, it will flush the engine fine at idle.
Most people never flush when moored.

Dick

boxers posted 05-09-2003 11:40 PM ET (US)     Profile for boxers  Send Email to boxers     
Many of the 4 stroke Yamahas (115, 200 and 225) have attachments for a hose to connect. Not sure if Mercury carried this over?
boxers posted 05-09-2003 11:42 PM ET (US)     Profile for boxers  Send Email to boxers     
Our mechanic said the motor doesn't need to be running on the Yamaha F225. I hope this is correct?
jaccoserv posted 05-10-2003 04:14 PM ET (US)     Profile for jaccoserv  Send Email to jaccoserv     
I believe that your motor has the hose attachment, if so, no need for earmuffs. Just run the water through the hose with the engine down, no need to run the engine during this procedure, if you desire so however, do not run past idle.
dgp posted 05-10-2003 05:40 PM ET (US)     Profile for dgp  Send Email to dgp     
Drewc,
First read your Owner's Manual. My Mercury 4 stroke manual has a detailed description on how to flush the motor.
The engine has to run, at idle, for at least 5 minutes so that the thermostat will open and you get fresh water flushing everywhere in the cooing passages.
fno posted 05-12-2003 08:45 AM ET (US)     Profile for fno  Send Email to fno     
Drew, I have a 90 4 stroke also. The most effective flush is with muffs as described. The flush port on the back is for use when the motor is off. I usually do both if I have time, muffs first then the port. The port is most valuable for boats kept in the water as they permit flushing of the power head at least, the lower unit will still get salty
Tallydon posted 05-12-2003 08:23 PM ET (US)     Profile for Tallydon  Send Email to Tallydon     
Drew,

The problem with attaching to built in flush mount can be water pressure, or too much water pressure. My dealer told me to avoid it and use the muffs. He has seen numerous blow outs because of too much water pressure. By the way, I have a Yam F100 4 pounder.

FISHNFF posted 05-13-2003 01:49 AM ET (US)     Profile for FISHNFF  Send Email to FISHNFF     
drewc,
I have had ny Merc 90 4S for 2 1/2 years, and it spends its Summers moored in salt water on my 17 Alert/Montauk. I use the flushing port while the motor is tilted clear of the water. If it were down, it would suck up saltwater too. I attached a hose quick connect to my water port/"pee" hole, so I use it when when the boat is on the trailer. I believe the motor must be run to allow the thermostat to open, ensuring proper flushing. I asked my dealer about flushing while tilted, and he said OK, just at idle.
The only problem I've had flushing (knock on wood), is that the rubber female fitting on the motor will pop loose from its seat and fall in the motor. Sounds wierd until you see it. Then you must pull it out and reseat it.
Otherwise A O K.
Hope this helps,
FISHNFF
tabasco posted 05-13-2003 03:48 PM ET (US)     Profile for tabasco  Send Email to tabasco     
That rubber is a real pain in the $SS. It keeps getting pushed into the motor and its not so easy to reseat it. I finally stopped using it and bought ear muffs
BMR posted 05-13-2003 06:24 PM ET (US)     Profile for BMR    
I have been flushing a Merc 90 4 stroke per the manual by just using the fitting on the back of the cowl and running the water with out the engine running. 1516 months and every is fine. I am a believer in following the manufacturers instructions.

I think using this fitting will also be safer since you are doing this to a boat in the water.

chaimemet posted 05-13-2003 10:45 PM ET (US)     Profile for chaimemet  Send Email to chaimemet     
that fitting popped inside for me on the first try. Maybe a quick release coupler would fix the problem. Meantime I use the muffs and every other time use Salt away.

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